Professor William Gelletly

The conversion electron spectra of the 29.9 and 31.6 keV transitions in 223 Ra which are excited by the α decay of 227 Th have been studied using the Chalk River [Formula: see text] spectrometer. The shapes of the L and M subshell conversion lines of the 29.9 keV transition differ significantly from those of the corresponding lines of the 31.6 keV transition. This observation confirms the difference in line shapes first reported by Valadares, Walen, and Briancon. The conversion electron spectra which are coincident with α particles which penetrated normally through the source backing have also been measured. The coincidence arrangement selects the component of the conversion electron spectrum contributed by atoms recoiling freely into the spectrometer vacuum. The conversion lines of the 31.6 keV transition appear as single doppler-shifted components which are displaced toward higher momentum relative to the main peaks of the singles spectrum. The conversion lines of the 29.9 keV transition have a more complex structure. The doppler-shifted peak is less pronounced for these lines and 68 ± 10% of the intensity in these coincidence spectra appear in broad momentum distributions lying some hundreds of electron volts lower in energy than the doppler-shifted peak. These observations provide support for the explanation which Valadares, Walen, and Briancon have advanced to account for the anomalous appearance of the conversion lines of the 29.9 keV transition in their singles spectra. From the coincidence spectra measured in this work together with results from the charge state studies of Perrin and de Wieclawick, we infer that the L II , L III , and M III binding energies in 223 Ra atoms of mean charge + 12 are 239 ± 32, 216 ± 25, and 212 ± 38 eV higher than the corresponding binding energies in 223 Ra atoms of mean charge + 1.

Levels in the neutron deficient 142Gd and 142,144Dy nuclei have been identified using multiple particle-gamma coincidence techniques. The isotopes were produced in the 54,56Fe + 92Mo and 52Cr + 96Ru reactions at 20–30 MeV above the Coulomb barrier. The new data are discussed in the context of the systematic trend toward deformation in light rare-earth nuclei and the disappearance of the Z = 64 subshell gap.

The γ spectra of the neutron-deficient nuclei 49Mn and 49Cr have been observed using the reactions 12C( 40Ca, p2n) 49 Mn and 12C( 40Ca,2pn) 49Cr at E(Ca)=160 MeV.Radiation from 49Mn and 49Cr was identified by detecting recoil ions in a 0° mass separator. Data from γ-γ, recoil-γ and recoil-γ-γ coincidence spectra and recoil-γ angular correlations allowed the level scheme of 49 25Mn 24 to be deduced up to 6 MeV (19/2 −).The levels of the mirror nucleus 49 24Cr 25 were observed to over 10 MeV (27/2 −). Relative Coulomb energies for the mirror states were found to have a smooth J dependence. The rotation-like level spacing at low spin is interrupted at J=19/2 −, and this is interpreted as an alignment effect.

An extensive study of the level structure of 189Os has been carried out using the (n, γ) and (n, e −) reactions. The use of the average resonance capture technique ensures that the complete set of 1 2 − , 3 2 − states has been established up to 1500 keV in excitation energy and secondary γ-rays have been measured in singles and coincidence to build up the detailed level scheme. The results are compared with existing Nilsson model calculations and with the results of algebraic models. None of the approaches are able to provide a satisfactory description of the negative-parity states.

In an experiment with the BigRIPS separator at the RIKEN Nishina Center, the fragmentation of a $^{78}$Kr beam allowed the observation of new neutron-deficient isotopes at the proton drip-line. Clean identification spectra could be produced and $^{63}$Se, $^{67}$Kr, and $^{68}$Kr were identified for the first time. In addition, $^{59}$Ge was also observed. Three of these isotopes, $^{59}$Ge, $^{63}$Se, and $^{67}$Kr, are potential candidates for ground-state two-proton radioactivity. In addition, the isotopes $^{58}$Ge, $^{62}$Se, and $^{66}$Kr were also sought but without success. The present experiment also allowed the determination of production cross sections for some of the most exotic isotopes. These measurements confirm the trend already observed that the empirical parameterization of fragmentation cross sections, EPAX, significantly overestimates experimental cross sections in this mass region.

High-spin states in 78Kr and 76Kr were studied via the reactions 58Ni( 24Mg, 4p) 78Kr and 58Ni( 24Mg, α2p) 76Kr at 110 MeV beam energy. An array of fifteen Compton suppressed Ge detectors was used in the POLYTESSA framework to collect γγ-coincidence spectra. Rotational bands were observed up to probable spins of 24 + and 22 − in 76Kr, and 24 + and 21 in 78Kr. While the positive-parity yrast bands show strong variations in the moments of inertia caused by the alignments of pairs of ( g 9 2 ) proton and neutron quasiparticles, the negative-parity bands display a constant moment of inertia throughout most of their frequency range. The band crossings and alignments in both nuclei are discussed in the context of the cranked shell model. From an examination of the systematics of crossing frequencies along the Kr isotopes, the previous suggestion that protons align first is confirmed. The intrinsic structures of the bands are also analyzed with the Woods-Saxon-Strutinsky cranking model. The interplay between neutron and proton excitations, the shape changes induced by quasiparticle alignment, and the possible reduction of the static proton pairing in the negative-parity bands are discussed in detail. Three lifetimes in the 76Kr ground band were remeasured by using the Doppler shift attenuation method, indicating a constant deformation of β 2 = 0.33 up to spin 10 +.

States in 162Dy have been populated by ( n , γ ) , ( n , e − ) , and ( α , 2 n ) reactions in order to characterize a complete set of low K bands below 2 MeV. The ( n , γ ) and ( n , e − ) measurements were made using high precision curved crystal and β − spectrometers. Gamma–gamma coincidence and DCO measurements were made following the ( α , 2 n ) reaction using an array of Compton-suppressed Ge detectors. Using all these data and employing the Ritz combination principle, a level scheme was developed which represents one of the most complete and extensive spectra of levels available for comparison with nuclear models. The observed positive and negative parity bands are discussed in terms of collective quadrupole and octupole vibrational excitations as well as 2 quasi-particle excitations.

Measurements of the conversion electron spectrum from the 167Er(n, e −) 168Er reaction show L I L III = 0.0859(6) , L II L III = 0.963(4) , M I M III = 0.696(7) , and M II M III = 0.934(5) for the 79.804 keV, 2 + → 0 +, E2 transition and L I L III = 0.663(4) , L II L III = 1.270(6) for the 184.285 keV, 4 + → +, E2 transition in 168Er. For the 79.8 keV transition the L II L III ratio is (5.7 ± 0.7)% higher and the M I M III ratio (7.0 ± 1.1)% lower than predicted by theory. The L II L III and M II M III ratios for this transiton and the L-subshell ratios of the 184 keV transition agree with the theory. An explanation of the observed discrepancies is sought in the sensitivity of the calculated L I and M I conversion coefficients on the lower energy region to a partical cancellation in the leading matrix element for E2 conversion.

The properties of the low-lying positive parity states of 160 70Yb 90 are reported and compared with predictions of the IBA-2 model based on parameters extrapolated from earlier calculations on the lighter, N = 90 isotones. There is good agreement between theory and experiment. The results confirm the predicted transition between the SU(3) and O(6) limits of the IBA for the N = 90 isotones, and point to a new region of O(6) symmetry.

The efficiency of the NPL magnetic β-ray spectrometer has been increased by a factor ∼ 240 so that the decay of long-lived actinide nuclei may be studied. This large increase in efficiency was achieved by the use of a large area multistrip source in the manner of Bergkvist, together with the development of a sixteen element proportional counter. These modifications to the β-ray spectrometer have permitted the study of internal conversion following the decay of 237Np. The low-energy scheme of 233Pa has been determined on the basis of these measurements and the results of complementary singles and coincidence γ-ray studies.

The low-lying, rotational band structures of the highly neutron-deficient light rare-earth nuclei, 133Sm and 133Pm have been investigated using the 40Ca + 96Ru reaction at a beam energy of approximately 180 MeV. Five new bands have been observed in both nuclei. 133Sm possesss two strongly coupled bands which are thought to be built upon the vh112[523]72−and vd52[402]52+ Nilsson configurations. In addition to the previously reported vi132 intruder band, there is also evidence for a second decoupled, negative-parity structure in 133Sm based on the vh92[541]12− orbital. In 133Pm evidence is presented for both signature partners of the πh112 band. The expected h112 neutron alignment in these bands has not been observed. It is suggested that this provides evidence for a strong pn interaction. A strongly coupled band built on the πg72[413]52+ configuration has also been established. Both signature partners of this band show clear evidence for the alignment of a pair of h112 protons followed by a pair of h112 neutrons. A strongly coupled three quasi-particle configuration has also been identified which feeds into the unfavoured signature of the πh112 band. The results are discussed in terms of cranked shell model, total routhian surface calculations and the systematics of the A ∼ 135 region.

The 28Si( 58Ni, 2n) 84Mo reaction has been studied at 195 MeV bombarding energy. The prompt gamma rays were detected in an array of twenty, escape-suppressed Ge detectors in coincidence with the recoiling nuclei, which were identified by A and Z with a recoil separator. A 443.8±0.3 keV gamma ray was observed from 84Mo which is interpreted as the 2 +−0 + transition in this nucleus. This would indicate a quadrupole deformation ε 2∼0.30. This result confirms that 76Sr lie at the centre of the region of deformed nuclei with A∼80.

The gamma decays of excited states in the nucleus 126Ce have been identified in a study of the 92Mo( 40Ca, α2p) 126Ce reaction at 150–200 MeV bombarding energy using multiple particle-gamma coincidence techniques. Measurements were made of gamma-ray angular distributions and production cross sections as a function of energy. The lifetimes of the lowest states in the ground state band of 126Ce were measured using the recoil distance method. The first excited state was found to have a meanlife of τ m = 949 ± 53 ps, which is consistent with a ground state quadrupole deformation of ε 2 = 0.28 ± 0.01 assuming axial symmetry and a uniform charge distribution. In the ground state rotational sequence a backbend is observed at h ̵ w c ≏ 0.32 MeV . This appears to be due to the alignment of h 11 2 protons. These properties are compared with the results of potential energy surface and cranked shell model calculations and are assessed in the context of the systematic behaviour of even-even nuclei in this mass region.

Levels in the 75Kr nucleus were populated in the inverse 24Mg( 54Fe, 2pn) 75Kr reaction at beam energies of 177 and 190 MeV. In the reaction study at 177 MeV, the γ-rays were detected in coincidence with neutrons and mass-75 nuclei and in the reaction at 190 MeV only γγ-coincidence data were collected. Using the γγ-neutron gated γγ- and Recoil-γγ-coincidence techniques, we were able to develop the level scheme up to spins ( 37+ 2 ) and ( 31− 2 ) in the positive- and negative-parity bands, respectively. These spins are high enough to allow us to study alignment effects in this mass region. The signature splitting at low spin can be reproduced in a cranked shell model calculation assuming a quadrupole deformation β 2 = 0.37 and a slightly triaxial ( γ≈ −10°) shape for positive-parity states but an axial shape for the negative-parity sequence. The spin alignment as a function of rotational frequency has been studied; in the positive-parity band alignment is observed at a rotational frequency of h ̵ ω ≈ 0.63 MeV and in the negative-parity band the alignment occurs at h ̵ ω ≈ 0.57 MeV . The observed alignment in both bands is associated with a pair of g 9 2 protons, and the difference in the alignment frequencies is thought to be due to differing intrinsic shapes.

Nuclei near the prolate single-particle energy gap at proton number Z = 38 ( ε 2 ≈ +0.38) and neutron number N ≈ Z offer unique possibilities to study the pn-interaction at large quadrupole deformation. In the yrast band of the Z = N = 37 nucleus 74Rb, we have identified a crossing of the T = 1 pn-paired band (even spins) with the T = 0 pn-unpaired band (odd spins). In 77Rb, the positive-parity yrast and yrare bands have been followed over large spin ranges and assigned different 1qp-proton 2qp-neutron structures. These band crossings do not follow the usual pattern of two identical particles aligning in high-j orbits. In addition, an aligned g 9 2 proton-neutron negative-parity sequence with K= 11 2 has been identified in 77Rb Rotational bands with more conventional band crossings have also been found.

Electric monopole transitions in 172Yb and 174Yb have been studied following thermal neutron capture on 171Yb and 173Yb. It is found that the second excited 0 + state in 172Yb at 1405 keV has a very large X = B( E0; 0 2 +−0 g +) B( E2; 0 2 +−2 g + value of 2.81±0.31. The E0 decay branches for the other 0 + states in 172Yb were also measured. In the case of 174Yb no E0 conversion lines were observed from the corresponding 0 + states but upper limits were placed on their intensities. These results indicate that none of the known 0 + states in 174Yb exhibit such a large X-value. Various interpretations are discussed and it is concluded that the 1405 keV level in 172Yb may contain large amplitudes of proton pair excitations. A model based on such excitations is presented which accounts qualitatively for the large X(1405) value in 172Yb as well as for the systematics of large X-values in the rare-earth region.

The structure of 72Kr has been investigated at GASP through the 40Ca( 40Ca,2α) reaction at a beam energy of 160 MeV using the 4π ISIS Si-ball for reaction channel selection. The level scheme has been extended up to an excitation energy of ≈ 8.5 MeV. The spins and parties of the observed levels are assigned tentatively. The observed band shows the predicted change from oblate to prolate shape. The four quasi-particle g 9 2 alignment is found to be significantly delayed in rotational frequency with respect to the heavier Kr isotopes. Such a delay contradicts the predictions of standard mean-field calculations and may reflect either additional correlations in the T = 0 pairing channel or coupling to vibrational degrees of freedom or both.

The high-spin structure of 79Rb was studied via the 24Mg( 58Ni, 3p) reaction at 190 MeV, using a Compton suppressed germanium detector array and the Daresbury Recoil Separator. The two signatures of a positive-parity, decoupled g 9 2 quasiparticle band were followed up to spins 41 2 and 35 2 , respectively. Similarly the two signatures of a negative-parity, decoupled ( f 5 2 , P 3 2 ) band were identified up to the same spin values. A weakly populated level sequence with the character of a coupled quasi-rotational band is tentatively suggested. The band structures are analyzed in terms of the cranked shell model.

The neutron-deficient isotope 32 64Ge 32 was produced in the reaction 12C( 54Fe, 2nγ) 64Ge at a beam energy of 165 MeV. The production cross section for 64Ge was measured to be 640 ± 70 μb, which represents only ∼0.1% of the total fusion cross section. The Daresbury recoil separator was operated in conjunction with a large γ-array to study recoil-γγ correlations and measure recoil-γ angular distributions. A level scheme for 64Ge was constructed containing 19 levels. The nucleus appears to have a structure consistent with a γ-soft shape. Shape changes induced by aligned g 9 2 nucleons are discussed. An overview of octupole correlations in the A ⋍ 60−80 mass region is given. Evidence for forbidden E1 transitions was found which is indicative of considerable isospin mixing.

New results for the Coulomb energy differences in the A=47 mirror nuclei 47Cr and 47V for yrast states up to spin 31 2 ℏ are presented and shown to agree with earlier predictions made within a deformed, crancked shell model approach. The observed total difference in Coulomb displacement energies at low and high angular momenta is also explained within the spherical shell model. The first example of alignment in an N= Z nucleus, 48Cr, is reported.

The M1 strength in a number of γ → g transitions in 168Er have been determined from high-precision L-subshell conversion electron intensity measurements. The results are combined with earlier data for transitions within the γ-band and compared with the predictions of an IBA-2 calculation. It is shown that a satisfactory description of both E2 and M1 properties can be obtained with the appropriate degree of F-spin symmetry breaking in the hamiltonian, which in turn relates to the degree of neutron-proton symmetry in the collective wavefunction.

The level scheme of 87Mo was investigated with the reaction 58Ni( 32S, 2pn) at projectile energies of 110–130 MeV and the reaction 40Ca( 50Cr, 2pn) at 170 MeV. Extensive spectroscopic information was collected including γγ and neutron-gated γγ coincidences as well as coincidences with identified 87Mo residues. Level lifetimes were studied with the RDDS and DSA methods. The angular distributions of low-lying transitions were measured. The results indicate a sudden transition from single-particle-like to collective behavior which is caused by g 9 2 particle alignment. The level scheme was constructed up to 12 MeV excitation energy and a probable spin of 40 2 h ̵ .

A measurement of the cumulated beta spectrum from 235U fission products was performed with a magnetic spectrometer. The energy range 2.0–9.5 MeV was covered achieving a sensitivity of 3 x 10 −6 betas per MeV per fission in the high energy region. The absolute rates were calibrated with a precision of 3%. The beta spectrum was converted into the correlated ν e spectrum to provide a basis for antineutrino experiments at nuclear reactors.

Even mass neutron-rich niobium isotopes are among the principal contributors to the reactor antineutrino energy spectrum. They are also among the most challenging to measure due to the refractory nature of niobium, and because they exhibit isomeric states lying very close in energy. The β-intensity distributions of Nb100gs,100m and Nb102gs,102m β decays have been determined using the total absorption γ-ray spectroscopy technique. The measurements were performed at the upgraded Ion Guide Isotope Separator On-Line facility at the University of Jyväskylä. Here, the double Penning trap system JYFLTRAP was employed to disentangle the β decay of the isomeric states. The new data obtained in this challenging measurement have a large impact in antineutrino summation calculations. For the first time the discrepancy between the summation model and the reactor antineutrino measurements in the region of the shape distortion has been reduced.

The reaction {sup 40}Ca+{sup 12}C at {ital E}{sub Ca}=160 MeV has been used to study high-spin states in the recoil-separated nuclides {sup 49}Cr, {sup 49}V, and {sup 46}Ti. The latter two show distinctive {ital f}{sub 7/2} shell-model behavior up to {ital J}{sup {pi}}=27/2{sup {minus}} and 12{sup +}, respectively, while the first appears to be a collective rotor with a particle alignment at {ital J}{sup {pi}}=17/2{sup {minus}}. Rotorlike bands of {ital sd}-shell origin were seen in {sup 49}V and {sup 46}Ti up to {ital J}{sup {pi}}=11/2{sup +} and 11{sup {minus}}, respectively.

Gamma rays from the reaction 28Si( 58Ni, 3p) 83Y at a beam energy of 195 MeV were recorded in recoil-γ- and γγ-coincidence mode with the POLYTESSA array and the Daresbury recoil mass separator. The known rotational bands were extended up to probable spins 49+ 2 and 45− 2 ; many new interconnecting dipole transitions and an additional cascade were established. The bands are interpreted in terms of the cranked shell model; they exhibit two band crossings each, associated with g 9 2 neutron and proton alignment. In the negative-parity yrast bands a strong signature inversion with Δe′=−100 keV and a crossing pattern alternating in the favoured and unfavoured band develop. Hartree-Fock-Bogolyubov cranking calculations with a Woods-Saxon single-particle potential have been performed to illustrate the various shape changes and explain this signature inversion.

We report on the observation of excited states in the niobium isotope with masses 84, 85 and 86. These nuclei lie in the shape transition region known to occur in nuclei with 35⩽ Z⩽40 and N=45. Unambiguous identification was achieved by detecting γ-rays in coincidence with mass-separated recoils produced in heavy-ion fusion reactions. Rotational bands were observed in 84Nb and 85Nb which show decoupling schemes similar to those in the neighbouring nuclei. A rotational model was used to interpret these bands and the quasiparticle configurations involved. Two sequences of transitions were observed in 86Nb, at least one of which appears to be a rotational band.

High-spin states in the nuclei {sup 47}Ti, {sup 47}V, {sup 47}Cr, {sup 48}V, and {sup 48}Cr have been observed using the reaction {sup 40}Ca+{sup 10}B at {ital E}({sup 40}Ca)=150 MeV. The prompt {gamma} rays were detected in an array of nineteen escape-suppressed Ge detectors in coincidence with the recoiling nuclei which were identified in {ital A} and {ital Z} with a recoil separator. Rotational structures were observed in all these nuclei, apart from {sup 47}Ti, up to spins near the maximum for the ({ital f}{sub 7/2}){sup {ital z}+{ital n}} configuration. A rapid increase in the Coulomb displacement energy for mirror states in {sup 47}V and {sup 47}Cr occurs at {ital J}{sup {pi}}=25/2{sup {minus}}. A backbend occurs in {sup 48}Cr at {ital J}{sup {pi}}=10{sup +}.

The antineutrino spectrum of fission products from thermal neutron induced fission of 241Pu was derived from a measurement of the correlated beta spectrum. The energy range 1.5 MeV to 9 MeV was covered and a precision of 4% was achieved at 4 MeV. A revised version of the antineutrino spectrum from 239Pu fission is also presented.

The L-subshell conversion line intensity ratios of five pure M1 transitions have been measured with the Chalk River iron-free, π√2 β-spectrometer at momentum resolutions ranging from ≈ 0.04% to 0.19%. The transition energies in keV and the L I/L II and L I/L III ratios for the cases studied are 144 Pr, 80.12, 12.2 ± 0.3, 59.6 ± 3.0; 144 Pr, 133.53, 13.4 ± 0.2, 64.3 ± 1.7; 166 Ho, 82.45, 11.4 ± 0.2, 72.3 ± 1.1; 210 Bi, 46.503, 9.67 ± 0.13, 115 ± 3; 212 Bi, 238.6, 9.36 ± 0.13, 133.5 ± 6 . The results have been compared with theoretical ratios deduced from the tabulations of Rose, Sliv and Band, Pauli, and Hager and Seltzer. These comparisons reveal significant discrepancies between the theoretical ratios of Rose and experiment for these M1 transitions. The theoretical ratios of Sliv and Band, Pauli, and Hager and Seltzer agree well among themselves and with experiment. The experimental ratios are found to be in best agreement with the theoretical ratios of Sliv and Band and of Pauli which take account of the contribution of the dynamic nuclear penetration effect to the internal conversion coefficient, but the experimental accuracies, which range from 2–4%, are not sufficient to allow an unqualified conclusion concerning the validity of this small correction. The L-subshell conversion ratios of the 59.03 keV, pure M3 (3 − → 0 −) transtion in 144Pr were also measured (see appendix) and found to be L I/L II = 6.43 ± 0.32 andL I/L III = 0.662 ± 0.008. These ratios are in agreement with theory.

The electromagnetic decay properties of levels in 100Mo have been studied by Coulomb-excitation yield measurements and lifetime determinations. For the yield measurements thin targets of 100Mo were bombarded with beams of 16O and 32S at 42 and 89 MeV incident energy, respectively. The emitted γ-rays were observed in coincidence with particles detected in a position-sensitive gas proportional counter. In a separate experiment the recoil-distance method was used to determine the lifetimes of levels in 100Mo excited in the bombardment of a thin target with a 58Ni beam of 185 MeV energy. Matrix elements for the observed transitions were deduced from the particle-gamma coincidence yields and from the measured lifetimes. A consistent set of results was obtained. The collective E2 transition rates determined from the analysis were found to be in remarkably good agreement with the predictions of the interacting boson model with configuration mixing.

In a search for predicted effects of the neutron-proton interaction, the g factors of states in the yrast band of 84Zr have been measured up to spin 14ħ using the transient field technique. The measurement probes the region through the first observed alignment at a crossing frequency of 0.48 MeV/ħ. The results clearly demonstrate that the aligning particles are protons rather than a superposition of aligned protons and neutrons as previously suggested; n-p correlations do not appear to influence the nature of the alignment in this nucleus.

The Coulomb excitation of 195Pt has been measured using α-particles of energy 5.6 to 6.5 MeV. Angular distributions were obtained for a number of transitions. The deduced B(E2) values are compared with the predictions of the O(6) boson-fermion symmetry scheme. The comparison indicates a number of discrepancies, some of which can be explained by considering the semi-microscopic form of the E2 operator. The observed decay of one level, however, remains inconsistent with the predictions of the symmetry scheme.

Gamow-Teller (GT) transitions can be studied in both beta decay and charge exchange (CE) reactions. If isospin is a good quantum number, then the Tz = -1 -> 0 and Tz = +1 -> 0 GT mirror transitions, are identical. Therefore, a comparison of the results from studies of beta decay and CE should shed light on this assumption. Accordingly we have studied the beta decay of the Tz = -1 fp-shell nuclei, Ni-54, Fe-50, Cr-46, and Ti-42, produced in fragmentation and we have compared our results with the spectra from (He-3, t) measurements on the mirror Tz = +1 target nuclei studied in high resolution at RCNP, Osaka. The beta decay experiments were performed as part of the STOPPED beam RISING campaign at GSI.

The excited states of the proton emitter Lu-151 were reinvestigated in a recoil-decay tagging experiment at the Accelerator Laboratory of the University of Jyvaskyla (JYFL). The level scheme built on the ground state of 151Lu was updated with five new y-ray transitions. Large-scale shell model calculations were carried out in the model space consisting of the neutron and proton orbitals 0g(7/2), Id(5/2), Id(3/2), 2s(1/2), and Oh(1/2) with the optimized monopole interaction in order to interpret the experimental level scheme of Lu-151. It is found that the excitation energies of states above the 27/2(-) and 23/2(+) isomeric levels in Lu-151 can be sensitive to excitations from g(7/2) and d(5/2) to single-particle orbitals above N = Z = 64.

Remarkable results have been published recently on the beta decay of Zn-56. In particular, the rare and exotic beta-delayed gamma-proton emission has been detected for the first time in the fp shell. Here we focus the discussion on this exotic decay mode and on the observed competition between beta-delayed protons and beta-delayed gamma rays from the Isobaric Analogue State.

In this lecture the development of arrays of γ-ray detectors is described. The starting point is the reason why we want to study γ-rays emitted in nuclear reactions. An account of how gamma rays interact with matter follows. The characteristics of the γ-ray detectors needed for the study of both exotic nuclei and high spin states are then outlined. The development of γ-rays arrays is followed up to the present introduction of detectors based on gamma-ray tracking. Examples taken from experiment are used throughout.

Studying weak nuclear responses, especially the Gamow-Teller (GT) transitions starting from stable as well as unstable nuclei, provide crucial and critical information on nuclear structure. Therefore, the study of GT transitions is a key issue in nuclear physics and also nuclear-astrophysics. Under the assumption of isospin symmetry, it is expected that the structure of mirror nuclei and the GT transitions starting from their ground states are identical. We have studied the corresponding GT transitions starting from T-z = +/- 1 and +/- 2 p f -shell nuclei, respectively, by means of hadronic (He-3,t) charge-exchange reactions and mirror beta decays. The results on GT strength distributions measured in beta decays and (He-3,t) reactions performed at an intermediate incident energy of 140 MeV/nucleon and 0 degrees are compared. The combined results help provide an understanding of nuclear structure of nuclei far-from-stability.

The results of a study of the beta decays of three proton-rich nuclei with T-z = -2, namely Fe-48, Ni-52, and Zn-56, produced in an experiment carried out at GANIL, are reported. In all three cases we have extracted the half-lives and the total beta-delayed proton emission branching ratios. We have measured the individual beta-delayed protons and beta-delayed. rays and the branching ratios of the corresponding levels. Decay schemes have been determined for the three nuclei, and new energy levels are identified in the daughter nuclei. Competition between beta-delayed protons and. rays is observed in the de-excitation of the T = 2 isobaric analog states in all three cases. Absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. In addition, we discuss in detail the data analysis taking as a test case Zn-56, where the exotic beta-delayed gamma-proton decay has been observed.

Gamow-Teller (GT) transitions can be studied in both beta- decay and charge exchange(CE) reactions. If isospin is a good quantum number, then the Tz = -1 -> 0 and Tz = +1 -> 0 GT mirror transitions, are identical. Therefore, a comparison of the results from studies of beta decay and CE should shed light on this assumption. Accordingly we have studied the beta decay of the Tz = -1 fp-shell nuclei, Ni-54, Fe-50, Cr-46, and Ti-42, produced in fragmentation and we have compared our results with the spectra from (He-3, t) measurements on the mirror Tz = +1 target nuclei studied in high resolution at RCNP, Osaka. The beta- decay experiments were performed as part of the STOPPED beam RISING campaign at GSI

The decay heat of fission products plays an important role in predictions of the heat released by nuclear fuel in reactors. In this contribution we present results of the analysis of the measurement of the beta decay of some refractory isotopes that were considered possible important contributors to the decay heat in reactors. The measurements presented here were performed at the IGISOL facility of the University of Jyvaskyla, Finland. In our measurements we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed.

Mean lifetimes of high-spin states of Kr-74 have been determined using the Doppler-shift attenuation method. The high-spin states were studied using the Ca-40(Ca-40, alpha 2p) reaction at a beam energy of 160 MeV with the GASP gamma-ray spectrometer. The ground-state band and negative parity side band show the presence of three different configurations in terms of transitional quadrupole deformations. A dramatic shape change was found along the ground-state band after the S-band crossing. The deduced quadrupole deformation changes are well reproduced by cranked Woods-Saxon Strutinsky calculations.

Three observables of interest for present and future reactors depend on the β decay properties of the fission products: antineutrinos from reactors, the reactor decay heat and delayed neutron emission. In these proceedings, we present new results from summation calculations of the first two quantities quoted above, performed with evolved independent yields coupled with fission product decay data, from various nuclear data bases or models. New TAGS results from the latest experiment of the TAGS collaboration at the JYFL facility of Jyväskylä will be displayed as well as their impact on the antineutrino spectra and the decay heat associated to fission pulses of the main actinides.

A study of the Gamow-Teller strength distributions B(GT) in the beta decay of Sr-78 and Rb-76,Rb-78 has been made using a total absorption spectrometer (TAS). Following the success in deducing the sign of the deformation for Sr-76, a similar approach is adopted for Sr-78 based on a comparison of the measured B(GT) with quasiparticle random-phase approximation calculations. This work confirms its previously expected prolate deformation in the ground state. Conclusions about the structure of the odd-odd Rb-76,Rb-78 isotopes have been drawn based on their measured B(GT) distributions.

Gamow-Teller (GT) transitions starting from unstable pf-shell nuclei play important roles in neutrino-induced reactions that happen under the extremely high temperature conditions in core-collapse (type 11) supernovae. In the 0 decay, it is difficult to obtain GT strengths B(GT) to higher excited states, but accurate half-lives can be measured. On the other hand, high-resolution (He-3,t) charge-exchange reactions at 0 degrees and at 420 MeV yield cross-sections, that are proportional to B(GT) values, for individual transitions up to high excitation. Assuming isospin symmetry, we performed a unique analysis to determine absolute B(GT) values for the T-z = +/-1 --> 0 analogous GT transitions. Further P-decay studies for unstable pf-shell nuclei to obtain accurate half-lives and feeding ratios are in progress.

Gamma-ray spectra of neutron-deficient isotopes between Ce (Z = 58) and Gd (Z = 64) have been investigated. New bands of states were identified in many even--even, odd--A, and odd--odd nuclei. Results on the ground-state bands in the even--even nuclei exp 126 sub 58 Ce sub 68 , exp 128,130,132 sub 60 Nd sub 68,70,72 , exp 134,136 sub 62 Sm sub 72,74 , and exp 138,140 sub 64 Gd sub 74,76 are reported. The systematic trends of deformation are presented and compared with theoretical predictions. The lightest isotopes appear to be axially symmetric rotors with epsilon sub 2 = > 0.3. 22 ref.--AA

The two-proton radioactivity is a unique tool to study the nuclear structure beyond the proton drip-line. Since its discovery in 2002, the known emitters have been Mg-19, Fe-45, Ni-48, Zn-54 and Kr-67. Kr-67 was observed for the first time at the RIKEN Nishina Center in 2015. Its decay energy was measured at 1690(17) keV with a branching ratio of 37(14) %. The halflife, 7.4(30) ms, was found in contradiction with theoretical calculations, pointing out effects of decay dynamics and nuclear deformation.

Issues concerning the management of the UK's official radioactive wastes and associated surplus radioactive materials are summarised. The potential for partitioning and transmutation (P& T) of these materials is considered and associated potential developments discussed. The paper recommends international P& T research as part of a move to reduce the volume of nuclear waste. This reduction would be beneficial in addressing security and environmental concerns, as well as improving public acceptance of the back-end of the nuclear fuel cycle.

The energy associated with the decay of fission products plays an important role in the estimation of the amount of heat released by nuclear fuel in reactors. In this article we present results of the study of the beta decay of some refractory isotopes that were considered important contributors to the decay heat in reactors. The measurements were performed at the IGISOL facility of the University of Jyvaskyla, Finland. In these studies we have combined for the first time a Penning trap (JYFLTRAP), which was used as a high resolution isobaric separator, with a total absorption spectrometer. The results of the measurements as well as their consequences for decay heat summation calculations are discussed.

The beta-delayed neutron emission probability, P-n, of very neutron-rich nuclei allows us to achieve a better understanding of the nuclear structure above the neutron separation energy, S-n. The emission of neutrons can become the dominant decay process in neutron-rich astrophysical phenomena such as the rapid neutron capture process (r-process). There are around 600 accessible isotopes for which beta-delayed one-neutron emission (beta 1n) is energetically allowed, but the branching ratio has only been determined for about one third of them. beta 1n decays have been experimentally measured up to the mass A similar to 1 5 0, plus a single measurement of Tl-210. Concerning two-neutron emitters (beta 2n), similar to 3 0 0 isotopes are accessible and only 24 have been measured so far up to the mass A = 100. In this contribution, we report recent experiments which allowed the measurement of beta 1n emitters for masses beyond A > 200 and N > 1 2 6 and identified the heaviest beta 2n emitter measured so far, Sb-136.

The beta (+) -decay half-lives of the neutron-deficient odd-odd N=Z nuclei Rb-74, Y-78, Nb-82, and Tc-86 have been measured following the fragmentation of a primary Mo-92 beam at an energy of 60 MeV per nucleon at the GANIL laboratory, France. This was achieved by correlating beta (+) decays with the implantation of unambiguously identified fragments at the final focus of the LISE3 separator. The deduced log(10)ft(1/2) values are consistent with 0(+)-->0(+). Fermi superallowed transitions, which together with the measured beta (+)-detection efficiencies, suggest T=1, I-pi=0(+) ground states for these odd-odd N=Z nuclei. These data represent the heaviest N=Z systems for which Fermi superallowed decays have been established.

This paper concerns the experimental study of the beta decay properties of few proton-rich fp-shell nuclei. The nuclei were produced at GANIL in fragmentation reactions, separated with the LISE spectrometer and stopped in an implantation detector surrounded by Ge detectors. The beta-delayed gammas, beta-delayed protons and the exotic beta-delayed gamma-proton emission have been studied. Preliminary results are presented. The decay of the T-z = -2 nucleus Zn-56 has been studied in detail. Information from the beta-delayed protons and beta-delayed gammas has been used to deduce the decay scheme. The exotic beta-delayed gamma-proton decay has been observed for the first time in the fp-shell. The interpretation of the data was made possible thanks to the detailed knowledge of the mirror Charge Exchange (CE) process and the gamma de-excitation of the states in Co-56, the mirror nucleus of Cu-56.

Neutron-deficient nuclei close to the proton drip-line have been studied intensively in recent years. Measurements of ground-state proton emitters have mapped out the limits of nuclear stability above 100Sn. Suchexperiments have allowed us to learn about the single-particle shell structure far from stability. Studies of γ-rays from N=Z nuclei produced in fusion-evaporation reactions have revealed that their properties vary rapidly with small changes in Z, N and A because of large oblate and prolate shell gaps at large deformation. Studies of these nuclei also reveal information about isospin mixing as a function of mass and potentially yield information about n-p pairing. The astrophysical rp-process pathway lies close to the N=Z line. Studies of fragmentation reactions have allowed us to determine a lot of the information needed to analyse the rp-process in detail. All of this information is limited, however, by the constraint of using stable beams and targets. With beams of radioactive nuclei, classical spectroscopic techniques such as Coulomb excitation and particle transfer studies will allow us to map out level properties in detail in nuclei far from stability. Studies of fusion-evaporation reactions with beams of radioactive ions by using new, more sensitive detection techniques will allow us to study nuclei up to and beyond the drip-line in nuclei above 100Sn. At the same time such studies will allow us much greater access to the lighter N=Z nuclei.

The K conversion coefficients of transitions of 1–9 MeV in 114Cd were determined by combining measured relative intensities of the γ rays with the conversion-electron data of Von Egidy and Kaiser. These coefficients disagree with those reported by Smither, but agree with recent theoretical estimates.

Beta decay of fission products is at the origin of decay heat and antineutrino emission in nuclear reactors. Decay heat represents about 7% of the reactor power during operation and strongly impacts reactor safety. Reactor antineutrino detection is used in several fundamental neutrino physics experiments and it can also be used for reactor monitoring and non-proliferation purposes. Rb-92,Rb-93 are two fission products of importance in reactor antineutrino spectra and decay heat, but their beta-decay properties are not well known. New measurements of Rb-92,Rb-93 beta-decay properties have been performed at the IGISOL facility (Jyvaskyla, Finland) using Total Absorption Spectroscopy (TAS). TAS is complementary to techniques based on Germanium detectors. It implies the use of a calorimeter to measure the total gamma intensity de-exciting each level in the daughter nucleus providing a direct measurement of the beta feeding. In these proceedings we present preliminary results for Rb-93, our measured beta feedings for Rb-92 and we show the impact of these results on reactor antineutrino spectra and decay heat calculations.

In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton (2p) emission from Kr-67. At the same time, no evidence for 2p emission of Ge-59 and Se-63, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with Q value predictions which pointed to Kr-67 as being the best new candidate among the three for two-proton radioactivity. Kr-67 is only the fourth 2p ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the 2p emission branching ratio is 37(14)%, and the half-life of Kr-67 is 7.4(30) ms.

The first experiments performed using fast fragmentation beams and the RISING gamma-ray spectrometer are reviewed and their results are discussed. Plans for future campaigns using ions which are slowed down and stopped in a catcher will also be presented, including details of experiments which measure magnetic moments (g-factor) and beta decays using an active stopper.

The reactions 52Cr + 96Ru at 240 MeV, 56Fe + 92Mo at 250 MeV and 54Fe + 92Mo at 260 MeV have been used to form the compound nuclei 146, 148Er. Bands of gamma ray transitions were identified as belonging to the odd-proton nuclei 137Eu, 141, 143, 145Tb and 145Ho which are among the decay products of these compound systems. The observed level sequences closely resemble the ground state bands in the neighbouring, even-even core nuclei, and appear to be rotationally aligned bands based on the h 11 2 proton orbit. In all the cases reported these are the first data on excited states.

Gamow-Teller (GT) transitions are the most common weak interaction processes of spin-isospin (sigma tau) type in atomic nuclei. They are of interest not only in nuclear physics but also in astrophysics; they play an important role in supernovae explosions and nucleosynthesis. The direct study of weak decay processes, however, gives relatively limited information about GT transitions and the states excited via GT transitions (GT states); beta decay can only access states at excitation energies lower than the decay Q-value, and neutrino-induced reactions have very small cross-sections. However, one should note that beta decay has a direct access to the absolute GT transition strengths B(GT) from a study of half-lives, Q(beta)-values and branching ratios. They also provide information on GT transitions in nuclei far-from-stability. Studies of M1 gamma transitions provide similar information. In contrast, the complementary charge-exchange (CE) reactions, such as the (p, n) or (He-3, t) reactions at intermediate beam energies and 0 degrees, can selectively excite GT states up to high excitation energies in the final nucleus. It has been found empirically that there is a close proportionality between the cross-sections at 0 degrees and the transition strengths B(GT) in these CE reactions. Therefore, CE reactions are useful tools to study the relative values of B(GT) strengths up to high excitation energies. In recent (He-3, t) measurements, one order-of-magnitude improvement in the energy resolution has been achieved. This has made it possible to make one-to-one comparisons of GT transitions studied in CE reactions and beta decays. Thus GT strengths in (He-3, t) reactions can be normalised by the beta-decay values. In addition, comparisons with closely related M1 transitions studied in gamma decay or electron inelastic scattering [(e, e')1, and furthermore with "spin" M I transitions that can be studied by proton inelastic scattering [(p, p')[ have now been made possible. In these comparisons, the isospin quantum number T and associated symmetry structure in the same mass A nuclei (isobars) play a key role. Isospin symmetry can extend our scope even to the structures of unstable nuclei that are far from reach at present unstable beam factories. (C) 2011 Elsevier B.V. All rights reserved.

The beta decay of Pb-192,Pb-190 has been studied using the total absorption technique at the ISOLDE (CERN) facility. The beta-decay strength deduced from the measurements, combined with QRPA theoretical calculations, allow us to infer that the ground states of the Pb-192,Pb-190 isotopes are spherical. These results represent the first application of the shape determination method using the total absorption technique for heavy nuclei and in a region where there is considerable interest in nuclear shapes and shape effects.

The beta decay of the Tz=-2 nucleus 64Se has been studied in a fragmentation reaction at RIKEN-Nishina Center. 64Se is the heavies Tz=-2 nucleus that decays to bound states in the daughter nucleus and the heaviest case where the mirror reaction 64Zn(3He,t)64Ga on the Tz=+2 64Zn stable target exists and can be compared. Beta-delayed gamma and proton radiation is reported for the 64Se and 64As cases. New levels have been observed in 64As, 64Ge (N=Z), 63Ge and 63Ga. The associated T1/2 values have been obtained.

The very neutron-deficient isotope Cd-102 was produced in the reaction Cr-50(Fe-56, 2p2n) Cd-102 at 195 MeV and was identified using the Daresbury recoil separator. A pure gamma-ray spectrum belonging to the de-excitation of the excited states of Cd-102 was obtained in-beam. Twenty gamma-ray lines were identified, ten of them for the first time. The intensity balance concerning some of these gamma-rays together with the results obtained from the coincident measurements show the existence of a new set of levels which may be interpreted as being a side band confirming the coupling of(v)(-2) and (pi)(4) configurations.

We report the first observation of the 2(+) isomer in Co-52, produced in the beta decay of the 0(+), Ni-52 ground state. We have observed three. rays at 849, 1910, and 5185 keV characterizing the beta de-excitation of the isomer. We have measured a half-life of 102(6) ms for the isomeric state. The Fermi and Gamow-Teller transition strengths for the beta decay of Co-52m to Fe-52 have been determined. We also add new information on the beta decay of the 6(+), Co-52 ground state, for which we have measured a half-life of 112(3) ms.

In this contribution we will present recent total absorption measurements of the beta decay of neutron-rich nuclei performed at the IGISOL facility of the Univ. of Jyvaskyla. In the measurements the JYFL Penning Trap was used as a high resolution isobaric separator. The total absorption technique will be described and the impact of recent results in the fields of reactor physics (decay heat calculations) and nuclear structure will be discussed.

The first results from the Stopped Beam RISING experimental campaign performed at the GSI laboratory in Darmstadt, Germany, are presented. RISING (Rare ISotope INvestigations at GSI) constitutes a major new experimental program in European nuclear structure physics research aimed at using relativistic‐energy, projectile‐fragmentation reactions to study nuclei with exotic proton‐to‐neutron ratios. This paper introduces the physics aims of the Stopped RISING collaboration and presents some technical details and initial results from experiments using the RISING array to study decays from metastable nuclear states in both proton and neutron‐rich nuclei.

Studying the weak nuclear response, especially the Gamow-Teller (GT) transitions, of stable as well as unstable pf-shell nuclei, is one of the key issues in nuclear and astro- nuclear physics. We study the decay half-lives and the GT transitions starting from Tz = 1 and 2 mirror nuclei, respectively, by means of decays and complementary hadronic (3He; t) charge-exchange reactions. Under the assumption that isospin is a good quantum number, symmetry is expected for mirror nuclei and the GT transitions starting from the mirror nuclei. The half-lives and branching ratios and the measured strength distributions of GT transitions are compared and also combined for the understanding of the nuclear structure of pf-shell nuclei far-from-stability.

Gamma ray spectroscopy has been one of our main tools for the study of nuclear structure, and will continue to be so with the newly available beams of radioactive ions from fragmentation and ISOL-based facilities. Examples of {gamma}-ray studies at the end of the LISE3 spectrometer at GANIL are described. The likely programme of {gamma}-ray spectroscopy at facilities such as SPIRAL is discussed.

We are entering an era where it will be possible to produce beams of a wide range of radioactive nuclear species. This will transform nuclear physics and nuclear astrophysics and open up new avenues of research incondensed matter science and medical physics.

The heavy odd-odd N = Z nuclei Y-78, Nb-82, Tc-86 have been produced at GANIL by fragmentation of a, 60 MeV/u Mo-92 beam on a natural nicker target. Their lifetime have been measured for the first time, using the identification - implantation and subsequent time correlated beta counting technique at the LISE spectrometer. The obtained half-lives for Y-78, Nb-82, Tc-86 are consistent with the microscopic predictions. These nuclei are good candidates to extend the mass range for the V-ud matrix element evaluation and our experimental results highlight the interest of further investigation of their excited states and beta decay schemes as a function of isospin.

Detailed spectroscopic information on the N similar to 82 nuclei is necessary to benchmark shell-model calculations in the region. The nuclear structure above long-lived isomers in Xe-134 is investigated after multinucleon transfer (MNT) and actinide fission. Xenon-134 was populated as (i) a transfer product in Xe-136 + U-238 and Xe-136 + Pb-208 MNT reactions and (ii) as a fission product in the Xe-136 + U-238 reaction employing the high-resolution Advanced Gamma Tracking Array (AGATA). Trajectory reconstruction has been applied for the complete identification of beamlike transfer products with the magnetic spectrometer PRISMA. The Xe-136 + Pt-198 MNT reaction was studied with the gamma-ray spectrometer GAMMASPHERE in combination with the gas detector array Compact Heavy Ion Counter (CHICO). Several high-spin states in Xe-134 on top of the two long-lived isomers are discovered based on gamma gamma-coincidence relationships and information on the gamma-ray angular distributions as well as excitation energies from the total kinetic energy loss and fission fragments. The revised level scheme of Xe-134 is extended up to an

Gamow-Teller (GT) transitions are the most common weak-interaction processes in the Universe. They play important roles in various processes of nucleosynthesis, for example, in the rapid proton-capture process (rp-process). In the pf-shell region, the rp-process runs through neutron-deficient nuclei with T-z = -2, -1, and 0 mainly by means of GT and Fermi transitions, where T-z is the z component of isospin T defined by T-z = (N = Z)/2. Under the assumption of isospin symmetry, mirror nuclei with reversed Z and N numbers, and thus with opposite signs of T-z, have the same structure. Therefore, symmetry is also expected for the GT transitions starting from and ending up in mirror nuclei. We have been studying the T-z = -2 -> -1 and -1 -> 0 GT transitions in beta decays, while those from stable T-z = +2 and +1 nuclei by means of hadronic (He-3; t) charge-exchange (CE) reactions. The results from these studies are compared in order to examine the mirror-symmetry structure in nuclei. In addition, these results are combined for the better understanding of GT transitions in the pf-shell region.

A detailed study of the positive parity yrast and yrare rotational bands in 77Rb is presented. Using the reaction 40Ca( 40Ca, 3 p) and the EUROGAM I spectrometer, γγγ coincidences enabled us to follow both bands over a large spin range and to measure many E2 strengths. The moments of inertia and transition quadrupole moments indicate that a more deformed band ( ϵ 2 ≈ 0.38) is crossed by a less deformed one ( ϵ 2 ≈ 0.29). Since the yrare band starts at the extremely low spin value of I = 9 2 , the conventional band crossing mechanism of two aligning high- j quasiparticles is excluded. The frequency-dependent equilibrium shapes were calculated with Nilsson-Strutinsky type calculations using a diabatic tracing of configurations near the neutron Fermi level. This is the first observation of such a band crossing.

Background: beta-delayed multiple neutron emission has been observed for some nuclei with A 100 to test the predictions of theoretical models and simulation tools for the decays of heavy nuclei in the region of very neutron-rich nuclei. In addition the decay properties of these nuclei are fundamental for the understanding of astrophysical nucleosynthesis processes such as the r-process and safety inputs for nuclear reactors. Purpose: To determine for the first time the two-neutron branching ratio the P-2n value for Sb-136 through a direct neutron measurement and to provide precise P-1n values for Sb-136 and Te-136. Method: A pure beam of each isotope of interest was provided by the JYFLTRAP Penning trap at the Ion Guide Isotope Separator On-Line (IGISOL) facility of the University of Jyvaskyla Finland. The purified ions were implanted into a moving tape at the end of the beam line. The detection setup consisted of a plastic scintillator placed right behind the implantation point after the tape to register the beta decays and the BELEN detector based on neutron counters embedded in a polyethylene matrix. The analysis was based on the study of the beta- and neutron-growth-and-decay curves and the beta-one-neutron and beta-two-neutron time correlations which allowed us the determination of the neutron branching ratios. Results: The P-2n value of Sb-136 was found to be 0.14(3)% and the measured P-1n values for Sb-136 and Te-136 were found to be 32.2(15)% and 1.47(6)% respectively. Conclusions: The measured P-2n value is a factor 44 smaller than predicted by the finite-range droplet model plus the quasiparticle random-phase approximation (FRDM+QRPA) model used for r-process calculations.

In this work we report on the Monte Carlo study performed to understand and reproduce experimental measurements of a new plastic β-detector with cylindrical geometry. Since energy deposition simulations differ from the experimental measurements for such a geometry, we show how the simulation of production and transport of optical photons does allow one to obtain the shapes of the experimental spectra. Moreover, taking into account the computational effort associated with this kind of simulation, we develop a method to convert the simulations of energy deposited into light collected, depending only on the interaction point in the detector. This method represents a useful solution when extensive simulations have to be done, as in the case of the calculation of the response function of the spectrometer in a total absorption γ-ray spectroscopy analysis.

The accurate determination of reactor antineutrino spectra remains a very active research topic for which new methods of study have emerged in recent years. Indeed, following the long-recognized reactor anomaly (measured antineutrino deficit in short baseline reactor experiments when compared with spectral predictions), the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have recently demonstrated the existence of spectral distortions in their measurements with respect to the same predictions. These spectral predictions were obtained through the conversion of integral beta-energy spectra obtained at the ILL research reactor. Several studies have shown that the underlying nuclear physics required for the conversion of these spectra into antineutrino spectra is not totally understood. An alternative to such converted spectra is a complementary approach that consists of determining the antineutrino spectrum by means of the measurement and processing of nuclear data. The beta properties of some key fission products suffer from the pandemonium effect which can be circumvented by the use of the Total Absorption Gammaray Spectroscopy technique (TAGS). The two main contributors to the Pressurized Water Reactor antineutrino spectrum in the region where the spectral distortion has been observed are Rb-92 and Cs-142, which have been measured at the radioactive beam facility of the University of Jyvaskyla in two TAGS experiments. We present the results of the analysis of the TAGS measurements of the beta-decay properties of Rb-92 along with preliminary results on Cs-142 and report on the measurements already performed.

The beta decay properties of the T-z = -2, Zn-56 isotope and other proton-rich nuclei in the fp-shell have been investigated in an experiment performed at GANIL. The ions were produced in fragmentation reactions and implanted in a double-sided silicon strip detector surrounded by Ge EXOGAM clovers. Preliminary results for Zn-56 are presented. The Zn-56 decay proceeds mainly by beta delayed proton emission, but beta delayed gamma rays were also detected. Moreover, the exotic beta delayed gamma-proton decay was observed for the first time. The Zn-56 half-life and the energy levels populated in the Cu-56 daughter have been determined. Knowledge of the gamma de-excitation of the mirror states in Co-56 and the comparison with the results of the mirror charge exchange process, the Fe-56(He-3,t) reaction (where Fe-56 has T-z = +2), were important in the interpretation of the Zn-56 decay data. The absolute Fermi and Gamow-Teller strengths have been deduced.

Gamow-Teller (GT) transitions starting from stable as well as unstable pf-shell nuclei are of interest not only in nuclear physics, but also in astrophysics, e.g. in violent neutrino-induced reactions at the core-collapse stage of type II supernovae. In the {beta}-decay study of these pf-shell nuclei, half-lives can be measured rather accurately. On the other hand, in high-resolution ({sup 3}He,t) charge-exchange reactions at 0 deg., individual GT transitions up to high excitations can be studied. Assuming the isospin symmetry for the strengths of T{sub z} = {+-}1{yields}0 analogous GT transitions, we present a unique 'merged analysis' for the determination of absolute B(GT) values. This method can be applied not only to T = 1 systems, but also to higher T systems.

The beta decay of Tc-100 has been studied by using the total absorption gamma-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. In this work the new Decay Total Absorption gamma-ray Spectrometer in coincidence with a cylindrical plastic beta detector has been employed. The beta intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double beta decay of Mo-100.

The beta decay of the N = Z nucleus Kr-72 has been studied with the total absorption spectroscopy technique at ISOLDE (CERN). A total B(GT) = 0.79(4)g(A)(2)/4 pi has been found up to an excitation energy of 2.7 MeV. The B(GT) distribution obtained is compared with predictions from state-of-the-art theoretical calculations to learn about the ground state deformation of Kr-72. Although a dominant oblate deformation is suggested by direct comparison with quasiparticle random phase approximation (QRPA) calculations, beyond-mean-field and shell-model calculations favor a large oblate-prolate mixing in the ground state.

The new Decay Total Absorption Spectrometer (DTAS) has been commissioned with low energy radioactive beams at the upgraded IGISOL IV facility. The DTAS is a segmented detector composed of up to 18 NaI(Tl) crystals and it will be a key instrument in the DESPEC experiment at FAIR. In this document we report on the experimental setup and the first measurements performed with DTAS at IGISOL. The detector was characterized by means of MC simulations, and this allowed us to calculate the response function of the spectrometer and analyse the first cases of interest.

The gamma-decay of excited states in the neutron deficient isotopes Tc-87 and Tc-88 has been observed for the first time. The fusion-evaporation reactions Ni-58(S-32, p2n)Tc-87 and Ni-58(S-32, pn)Tc-88 at 110 MeV, Ca-40(Cr-50, p2n)Tc-87 and Ca-40(Cr-50, pn)Tc-88 at 170 MeV and Ni-58(Ar-36, alpha-pn)Tc-88 at 145 MeV beam energy were used. Unambiguous identification of these nuclei which are populated with less than 1 mb cross section was achieved with coincidences between the gamma-radiation and the evaporation residues detected in a recoil mass separator. From gamma-gamma-coincidence data, a decay scheme of 11 transitions was constructed for Tc-88, the ground state of which is suggested to have I-pi = 7- or 8+. Two transitions identified in Tc-87 follow the pattern of a g9/2 one-quasiparticle band.

In β-decay studies the determination of the decay probability to the ground state (g.s.) of the daughter nucleus often suffers from large systematic errors. The difficulty of the measurement is related to the absence of associated delayed γ-ray emission. In this work we revisit the 4πγ−β method proposed by Greenwood and collaborators in the 1990s, which has the potential to overcome some of the experimental difficulties. Our interest is driven by the need to determine accurately the β-intensity distributions of fission products that contribute significantly to the reactor decay heat and to the antineutrinos emitted by reactors. A number of such decays have large g.s. branches. The method is relevant for nuclear structure studies as well. Pertinent formulas are revised and extended to the special case of β-delayed neutron emitters, and the robustness of the method is demonstrated with synthetic data. We apply it to a number of measured decays that serve as test cases and discuss the features of the method. Finally, we obtain g.s. feeding intensities with reduced uncertainty for four relevant decays that will allow future improvements in antineutrino spectrum and decay heat calculations using the summation method.

Here we present the experimental activities carried out at ISOLDE with the total absorption spectrometer Lucrecia, a large 4 pi scintillator detector designed to absorb a full gamma cascade following beta decay. This spectrometer is designed to measure beta-feeding to excited states without the systematic error called Pandemonium. The set up allows the measurement of decays of very short half life. Experimental results from several campaigns, that focus on the determination of the shapes of beta-decaying nuclei by measuring their beta decay strength distributions as a function of excitation energy in the daughter nucleus, are presented.

The half-lives of the T-Z = -2, Zn-56 and T-Z = -1, Zn-58 isotopes and other nuclei were measured in a beta-decay experiment at GANIL. The energy levels populated by the Zn-56 beta decay were determined. The Zn-56 results are compared with the results of the mirror process, the charge exchange reaction Fe-56(He-3,t)Co-56.

The gamma rays and conversion electrons emitted in the beta decay of Sr-78 to levels in Rb-78 have been studied using Ge detectors and a mini-orange spectrometer. A reliable level scheme based on the results of these experiments has been established. The properties of the levels in Rb-78 have been compared with calculations based on deformed Hartree-Fock with Skyrme interactions and pairing correlations in the BCS approximation. This has allowed an interpretation of the nature of the observed sets of levels in the odd-odd nucleus Rb-78.

Excited states in {sup 86,88}Mo have been identified using recoil-{gamma} and {gamma}{gamma} coincidences. Energy-level systematics of the molybdenum isotopes from the {ital N}={ital Z} line to the {ital N}=50 shell closure are compared to their strontium and zirconium neighbors. This comparison, an estimate of the {ital B}({ital E}2) strengths, and a Woods-Saxon cranking model have been used to suggest that the molybdenum isotopes undergo a transition from spherical to moderately deformed shapes at {sup 86}Mo.

The nuclear structure of neutron-rich N≥126 nuclei have been investigated following their production via relativistic projectile fragmentation of a E/A=l GeV 238U beam on a Be target. The cocktail of secondary beam products were separated and identified using the GSI FRagment Separator (FRS). The nuclei of interest were implanted in a high-granularity active stopper detector set-up consisting of 6 double sided silicon strip detectors. The associated gamma-ray transitions were detected with the RISING array, consisting of 15 Euroball cluster Ge-detectors. Time-correlated gamma decays from individually identified nuclear species have been recorded, allowing the clean identification of isomeric decays.

The M1 admixtures in the 74.6 keV (3 + → 2 +), 122.8 KeV (5 + → 4 +) and 146.3keV (6 + → 5 +) transitions in the γ-vibrational band of 168Er have been determined to be 33 ± 1, 29 ± 2 and 22 ± 6 percent from measurements of L subshell conversion line intensity ratios. It is shown that the M1 admixtures in the intra-band transitions in the γ-band are a general and suprisingly constant feature in deformed rare-earth nuclei. This suggests that they are the result of a collective effect. The theory of Greiner, which takes the diferent deformation of the proton and nuetron cores into account, is found to be able to give a quantitative explanation of the observed M1 admixtures.

In this chapter P-decay is discussed as a tool for studying the structure of atomic nuclei. An attempt is made to give a simple account of the topic so that the student can understand what they find in the literature about beta-decay. The quantities of spectroscopic interest are defined and the student is shown how they can be derived from experiments. In the study of exotic nuclei often the first thing we learn about a nucleus is how it beta-decays. A series of examples of beta-decay studies of exotic nuclei is presented with the aim of both illustrating the most up-to-date techniques and showing the student the breadth of physics that can be addressed

Studying the weak nuclear response, especially the Gamow-Teller (GT) transitions starting from stable as well as unstable nuclei is one of the key issues in nuclear and nuclear-astrophysics. We studied the GT transitions by means of hadronic (He-3, t) charge-exchange reactions and complementary beta decays. Owing to the simple sigma tau nature of the operator that causes GT transitions, information on the crucial and critical part of the nuclear structure can be studied. Under the assumption that isospin is a good quantum number, symmetry is expected for the structure of mirror nuclei and the GT transitions starting from them. The results from beta-decay studies and the strength distribution of GT transitions from the (He-3, t) reaction are compared and also combined for the understanding of nuclear structure of far-from-stability nuclei.

The β decay of ^{208}Hg into the one-proton hole, one neutron-particle _{81}^{208}Tl_{127} nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z

Gamow-Teller (GT) transitions can be studied in both beta- decay and charge exchange(CE) reactions. If isospin is a good quantum number, then the Tz = -1 -> 0 and T-z = +1 -> 0 GT mirror transitions, are identical. Therefore, a comparison of the results from studies of beta decay and CE should shed light on this assumption. Accordingly we have studied the beta decay of the Tz = 1 fp-shell nuclei, Ni-54, Fe-50, Cr-46, and Ti-42, produced in fragmentation and we have compared our results with the spectra from (3 He, t) measurements on the mirror T-x = +1 target nuclei studied in high resolution at RCNP, Osaka. The experiments were performed as part of the STOPPED beam RISING campaign at GSI

Studying the Gamow-Teller (GT) transitions of stable as well as unstable pf-shell nuclei is one of the key issues in nuclear and astro-nuclear physics. Under the assumption that isospin T is a good quantum number, symmetry is expected for mirror nuclei and the GT transitions starting from the mirror nuclei. We study the GT transitions starting from T-z=+/- 1 mirror nuclei, respectively, by means of hadronic (He-3,t) charge-exchange reactions and complementary beta decays

The beta-intensity distributions of the decays of Nb-100gs,Nb-100m and Nb-102gs,Nb-102m have been determined using the total absorption gamma-ray spectroscopy technique. The JYFLTRAP double Penning trap system was employed in a campaign of challenging measurements performed with the decay total absorption gamma-ray spectrometer at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. Different strategies were applied to disentangle the isomeric states involved, lying very close in energy. The low-spin component of each niobium case was populated through the decay of the zirconium parent, which was treated as a contaminant. We have applied a method to extract this contamination, and additionally we have obtained beta-intensity distributions for these zirconium decays. The beta-strength distributions evaluated with these results were compared with calculations in a quasiparticle random-phase approximation, suggesting a prolate configuration for the ground states of Zr-100,Zr-102. The footprint of the Pandemonium effect was found when comparing our results for the analyses of the niobium isotopes with previous decay data. The beta-intensities of the decay of Nb-102m, for which there were no previous data, were obtained. A careful evaluation of the uncertainties was carried out, and the consistency of our results was validated taking advantage of the segmentation of our spectrometer. The final results were used as input in reactor summation calculations. A large impact on antineutrino spectrum calculations was already reported, and here we detail the significant impact on decay heat calculations.

The β decay of 207Hg into the single-proton-hole nucleus 207Tl has been studied through γ-ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the πs−11/2, πd−13/2, and πh−111/2 shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s1/2-coupled) are identified and three more states (d3/2-coupled) are tentatively assigned using spin-parity inferences, while further h11/2-coupled states may also have been observed for the first time. Comparisons are made with state-of-the-art large-scale shell model calculations and previous observations made in this region, and systematic underestimation of the energy of the octupole vibrational states is noted. We suggest that in order to resolve the difference in predicted energies for collective and noncollective t=1 states (t is the number of nucleons breaking the 208Pb core), the effect of t=2 mixing may be reduced for octupole-coupled states. The inclusion of mixing with t=0,2,3 excitations is necessary to replicate all t=1 state energies accurately.

The beta-delayed neutron emission probability, P-n, of very exotic nuclei is crucial for the understanding of nuclear structure properties of many isotopes and astrophysical processes such as the rapid neutron capture process (r-process). In addition beta-delayed neutrons are important in a nuclear power reactor operated in a prompt sub-critical, delayed critical condition, as they contribute to the decay heat inducing fission reactions after a shut down. The study of neutron-rich isotopes and the measurement of beta-delayed one-neutron emitters (beta 1n) is possible thanks to the Rare Isotope Beam (RIB) facilities, where radioactive beams allow the production of exotic nuclei of interest, which can be studied and analyzed using specific detection systems. This contribution reports two recent measurements of beta-delayed neutron emitters which allowed the determination of half-lives and the neutron branching ratio of isotopes in the mass region above A = 200 and N > 126, and a second experiment which confirmed Sb-136 as the heaviest double neutron emitter (beta 2n) measured so far.

We report the observation of a very exotic decay mode at the proton drip line, the beta-delayed gamma-proton decay, clearly seen in the beta decay of the T-z = -2 nucleus Zn-56. Three gamma-proton sequences have been observed after the beta decay. Here this decay mode, already observed in the sd shell, is seen for the first time in the f p shell. Both. and proton decays have been taken into account in the estimation of the Fermi and Gamow-Teller strengths. Evidence for fragmentation of the Fermi strength due to strong isospin mixing is found.

The beta decays of the proton-rich, T-z = -2 nuclei Fe-48, Ni-52 and Zn-56 were investigated by decay spectroscopy at GANIL. The decay schemes were determined, together with absolute Fermi and Gamow-Teller transition strengths. New interesting results were obtained, including the first observation of a new decay mode in the fp-shell, the exotic beta-delayed gamma-proton decay seen in Zn-56, and the first observation of the 2(+) isomer in Co-52. These studies were complemented by Charge Exchange reactions on the stable mirror targets.

A study of the beta decay of the proton-rich T-z = 2 nucleus Zn-56 has been reported in a recent publication. A rare and exotic decay mode, beta-delayed gamma-proton decay, has been observed there for the first time in the fp shell. Here, we expand on some of the details of the data analysis, focussing on the charged particle spectrum.

In this work we report on total absorption gamma-ray spectroscopy measurements of the ss decay of fission products that are important contributors to the antineutrino spectrum. The experiment was performed at IGISOL as a part of a campaign of measurements with the new DTAS spectrometer. Preliminary results of the analysis of the ss decay of Nb-100, Nb-100m and Cs-140 are presented.

Excited states in the very neutron deficient isotope Nb83 were observed for the first time in the reaction Si-28(Ni-58,2np)Nb83 at 195 MeV. Identification was made with a recoil separator and a cross section of sigma = 180(80) mu-b was estimated. Eight transitions were arranged in a level scheme which resembles the N = 41 isotones Kr77 and Sr79 rather than the heavier, weakly deformed Nb isotopes. This suggests that a shape transition to strong deformation exists in the light Nb isotopes. A ground state spin of 5/2+ is suggested.

The decay heat of the fission products plays an important role in predicting the heat-up of nuclear fuel after reactor shutdown. This form of energy release is calculated as the sum of the energy-weighted activities of all fission products P(t) = {sigma}E{sub i}{lambda}{sub i}N{sub i}(t), where E{sub i} is the decay energy of nuclide i(gamma and beta component), {lambda}{sub i} is the decay constant of nuclide i and N{sub i}(t) is the number of nuclide i at cooling time t. Even though the reproduction of the measured decay heat has improved in recent years, there is still a long standing discrepancy at t{approx}1000 s cooling time for some fuels. A possible explanation for this disagreement can been found in the work of Yoshida et al., who demonstrated that an incomplete knowledge of the {beta}-decay of some Tc isotopes could be the source of the systematic discrepancy. We have recently measured the {beta}-decay process of some Tc isotopes using a total absorption spectrometer at the IGISOL facility in Jyvaeskylae. The results of the measurements are discussed, along with their impact on summation calculations.

Total Absorption Spectroscopy measurements of the beta decay of Mo-103 and Tc-103, important contributors to the decay heat summation calculation in reactors, are reported in this work. The analysis of the experiment, performed at IGISOL with the new DTAS detector, show new beta intensity that was not detected in previous measurements with Ge detectors.

A 20/30 MV Tandem Van de Graaff machine is about to begin regular operation at Daresbury in Cheshire. Some of the associated experimental facilities are described, with particular emphasis on those intended for the study of nuclei far from stability. Both a recoil separator and a mass separator are under construction, and their characteristics are discussed. Alternative, cheaper methods of studying nuclei far from stability are described. The results of some experiments, which make use of these techniques, on nuclei with Z ∼ N ∼ 40, neutron-deficient Sn nuclei and neutron-deficient Yb nuclei are also discussed.

Due to the simplicity of the or operator that causes Gamow-Teller (GT) transitions, they are the most popular nuclear weak process in the Universe. The GT transitions in pf-shell nuclei, for example, starting from stable T-z = +1 and proton-rich T-z = -1 nuclei, where T-z = (N-Z)/2, play important roles in the supernova-explosion or rp-process nucleosynthesis. In the beta-decay study of pf-shell nuclei, half-lives can be measured rather accurately. On the other hand, in a high-resolution (He-3, t) charge-exchange reaction at 0 degrees, individual GT transitions up to high excitations can be studied. In order to derive reliable GT transition strengths B(GT), we present a unique analysis that combines the strength distribution form the (He-3,t) measurement with the information from the study of mirror beta decay, where good isospin symmetry of T-z = +/- 1 -> 0 transitions is assumed.

Preliminary results from beta decay studies of nuclei that are important for reactor applications are presented. The beta decays have been studied using the total absorption technique (TAS) and the pure beams provided by the JYFLTRAP system at the IGISOL facility of the University of Jyvaskyla.

The beta feeding probability of Tc-102,Tc- 104,Tc- 105,Tc- 106,Tc- 107, Mo-105, and Nb-101 nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the gamma component of the decay heat for Pu-239 in the 4-3000 s range.

The beta-feeding probabilities for three important contributors to the decay heat in nuclear reactors, namely Tc-102,Tc-104,Tc-105, have been measured using the total absorption spectroscopy technique. For the measurements, sources of very high isobaric purity have been obtained using a Penning trap (JYFLTRAP). A detailed description of the data analysis is given and the results are compared with high-resolution measurements and theoretical calculations. DOI: 10.1103/PhysRevC.87.044318

The contribution of each fission fragment to the reactor antineutrino spectra was determined using the summation method based on the existing information on fission yields and decay data contained in nuclear databases and the reactor evolution code MURE. The beta decay of some of the main contributors has been studied using the Total Absorption Spectroscopy (TAS) technique during two experimental campaigns at the IGISOL facility, in Jyväskylä (Finland). Results on the decay of 92Rb, the most important contributor in the 4–8 MeV energy region are reported. The status of the analysis of the second experiment is presented as well.

The decay heat of fission products plays an important role in predictions of the heat up of nuclear fuel in reactors. The released energy is calculated as the summation of the activities of all fission products P(t) = Sigma E-i lambda(i) N-i(t), where E-i is the decay energy of nuclide i (gamma and beta component), lambda(i) is the decay constant of nuclide i and N-i(t) is the number of nuclide i at cooling time t. Even though the reproduction of the measured decay heat has improved in recent years, there is still a long standing discrepancy in the t similar to 1000 s cooling time for some fuels. A possible explanation to this improper description has been found in the work of Yoshida et al. [1], where it has been shown that the incomplete knowledge of the, beta-decay of some Tc isotopes can be the source of the systematic discrepancy. Motivated by [1], we have recently measured the beta-decay process of some Tc isotopes using a total absorption spectrometer at the IGISOL facility in Jyvaskyla. The results of the measurements as well as the their consequences on summation calculations are discussed.

The decay heat of fission products plays an important role in predictions of the heat up of nuclear fuel in reactors. The released energy is calculated as the summation of the activities of all fission products P(t) = Sigma E-i lambda N-i(i)(t), where E-i is the decay energy of nuclide i,lambda(i) is the decay constant of nuclide i and N-i(t) is the number of nuclide i at cooling time t. Even though the reproduction of the measured decay heat has improved in recent years, there is still a long standing discrepancy in the t similar to 1000s cooling time for some fuels. A possible explanation to this improper description has been found in the work of Yoshida et al [1], where it has been shown that the incomplete knowledge of the beta-decay of some Tc isotopes can be the source of the systematic discrepancy. Motivated by [1], we have recently measured the beta-decay process of some Tc isotopes using a total absorption spectrometer at the IGISOL facility in Jyvaskyla. The results of the measurements as well as the their consequences on summation calculations are discussed.

The highest spin states in a T(z)=1/2 nucleus have been observed in 77Sr: I(pi)=(49/2+) and (29/2-). In addition, states up to I(pi)=(22+) have been seen in 78Sr. The alpha=1/2, g9/2 band and both signature partners of the negative parity band in 77Sr were found to be identical to the yrast band in 78Sr with relative alignments of 1.22(7)HBAR, 0.52(5)HBAR (alpha=1/2), and 0.42(4)HBAR (alpha=-1/2), respectively. In one of the negative parity bands, the identicality persists through the first proton band crossing. The odd spin decay sequence of the 4- band in 78Rb is identical to the ground band of 78Sr [3.02(3)HBAR] at low spin and to the alpha=1/2, g9/2 band in 77Rb [1.11(3)HBAR] at higher spins. These are the only known examples of identical bands in the neutron deficient A=80 region. The analysis indicates that the [301]3/2 Nilsson orbital is a very good spectator orbital.

A total absorption spectrometer, dedicated to the study of very short lived atomic species, has been built and installed at the CERN/ISOLDE mass separator. The beta decays of the neutron-deficient Kr-74 and Sr-76 nuclei have been studied using this new device. The experimental Gamow-Teller strength distributions obtained over the full Q(EC) windows are presented and compared with self-consistent, deformed, HF-BCS-QRPA calculations.

A complete characterisation of the β-decay of neutron-rich nuclei can be obtained from the measurement of β-delayed gamma rays and, whenever the process is energetically possible, β-delayed neutrons. The accurate determination of the β-intensity distribution and the β-delayed neutron emission probability is of great relevance in the fields of reactor technology and nuclear astrophysics. A programme for combined measurements using the total absorption gamma-ray spectroscopy technique and both neutron counters and neutron time-of-flight spectrometers is presented.

A new summation method model of the reactor antineutrino energy spectrum is presented. It is updated with the most recent evaluated decay databases and with our total absorption gamma-ray spectroscopy measurements performed during the last decade. For the first time, the spectral measurements from the Daya Bay experiment are compared with the antineutrino energy spectrum computed with the updated summation method without any renormalization. The results exhibit a better agreement than is obtained with the Huber-Mueller model in the 2–5 MeV range, the region that dominates the detected flux. A systematic trend is found in which the antineutrino flux computed with the summation model decreases with the inclusion of more pandemonium-free data. The calculated flux obtained now lies only 1.9% above that detected in the Daya Bay experiment, a value that may be reduced with forthcoming new pandemonium-free data, leaving less room for a reactor anomaly. Eventually, the new predictions of individual antineutrino spectra for the U235, Pu239, Pu241, and U238 are used to compute the dependence of the reactor antineutrino spectral shape on the fission fractions.

The beta decay of the odd-odd nucleus Br-70 has been investigated with the BigRIPS and EURICA setups at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center. The T = 0(J(pi) = 9(+)) and T = 1(J(pi) = 0(+)) isomers have both been produced in in-flight fragmentation of Kr-78 with ratios of 41.6(8)% and 58.4(8)%, respectively. A half-life of t(1/2) = 2157(-49)(+53) ms has been measured for the J pi = 9(+) isomer from gamma-ray time decay analysis. Based on this result, we provide a new value of the half-life for the J pi = 0(+) ground state of Br-70, t(1/2) = 78.42 +/- 0.51 ms, which is slightly more precise, and in excellent agreement, with the best measurement reported hitherto in the literature. For this decay, we provide the first estimate of the total branching fraction decaying through the 2(1)(+) state in the daughter nucleus Se-70, R(2(1)(+)) = 1.3 +/- 1.1%. We also report four new low-intensity gamma-ray transitions at 661, 1103, 1561, and 1749 keV following the beta decay of the J pi = 9(+) isomer. Based on their coincidence relationships, we tentatively propose two new excited states at 3945 and 4752 keV in 70Se with most probable spins and parities of J(pi) = (6(+)) and (8(+)), respectively. The observed structure is interpreted with the help of shell-model calculations, which predict a complex interplay between oblate and prolate configurations at low excitation energies.

We have performed new accurate measurements of the beta-delayed neutron emission probability for ten isotopes of the elements Y, Sb, Te and I. These are fission products that either have a significant contribution to the fraction of delayed neutrons in reactors or are relatively close to the path of the astrophysical r process. The measurements were performed with isotopically pure radioactive beams using a constant and high efficiency neutron counter and a low noise beta detector. Preliminary results are presented for six of the isotopes and compared with previous measurements and theoretical calculations.

James Philip Elliott made important contributions to improve our understanding of the structure of atomic nuclei in the second half of the twentieth century. In 1958 he proposed the SU(3) model, explaining rotational behaviour of nuclei in the context of the shell model. His idea, based on elegant and seminal group-theoretical concepts, reconciled the independent-particle with the liquid-drop model, which until then existed as disconnected views of the nucleus. In the 1960s and 1970s he developed methods to extract properties of the nuclear interaction from the phase shifts of nucleon–nucleon scattering. From 1980 until his death he contributed to the development of the interacting boson model of Arima and Iachello, and its microscopic understanding in terms of symmetries of the shell model. For his outstanding achievements in theoretical physics, in 2002 he and Francesco Iachello were awarded the Lise Meitner prize of the European Physical Society for ‘their innovative applications of group-theoretical methods to the understanding of atomic nuclei’. His achievements were also recognized by the award of the Rutherford Medal and Prize of the Institute of Physics in 1994.

Beta-decay experiments are a primary source of,information for nuclear-structure studies and at the same time complementary to in-beam investigations of nuclei far from stability. Although both types of experiment are mainly based on gamma-ray spectroscopy, they face different experimental problems. The so-called Pandemonium effect is a critical problem in beta-decay if we are to test theoretically calculated transition probabilities. In this contribution we will present a solution to this problem using total absorption spectroscopy methods. We will also present some examples of experiments carried out with the Total Absorption Spectrometer (TAS) at GSI an describe a new device LUCRECIA recently installed at CERN.

Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of gamma emission from neutron-unbound states populated in the beta-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission one can deduce information on the (n,gamma) cross section for unstable neutron-rich nuclei of interest in r process abundance calculations. A surprisingly large gamma branching was observed for a number of isotopes. The results are compared with Hauser-Feshbach calculations and discussed.

The average spins at which final fragments are formed after fission following fusion of 19F with 197Au have been measured directly from spectroscopic studies of discrete γ-ray lines. The final fragment spins can be translated into average spins at which primary fragments are formed by adding changes due to statistical γ-ray emission and post-fission neutron emission. The average primary fragment spins show marked variations with fragment mass. Possible causes for the structure are discussed within the framework of the statistical scission model of heavy-ion induced fission.

We have measured the beta-decay half-lives of 16 neutron-deficient nuclei with T-z = -1/2 and -1, ranging from chromium to germanium. They were produced in an experiment carried out at GANIL and optimized for the production of Zn-58, for which in addition we present the decay scheme and absolute Fermi and Gamow-Teller transition strengths. Since all of these nuclei lie on the rp-process pathway, the T-1/2 values are important ingredients for the rp-process reaction flow calculations and for models of X-ray bursters.

The effect of beam intensity and beam pulse repetition rate on the transport efficiency of 104Ag recoils [from the 103Rh(α, 3n) reaction] in a He jet recoil transport system has been measured. Transport was effected by using the gas doped with benzene or diethyl sulphide. The effect of concentration for these two substances has been established and the maximum transport efficiencies were about 100% for benzene (22 ppm) and about 80% for diethyl sulphide (12 ppm).

Gamow-Teller (GT) transitions can be studied in both beta decay and charge exchange (CE) reactions. If isospin is a good quantum number, then the T-z = -1 -> 0 and Tz = + 1 -> 0 GT mirror transitions, are identical. Therefore, a comparison of the results from studies of beta decay and CE should shed light on this assumption. Accordingly we have studied the beta decay of the Tz = -1 fp-shell nuclei, Ni-54, Fe-50, Cr-46, and Ti-42, produced in fragmentation and we have compared our results with the spectra from (He-3, t) measurements on the mirror Tz = +1 target nuclei studied in high resolution at RCNP, Osaka. The beta decay experiments were performed as part of the STOPPED beam RISING campaign at GSI.

This conference paper outlines the operation and some of the preliminary physics results using the GSI RISING active stopper. Data are presented from an experiment using combined isomer and beta-delayed gamma-ray spectroscopy to study low-lying spectral and decay properties of heavy-neutron-rich nuclei around A similar to 90 produced following the relativistic projectile fragmentation of Pb-208 primary beam. The response of the RISING active stopper detector is demonstrated for both the implantation of heavy secondary fragments and in-situ decay of beta-particles. Beta-delayed gamma-ray spectroscopy following decays of the neutron-rich nucleus Re-194 is presented to demonstrate the experimental performance of the set-up. The resulting information inferred from excited states in the W and Os daughter nuclei is compared with results from Skyrme Hartree-Fock predictions of the evolution of nuclear shape.

DTAS is a segmented total absorption γ-ray spectrometer developed for the DESPEC experiment at FAIR. It is composed of up to eighteen NaI(Tl) crystals. In this work we study the performance of this detector with laboratory sources and also under real experimental conditions. We present a procedure to reconstruct offline the sum of the energy deposited in all the crystals of the spectrometer, which is complicated by the effect of NaI(Tl) light-yield non-proportionality. The use of a system to correct for time variations of the gain in individual detector modules, based on a light pulse generator, is demonstrated. We describe also an event-based method to evaluate the summing-pileup electronic distortion in segmented spectrometers. All of this allows a careful characterization of the detector with Monte Carlo simulations that is needed to calculate the response function for the analysis of total absorption γ-ray spectroscopy data. Special attention was paid to the interaction of neutrons with the spectrometer, since they are a source of contamination in studies of β-delayed neutron emitting nuclei.

Preliminary results of an experimental study of the beta-decay of the exotic T-z = -2, Zn-56 nucleus and other proton-rich T-z = 1 nuclei are presented. The ions were produced at GANIL using fragmentation reactions, separated by the LISE3 spectrometer and implanted in a double-sided silicon strip detector surrounded by Ge detectors. The half-lives of Zn-56 and four T-z= - 1 nuclei in the fp-shell have been measured. While the decay of the Tz = 1 nuclei proceeds essentially by beta-delayed gamma emission, in the case of 56Zn beta-delayed proton emission is also observed. Moreover, the exotic beta-delayed gamma-proton decay is seen for the first time. The information from the decay study has been used to determine the absolute Fermi and Gamow Teller transition strengths. The results for Zn-56 have been compared with the mirror Charge Exchange process, the (He-3,t) reaction on the Tz = +2, Fe-56 target nucleus. This comparison is important for understanding the Zn-56 decay data.

The gamma ray decays of excited states in the nuclei 128,130,132Nd have been identified as the result of measurements of multiple particle-gamma coincidences. The reactions 40Ca + 92Mo and 40Ca + 96Ru were studied at bombarding energies ranging from 147 to 200 MeV. Gamma-ray excitation functions were measured over this energy range. In the case of the 92Mo( 40Ca, 2p) 130Nd reaction, the angular distributions of the emitted gamma rays were also measured at 180 MeV bombarding energy. The lifetimes of the lowest states in the ground-state bands of these nuclei were measured using the recoil distance method. The results are consistent with these nuclei possessing large, permanent, ground state deformations with typical values of ε 2 ≈ 0.3. The ground state rotational bands of all the nuclei studied exhibit band crossings at h ̵ ω c ≈0.32 MeV . This appears to be due to the alignment of h 11 2 protons. The results are discussed in the light of recent potential energy surface and cranked-shell-model calculations.

The possibility that high-spin isomers in heavy nuclei might undergo fission has been investigated experimentally. The partial fission lifetime of the 34 mu s, I = 34 isomer in Fr-212 is found to be at least one hour.

During the last decade we have carried out a systematic study of the β decay of neutron-deficient nuclei, providing rich spectroscopic information of importance for both nuclear structure and nuclear astrophysics. We present an overview of the most relevant achievements, including the discovery of a new exotic decay mode in the fp-shell, the β-delayed γ-proton decay in 56Zn, the first observation of the 2+ isomer in 52Co and the latest results on the heavier systems 60Ge and 62Ge. We also report on our deduced mass excesses in comparison with systematics and a recent measurement. Finally, we summarise our results on the half-lives of Tz = -1/2, -1 and -2 neutron-deficient nuclides, and analyse their trend.

The shape of the spectrum corresponding to the electrons emitted in $\beta$ decay carries a wealth of information about nuclear structure and fundamental physics. In spite of that, few dedicated measurements have been made of β-spectrum shapes. In this work we present a newly developed detector for β electrons based on a telescope concept. A thick plastic scintillator is employed in coincidence with a thin silicon detector. First measurements employing this detector have been carried out with mono-energetic electrons from the high-energy resolution electron-beam spectrometer at Bordeaux. Here we report on the good reproduction of the experimental spectra of mono-energetic electrons using Monte Carlo simulations. This is a crucial step for future experiments, where a detailed Monte Carlo characterization of the detector is needed to determine the shape of the $\beta$-electron spectra by deconvolution of the measured spectra with the response function of the detector. A chamber to contain two telescope assemblies has been designed for future β-decay experiments at the Ion Guide Isotope Separator On-Line facility in Jyväskylä, aimed at improving our understanding of reactor antineutrino spectra.

The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb and Bi in the mass region N&126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints to global theoretical models currently used in r-process nucleosynthesis.

A multinucleon transfer reaction between a thin self-supporting Pt-198(78) target and an 850 MeV Xe-136(54) beam has been used to populate and study the structure of the N=80 isotone Ba-136(56). Making use of time-correlated gamma-ray spectroscopy, evidence for an I-pi=(10(+)) isomeric state has been found with a measured half-life of 91+/-2 ns. Prompt-delayed correlations have also enabled the tentative, measurement of the near-yrast states which lie above the isomer. Shell-model calculations suggest that the isomer has a structure which can be assigned predominantly as (nuh(11/2))(10+)(-2). The results are discussed in terms of standard and pair-truncated shell-model calculations, and compared to the even-Z N=80 isotones ranging from Sn-130(50) to Er-148(68). A qualitative explanation of the observed dramatic decrease in the B(E2:10(+)-->8(+)) value for the N=80 isotones at Ba-136 is given in terms of the increasing single-hole energy of the h(11/2) neutron configuration as the proton subshell is filled. The angular momentum transfer to the binary fragments in the reaction has also been investigated in terms of the average total gamma-ray fold versus the scattering angle of the recoils.

A novel method of deducing the deformation of the N=Z nucleus Sr-76 is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of quasi-random-phase approximation calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large total absorption gamma spectrometer, "Lucrecia," newly installed at CERN-ISOLDE.

The accurate determination of reactor antineutrino spectra is still a challenge. In 2017 the Daya Bay experiment has measured the evolution of the antineutrino flux with the fuel content of the reactor core. The observed deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of U-235 while the part dominated by the fission of Pu-239 was in good agreement with the conversion model. The TAGS collaboration has carried out two experimental campaigns during the last decade at the JYFLTRAP of Jyvaskyla (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. These measurements allow the correction of the nuclear data for the Pandemonium effect, thus making an important contribution to calculating the antineutrino spectra. The impact of these ten years of measurement from our collaboration on the predicted antineutrino energy spectrum and flux are shown using our summation calculations. The results are compared with the Daya Bay measurements showing the best agreement in shape (in the antineutrino energy range 2 to 5 MeV) and in flux obtained so far with a model. The flux deficit observed by Daya Bay with respect to the summation method is now reduced to 1.9% leaving little room for the reactor anomaly. The shape anomaly between 5 and 7 MeV in antineutrino energy is still observed and remains unexplained.

Beta-decay of the very neutron-deficient Kr isotope, Kr-70, was studied at RIKEN-RIBF using the EURICA cluster array. The experiment significantly increased our knowledge of the beta-decay of this isotope. Namely, 16 new gamma-ray transitions were identified and the half-life was derived from time correlations of the beta particles (t(1/2)(i beta) = (44.99 +/- 0.16) ms) and from the decay curves of the observed gamma-ray transitions (t(1/2)(i beta gamma) = (45.16 +/- 0.71) ms), respectively.

The nuclear structure of neutron-rich N > 126 nuclei has been investigated following their production via relativistic projectile fragmentation of a E/A = 1 GeV (238)U beam on a Be target. The preliminary analysis indicates the presence of previously unreported isomeric states in the N = 128 isotones (208)Hg and (209)Tl.

In this contribution we summarize the recent study of the beta decay of neutron-rich nuclei with isomeric states close in energy to the ground states. The disentanglement of each pair of beta-decaying states was achieved by applying different strategies and using the purification capabilities of the JYFLTRAP double Penning trap system at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. The Total Absorption gamma-ray Spectroscopy technique was employed to determine the beta intensity probabilities populating the excited states in the daughter nuclei. Previously undetected beta intensity was found and we have already evaluated the impact of part of these results on reactor summation calculations. The possibility to populate states associated with the Pygmy Dipole Resonance in the beta decay of Y-96gs has also been investigated thanks to the sensitivity of our technique to high-lying strength in the daughter nuclei.

We report on the preliminary results from a study of the decay of the I-pi = 8(+) T-1/2 = 2 mu s isomer in Pd-96 performed as part of the Stopped-Beam RISING campaign within the Rare Isotope Investigation at GSI (RISING). The Pd-96 ions were produced following the projectile fragmentation of a 750 MeV per nucleon Ag-107 primary beam. The reaction products were separated and identified by the in-flight method using the GSI Fragment Separator. The residues of interest were stopped in a perspex stopper surrounded by an array of 15, seven-element germanium Cluster detectors. One of the goals of the current work is to investigate the population of high-spin states produced projectile fragmentation reactions using isomeric ratio measurements to infer information on the angular momentum population distribution. In this short contribution the method and results of determining the isomeric ratio for the I-pi = 8(+) microsecond isomer in Pd-96 nucleus are presented.

The beta decays of 86Br and 91Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the IGISOL facility in Jyvaskyla and further purified using the JYFLTRAP. 86Br and 91Rb are considered high priority contributors to the decay heat in reactors. In addition 91Rb was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam et al. assuming that this decay was well known from high-resolution measurements. Our results shows that both decays were suffering from the Pandemonium effect and that the results of Rudstam et al. should be renormalized.

β-decay properties of fission products are very important for applied reactor physics, for instance to estimate the decay heat released immediately after the reactor shutdown and to estimate the ν flux emitted. An accurate estimation of the decay heat and the ν emitted flux from reactors, are necessary for purposes such as reactors operation safety and non-proliferation. In order to improve the precision in the prediction for these quantities, the bias due to the Pandemonium effect affecting some important fission product data has to be corrected. New measurements of fission products β-decay, not sensitive to this effect, have been performed with a Total Absorption Spectrometer (TAS) at the JYFL facility of Jyväskylä. An overview of the TAS technique and first results from the 2009 campaign will be presented. © Owned by the authors, published by EDP Sciences, 2014.

Fragmentation products from a 92Mo beam on a natural nickel target have been used to study structural properties of the very neutron deficient nuclei around N∼Z∼40. We present the first observation of isomeric decays in the Tz=1 systems 3674Kr, 3980 Y and 4184Nb. The isomer in 74Kr is interpreted as the hindered decay from an excited 0+ state, confirming the prediction of prolate/oblate shape coexistence in this nucleus. Transitions from states below an isomer in the N=Z nucleus 4386Tc have also been tentatively identified, making this the heaviest N=Z system for which decays from excited states have been observed. In addition, we have obtained the first conclusive evidence for the existence of the Tz = -1/2 isotopes 3977Y, 4079Zr and 4283Mo. The data for 3977Y is of particular interest in light of the reported instability in the lighter odd-Z, Tz = -1/2 systems 69Br and 73Rb.

The half-life of the yrast I π = 2+ state in the neutron-rich nucleus 188W has been measured using fast-timing techniques with the HPGe and LaBr3:Ce array at the National Institute of Physics and Nuclear Engineering, Bucharest. The resulting value of t1/2 = 0.87(12) ns is equivalent to a reduced transition probability of B(E2; 2+ 1 → 0+ 1 ) = 85(12) W.u. for this transition. The B(E2; 2+ 1 → 0+ 1 ) is compared to neighboring tungsten isotopes and nuclei in the Hf, Os, and Pt isotopic chains. Woods-Saxon potential energy surface (PES) calculations have been performed for nuclei in the tungsten isotopic chain and predict prolate deformed minima with rapidly increasing γ softness for 184–192W and an oblate minimum for 194W.

The Gamow-Teller strength distribution of the decay of Hg-186 into Au-186 has been determined for the first time using the total absorption gamma spectroscopy technique and has been compared with theoretical QRPA calculations using the SLy4 Skyrme force. The measured Gamow-Teller strength distribution and the half-life are described by mixing oblate and prolate configurations independently in the parent and daughter nuclei. In this theoretical framework the best description of the experimental beta strength is obtained with dominantly prolate components for both parent Hg-186 and daughter Au-186. The approach also allowed us to determine an upper limit of the oblate component in the parent state. The complexity of the analysis required the development of a new approach in the analysis of the X-ray gated total absorption spectrum. (C) 2021 The Authors. Published by Elsevier B.V.

Nuclear beta decay provides a sensitive and rich tool for studying the structure of atomic nuclei as well as assessing the limits of our understanding of the weak interaction. In this chapter the history of the topic is presented. The main quantities associated with beta-decay spectroscopy are defined. Nuclear structure studies are illustrated by some selected examples of the beta decay of exotic nuclei, also aimed at presenting the most up-to-date techniques. The examples include the decay of 52Ni, 100Sn, and 132Sn and a discussion about the islands of inversion. The studies of the structure of the weak interaction and the tests of fundamental symmetries are illustrated through the most precise measurement of spectroscopic quantities and correlation terms, which have the largest impact on searches for new physics beyond the standard electroweak model. These measurements are motivated by the extraction of the strength of the weak interaction, the search for exotic couplings, and tests of parity and time-reversal symmetries.

The quenching of the experimental spectroscopic factor for the proton decay of 151mLu from the short-lived d3=2 isomeric state has been a long standing problem. In the present work, the proton energy value and half-life of this isomer were remeasured to be 1295(5) keV and 15.4 0.8 s, respectively, in an experiment at the Accelerator Laboratory of the University of Jyvaskyla. The re ned experimental data can resolve the discrepancy in the spectroscopic factor with the WKB approximation. It is also found that the proton formation probability extracted from the present measurements is much larger than that from the adopted data before, indicating no signi cant hindrance for the proton decay of 151mLu.

We report here on the first results obtained from the study of the 24Ne(d, p)25Ne reaction performed with SPIRAL beam at GANIL using the new TIARA+V AMOS+EXOGAM setup. © 2007.

The positive-parity yrast states in the 89Rb, 92Y, and 93Y nuclei were studied using gamma-ray spectroscopy with heavy-ion induced reactions. In the multinucleon transfer reactions 208Pb+90Zr (590 MeV) and 238U+82Se (505 MeV), several gamma-ray transitions were identified in these nuclei by means of coincidences between recoiling ions identified with the PRISMA spectrometer and gamma rays detected with the CLARA gamma-ray array in thin target experiments. Level schemes were subsequently determined from triple gamma coincidences recorded with the GASP array in a thick target experiment, in the reactions produced by a 470 MeV 82Se beam with a 192Os target. The observed level schemes are compared to shell-model calculations.

The very neutron deficient Z = N + 1 nuelei 7739Y, 7940Zr, and 8342Mo have been observed for the first time following the fragmentation of a 92Mo beam. In contrast, no evidence was found for the existence of 8141Nb and 8543Tc. The observation of 7739Y is of particular interest in light of the instability of the odd-proton, Z = N + 1 systems, 6935Br, 7337Rb, 8141Nb, and 8543Tc, and may be explained as a consequence of the shape polarizing effect of the highly deformed, prolate Z = N = 38 core. The experimental results are discussed within the framework of the shell-correction model, which together with proton-decay calculations allow an estimate of the proton separation energies of these highly exotic systems to be calculated.

Gamma decays from excited states up to J(pi)=6() in the N=Z-2 nucleus Ni-54 have been identified for the first time. Level energies are compared with those of the isobars Co-54 and Fe-54 and of the cross-conjugate nuclei of mass A=42. The good but puzzling f(7/2) cross-conjugate symmetry in mirror and triplet energy differences is analyzed. Shell model calculations reproduce the new data but the necessary nuclear charge-dependent phenomenology is not fully explained by modern nucleon-nucleon potentials.

The beta decays of 86Br and 91Rb have been studied using the total absorption spectroscopy technique. The radioactive nuclei were produced at the Ion Guide Isotope Separator On-Line facility in Jyväskylä and further purified using the JYFLTRAP. 86Br and 91Rb are considered to be major contributors to the decay heat in reactors. In addition, 91Rb was used as a normalization point in direct measurements of mean gamma energies released in the beta decay of fission products by Rudstam et al. assuming that this decay was well known from high-resolution measurements. Our results show that both decays were suffering from the Pandemonium effect and that the results of Rudstam et al. should be renormalized. The relative impact of the studied decays in the prediction of the decay heat and antineutrino spectrum from reactors has been evaluated

In order to determine the Gamow‐Teller strength distribution for the N  =  Z nucleus 72Kr an experiment was performed with a Total Absorption Gamma Spectrometer. To fully accomplish this task it is crucial to determine the multipolarity of the low energy transitions as the spin‐parity of the daughter ground state has been debated. This is done by experimental determination of the conversion coefficients. Preliminary results for the multipolarity and conversion coefficients of the transition connecting the isomeric state at 101 keV with the 72Br ground state are presented.

The positive-parity yrast states in the Rb-89, Y-92, and Y-93 nuclei were studied using gamma-ray spectroscopy with heavy-ion induced reactions. In the multinucleon transfer reactions Pb-208+Zr-90 (590 MeV) and U-238+Se-82 (505 MeV), several gamma-ray transitions were identified in these nuclei by means of coincidences between recoiling ions identified with the PRISMA spectrometer and gamma rays detected with the CLARA gamma-ray array in thin target experiments. Level schemes were subsequently determined from triple-gamma coincidences recorded with the GASP array in a thick target experiment, in the reactions produced by a 470 MeV Se-82 beam with a Os-192 target. The observed level schemes are compared to shell-model calculations.

In this review we will present the results of recent $\beta $-decay studies using the total absorption technique that cover topics of interest for applications, nuclear structure and astrophysics. The decays studied were selected primarily because they have a large impact on the prediction of (a) the decay heat in reactors, important for the safety of present and future reactors and (b) the reactor electron anti-neutrino spectrum, of interest for particle/nuclear physics and reactor monitoring. For these studies the total absorption technique was chosen, since it is the only method that allows one to obtain $\beta $-decay probabilities free from a systematic error called the Pandemonium effect. The total absorption technique is based on the detection of the $\gamma $ cascades that follow the initial $\beta $ decay. For this reason the technique requires the use of calorimeters with very high $\gamma $ detection efficiency. The measurements presented and discussed here were performed mainly at the IGISOL facility of the University of Jyväskylä (Finland) using isotopically pure beams provided by the JYFLTRAP Penning trap. Examples are presented to show that the results of our measurements on selected nuclei have had a large impact on predictions of both the decay heat and the anti-neutrino spectrum from reactors. Some of the cases involve $\beta $-delayed neutron emission thus one can study the competition between $\gamma $- and neutron-emission from states above the neutron separation energy. The $\gamma $-to-neutron emission ratios can be used to constrain neutron capture (n,$\gamma $) cross sections for unstable nuclei of interest in astrophysics. The information obtained from the measurements can also be used to test nuclear model predictions of half-lives and Pn values for decays of interest in astrophysical network calculations. These comparisons also provide insights into aspects of nuclear structure in particular regions of the nuclear chart.

A systematic study of the beta-decay of neutron-deficient nuclei has been carried out and has provided spectroscopic information of importance for both nuclear structure and nuclear astrophysics. Following an overview of the most relevant achievements, we focus on the latest results on the beta decay of Ge-60 and Ge-62. We also summarise our results on the mass excesses in comparison with systematics and a recent measurement. Finally, we present updated halflife trends for T-z = -1/2, -1 and -2 neutron-deficient nuclides.

Nuclear reactors antineutrino measurements at short baselines do not fully agree with model predictions calculated with the Conversion Method. An alternative method to calculate the antineutrino spectra is the Summation Method. Both methods require the shapes of beta spectra as inputs. For that reason a new setup to measure the shape of the beta spectrum of relevant fission products for the calculation of the antineutrino spectra of reactors has been developed. Some preliminary measurements performed at IGISOL with isotopically clean beams are presented in this contribution.

Isomeric ratios have been measured for high-spin states in Po84198,200,206,208, At85208,209,210,211, Rn86210,211,212,213,214, Fr87208,211,212,213,214, Ra88210,211,212,214,215, and Ac89215 following the projectile fragmentation of a 1 AGeV U beam by a Be target at GSI Helmholtzzentrum für Schwerionenforschung. The fragments were separated in the fragment separator (FRS) and identified by means of energy loss and time-of-flight techniques. They were brought to rest at the centre of the RISING gamma-ray detector array and intensities of gamma rays emitted in the decay of isomeric states with half-lives between 100 ns and 40 μs and spin values up to 55/2ℏ were used to obtain the corresponding isomeric ratios. The data are compared to theoretical isomeric ratios calculated in the framework of the abrasion-ablation model. Large experimental enhancements are obtained for high-spin isomers in comparison to expected values. © 2013 Elsevier B.V.

We report on the observation of Kr-67 that has been produced in an experiment performed at the RIKEN/BigRIPS facility. The two-proton decay of Kr-67 has been evidenced and this nucleus is thus the fourth observed long lived ground-state two-proton emitter, after Fe-45, Ni-48 and Zn-54. In addition, the decay of several isotopes in the mass region has been investigated. While for previous cases of two-proton radioactivity, the theoretical models could reproduce the measured data, this is not the case anymore for Kr-67. Two interpretations have been proposed to explain this discrepancy: a transition between real two-proton and sequential decay or the influence of deformation. These hypotheses will be tested in future experiments by measuring the angular and energy correlations of the emitted protons.

High spin states in the neutron rich 188Os and 190Os nuclei have been populated using the 82Se + 192Os deep-inelastic reaction. The level schemes are extended up to spin I ≈21. The observed new structures are tentatively interpreted as fragments of rotational bands built on multi-quasiparticle configurations.

The β decay of 208Hg into the one-proton hole, one neutron-particle 20881Tl127 nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z

In a nuclear reactor, the decay of fission fragments is at the origin of decay heat and antineutrino flux. These quantities are not well known while they are very important for reactor safety and for our understanding of neutrino physics. One reason for the discrepancies observed in the estimation of the decay heat and antineutrinos flux coming from reactors could be linked with the Pandemonium effect. New measurements have been performed at the JYFL facility of Jyväskylä with a Total Absorption Spectrometer (TAS) in order to circumvent this effect. An overview of the TAS technique and first results from the 2009 measurement campaign will be presented. © Owned by the authors, published by EDP Sciences, 2013.

Relativistic energy projectile fragmentation of Pb-208 has been used to produce a range of exotic nuclei. The nuclei of interest were studied by detecting delayed gamma rays following the decay of isomeric states. Experimental information on the excited states of the neutron-rich N = 126 nucleus, Pt-204, following internal decay of two isomeric states, was obtained for the first time. In addition, decays from the previously reported isomeric I=27h and I=(49/2)h states in Tb-148 and Gd-147, respectively, have been observed. These isomeric decays represent the highest spin discrete states observed to date following a projectile fragmentation reaction, and opens further the possibility of doing 'high-spin physics' using this technique.

Background: Previous measurements of Beta-delayed neutron emitters comprise around 230 nuclei, spanning from the 8He up to 150La. Apart from 210Tl, with a minuscule branching ratio of 0.07%, no other neutron emitter is measured yet beyond A = 150. Therefore new data are needed, particularly in the heavy mass region around N=126, in order to guide theoretical models and to understand the formation of the third r-process peak at A 195. Purpose: To measure both, Beta-decay half-lives and neutron branching ratios of several neutron-rich Au, Hg, Tl, Pb and Bi isotopes beyond N = 126. Method: Ions of interest are produced by fragmentation of a 238U beam, selected and identifed via the GSI-FRS fragment separator. A stack of segmented silicon detectors (SIMBA) is used to measure ion-implants and -decays. An array of 30 3He tubes embedded in a polyethylene matrix (BELEN) is used to detect neutrons with high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time-correlations. The latter are analyzed with an analytical model and results for the half-lives and neutron-branching ratios are derived using the binned Maximum-Likelihood method. Results: Twenty new Beta-decay half-lives are reported for 204

A compact, quasi-4π position sensitive silicon array, TIARA, designed to study direct reactions induced by radioactive beams in inverse kinematics is described here. The Transfer and Inelastic All-angle Reaction Array (TIARA) consists of 8 resistive charge division detectors forming an octagonal barrel around the target and a set of double-sided silicon-strip annular detectors positioned at each end of the barrel. The detector was coupled to the γ-ray array EXOGAM and the spectrometer VAMOS at the GANIL Laboratory to demonstrate the potential of such an apparatus with radioactive beams. The reaction, well known in direct kinematics, has been carried out in inverse kinematics for that purpose. The observation of the ground state and excited states at 7.16 and 7.86 MeV is presented here as well as the comparison of the measured proton angular distributions with DWBA calculations. Transferred l-values are in very good agreement with both theoretical calculations and previous experimental results obtained in direct kinematics.

206Hg was populated in the fragmentation of an E∕A = 1 GeV 208Pb beam at GSI. It was part of a campaign to study nuclei around 208Pb via relativistic Coulomb excitation. The observation of the known isomeric states confirmed the identification of the fragmentation products. The isomeric decays were also used to prove that the correlations between beam identification detectors and the AGATA γ-ray tracking array worked properly and that the tracking efficiency was independent of the time relative to the prompt flash.

The beta-decay of the even-even nucleus Kr-70 with Z=N+2, has been investigated at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center using the BigRIPS fragment separator, the ZeroDegree Spectrometer, the WAS3ABI implantation station and the EURICA HPGe cluster array. Fifteen gamma-rays associated with the beta-decay of( 70)Kr into Br-70 have been identified for the first time, defining ten populated states below E-exc=3300 keV. The half-life of Kr-70 was derived with increased precision and found to be t(1/2)=45.19 +/- 0.14 ms. The beta-delayed proton emission probability has also been determined as epsilon(p)=0.545(23)%. An increase in the beta-strength to the yrast 1(+) state in comparison with the heaviest Z=N+2 system studied so far (Ge-62 decay) is observed that may indicate increased np correlations in the T=0 channel. The beta-decay strength deduced from the results is interpreted in terms of the proton-neutron quasiparticle random-phase approximation (pnQRPA) and also with a schematic model that includes isoscalar and isovector pairing in addition to quadrupole deformation. The application of this last model indicates an approximate realization of pseudo-SU(4) symmetry in this system. (C) 2022 The Author(s). Published by Elsevier B.V.

The β decays of more than twenty fission fragments were measured in the first experiments with radioactive-ion beams employing the Decay Total Absorption γ-ray Spectrometer. In this work, we summarize the main results obtained so far from this experimental campaign carried out at the Ion Guide Isotope Separator On-Line facility. The advances introduced for these studies represent the state-of-the-art of our analysis methodology for segmented spectrometers.

We report here the results of a study of the beta decay of the proton-rich Ge isotopes, Ge-60 and Ge-62, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of Ge-62 [73.5(1) ms] and Ge-60 [25.0(3) ms] and its daughter nucleus, Ga-60 [69.4(2) ms]. We measured individual beta-delayed proton and gamma emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total beta-delayed proton-emission branching ratio of 67(3)% has been obtained for Ge-60. New information has been obtained on the energy levels populated in Ga-60 and on the 1/2(-) excited state in the beta p daughter Zn-59. We extracted a ground state-to-ground state feeding of 85.3(3)% for the decay of Ge-62. Eight new y lines have been added to the deexcitation of levels populated in the Ga-62 daughter.

During the last decade we have carried out a systematic study of the β decay of neutron-deficient nuclei, providing rich spectroscopic information of importance for both nuclear structure and nuclear astrophysics. We present an overview of the most relevant achievements, including the discovery of a new exotic decay mode in the fp-shell, the β-delayed γ-proton decay in ⁵⁶Zn, the first observation of the 2⁺ isomer in ⁵²Co and the latest results on the heavier systems ⁶⁰Ge and ⁶²Ge. We also report on our deduced mass excesses in comparison with systematics and a recent measurement. Finally, we summarise our results on the half-lives of Tz -1/2, -1 and -2 neutron-deficient nuclides, and analyse their trend.

The accurate determination of reactor antineutrino spectra remains a very hot research topic, where new questions have emerged in recent years. Indeed, after the "reactor anomaly" - a deficit of measured antineutrinos at short baseline reactor experiments with respect to spectral predictions - the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have evidenced spectral distortions in their measurements with respect to the same spectral predictions. This puzzle is called the "shape anomaly". Recently summation calculations of reactor antineutrino spectra based on the use of nuclear data have obtained the best agreement to date with the reactor neutrino flux measurements at the level of 2% thanks to a decade of Total Absorption Gamma-ray Spectroscopy (TAGS) measurements at the radioactive beam facility of the University of Jyvaskyla in two experimental campaigns. A selection of the results obtained so far is presented.

High-spin states in the proton-rich nucleus 45V have been identified for the first time. A comprehensive gamma-ray decay scheme has been established following an experiment performed at the Vivitron accelerator at IReS Strasbourg by using the Euroball gamma-ray detector array coupled to the Neutron Wall and Euclides detector arrays. The natural (negative-) parity scheme is identified up to the f7/2 band termination in addition to a positive-parity collective structure based on a d3/2 particle-hole excitation. Comparison of this scheme with that of the mirror partner, 45Ti, has yielded detailed information on the variation of Coulomb energy as a function of excitation energy and angular momentum. This is the first time that such an analysis has been performed for a collective structure built on a cross-shell excitation. Comparison of the observed Coulomb energies with those predicted by large-scale shell-model calculations is presented. In this case, unusually, the calculations do not fare as well as for heavier nuclei in the shell. In addition, stark differences between the two nuclei are observed for the decay intensities of the parity-changing E1 decays that de-excite the positive-parity deformed bands.

Picosecond lifetimes of medium spin states in Lu-165 were measured for the first time. The reaction used to populate the nucleus of interest was La-139(Si-30,4n)Lu-165 at a beam energy of 135 MeV. The beam was provided by the XTU-tandem accelerator of Laboratori Nazionali di Legnaro, Italy. By using the differential decay curve method, lifetimes of 19 states in four different rotational bands were obtained. Therefrom the B(E2) values and the transitional quadrupole moments were deduced. The obtained Q(t) for the different bands are compared with total Routhian surface (TRS) calculations and particle-rotor-model calculations. The TRS calculations predict different axial symmetric shapes for the bands built on the 9/2(-)[514], 9/2(+)[404], and 1/2(-)[541] configurations, with a gamma softness for the 9/2(-)[514] configuration. This band has also been studied using the particle-rotor model, the results of which, however, are consistent with a triaxial shape with a gamma value of -15(p).

decays from heavy, neutron-rich nuclei with A∼190 have been investigated following their production via the relativistic projectile fragmentation of an E/A=1 GeV 208Pb primary beam on a ∼2.5 g/cm2 9Be target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper. γ decays were observed and correlated with these secondary ions on an event-by-event basis such that γ-ray transitions following from both internal (isomeric) and β decays were recorded. A number of discrete, β-delayed γ-ray transitions associated with β decays from 194Re to excited states in 194Os have been observed, including previously reported decays from the yrast Iπ=(6+) state. Three previously unreported γ-ray transitions with energies 194, 349, and 554 keV are also identified; these transitions are associated with decays from higher spin states in 194Os. The results of these investigations are compared with theoretical predictions from Nilsson multi-quasiparticle (MQP) calculations. Based on lifetime measurements and the observed feeding pattern to states in 194Os, it is concluded that there are three β−-decaying states in 194Re.

Gamow-Teller β decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This Δn=0 requirement plays a major role in the β decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical r-process pathway below both Z=50 (for N ˃ 82) and Z = 82 (for N ˃ 126). The level of forbiddenness of the Δn=1v1g9/2 → π0g7/2 transition has been investigated from the β decay of the ground state of 207Hg into the single-proton-hole nucleus 207Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible γ-ray transitions depopulating the π0g-17/2 state in 207Tl, an upper limit of 3.9 x 10-3% was obtained for the probability of this decay, corresponding to log ft ˃ 8.8 within a 95% confidence limit. This is the most stringent test of the Δn=0 selection rule to date.

Neutron-rich nuclei were populated in a relativistic fission of U. Gamma-rays with energies of 135 keV and 184 keV were associated with two isomeric states in Pd and Ru. Half-lives of 0.63(5) μs and 2.0(3) μs were deduced and the isomeric states were interpreted in terms of prolate deformed single-particle states.

The β decay of 207Hg into the single-proton-hole nucleus 207Tl has been studied through γ-ray spectroscopy at the ISOLDE Decay Station (IDS) with the aim of identifying states resulting from coupling of the πs−11/2, πd−13/2, and πh−111/2 shell model orbitals to the collective octupole vibration. Twenty-two states were observed lying between 2.6 and 4.0 MeV, eleven of which were observed for the first time, and 78 new transitions were placed. Two octupole states (s1/2-coupled) are identified and three more states (d3/2-coupled) are tentatively assigned using spin-parity inferences, while further h11/2-coupled states may also have been observed for the first time. Comparisons are made with state-of-the-art large-scale shell model calculations and previous observations made in this region, and systematic underestimation of the energy of the octupole vibrational states is noted. We suggest that in order to resolve the difference in predicted energies for collective and noncollective t=1 states (t is the number of nucleons breaking the 208Pb core), the effect of t=2 mixing may be reduced for octupole-coupled states. The inclusion of mixing with t=0,2,3 excitations is necessary to replicate all t=1 state energies accurately.

We have developed a new experimental setup based at the GANIL/SPIRAL facility in Caen, France to measure one-nucleon transfer reactions in inverse kinematics in order to study the evolution of the single particle structure of exotic nuclei. The setup couples together three state-of-the-art detection systems: the TIARA Si array, the large-acceptance magnetic spectrometer VAMOS and the high-efficiency segmented Ge γ-ray array EXOGAM. In a first experiment, the 24Ne(d,p)25Ne reaction has been studied to probe the N=16 shell closure. Details of the setup, data analysis and preliminary results are presented. © 2006 American Institute of Physics.

The preliminary results from the RISING Stopped Beam Isomer Campaign are presented, with specific focus on results of the initial experiment to investigate isomeric decays along the N=Z line around A similar to 80-90 following the projectile fragmentation of a Ag-107 primary beam at an energy of 750 MeV per nucleon. A description of the technical aspects behind the design of the RISING array is presented, together with evidence for previously unreported isomeric decays in Tc-87,Tc-88 and the N=Z nuclei Nb-82(41) and Tc-86(43).

The TIARA+VAMOS+EXOGAM set-up has recently been installed at GANIL to study the single-particle structure of exotic nuclei. The unique characteristics of the TIARA array, combined with the large acceptance spectrometer VAMOS and the high efficiency Germanium detector array EXOGAM, has allowed high-resolution measurements of transfer reactions in inverse kinematics using low intensity exotic beams. We will describe the experimental set-up, data analysis and preliminary results of the first experiments using a 24Ne beam from SPIRAL, concentrating in particular on the performance of VAMOS that has been used to detect the heavy fragments after the (d,p), (d,d) and (d,t) reactions. © 2006 American Institute of Physics.

The β decays of the ground state (gs) and isomeric state (m) of Y 96 have been studied with the total absorption γ-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility. The separation of the 8+ isomeric state from the 0− ground state was achieved thanks to the purification capabilities of the JYFLTRAP double Penning trap system. The β-intensity distributions of both decays have been independently determined. In the analyses the deexcitation of the 1581.6 keV level in Zr96, in which conversion electron emission competes with pair production, has been carefully considered and found to have significant impact on the β-detector efficiency, influencing the β-intensity distribution obtained. Our results for Y 96gs (0−) confirm the large ground state to ground state β-intensity probability, although a slightly larger value than reported in previous studies was obtained, amounting to 96.6−2.1+0.3% of the total β intensity. Given that the decay of Y 96gs is the second most important contributor to the reactor antineutrino spectrum between 5 and 7 MeV, the impact of the present results on reactor antineutrino summation calculations has been evaluated. In the decay of Y 96m (8+), previously undetected β intensity in transitions to states above 6 MeV has been observed. This shows the importance of total absorption γ-ray spectroscopy measurements of β decays with highly fragmented deexcitation patterns. Y 96m (8+) is a major contributor to reactor decay heat in uranium-plutonium and thorium-uranium fuels around 10 s after fission pulses, and the newly measured average β and γ energies differ significantly from the previous values in evaluated databases. The discrepancy is far above the previously quoted uncertainties. Finally, we also report on the successful implementation of an innovative total absorption γ-ray spectroscopy analysis of the module-multiplicity gated spectra, as a first proof of principle to distinguish between decaying states with very different spin-parity values.

A total absorption spectrometer, dedicated to the study of very short-lived atomic species, has been built and installed at the CERN/ISOLDE mass separator. The beta decay of the neutron-deficient Kr-74 nucleus has been studied using this new device. The Gamow-Teller strength distribution has been observed over most of the Q(EC) window, and a total strength of 0.69(3) g(A)(2)/4pi has been measured for states with excitation energy below 3 MeV. Shape mixing in the Kr-74 ground state is inferred from a comparison of the experimental strength distribution with self-consistent, deformed, quasiparticle-random-phase-approximation calculations.

We report the results of an experiment in which we studied the near-yrast states in selenium isotopes approaching N=50 following their population in multinucleon transfer reactions between a Se-82 beam and a Os-192 target. The level schemes for Se-80,Se-82 derived from the current work are compared with restricted-basis shell-model calculations and pair-truncated shell-model calculations. These provide a good description of the yrast sequences in these nuclei using a basis space limited to excitations in the nu(p3/2, p1/2, p1/2) and pi(f5/2, p3/2, p1/2) orbitals.

Nucleosynthesis in Type I X-ray bursts (XRB) proceeds eventually through the rp-process near the proton drip-line. Several N=Z nuclei act as waiting points in the reaction network chain. Astrophysical calculations of XRB light curves depend upon the theoretical modelling of the beta decays of interest, with the N=Z waiting points Ge-64, Se-68, Kr-72, Sr-76, and their second-neighbours N=Z+2 being key nuclei in this context. We have carried out different experimental campaigns at ISOLDE (CERN) to determine the B(GT) distributions, in the decay of several N=Z, N=Z+2 and their daughters, of particular relevance in rp-process calculations. To this aim the Total Absorption Spectroscopy technique is applied. Here we present results on the beta decay of Ga-64 and the status of the analysis of Ge-64. Our results provide benchmarks for testing and constraining models under terrestrial conditions that can be used later for predictions in stellar environments.

A multinucleon transfer reaction between a thin self-supporting 78198Pt target and an 850 MeV 54136X6 beam has been used to populate and study the structure of the N=80 isotone 56136Ba. Making use of time-correlated γ-ray spectroscopy, evidence for an Iπ=(10+) isomeric state has been found with a measured half-life of 91±2 ns. Prompt-delayed correlations have also enabled the tentative measurement of the near-yrast states which lie above the isomer. Shell-model calculations suggest that the isomer has a structure which can be assigned predominantly as (vh 11/2)10+-2. The results are discussed in terms of standard and pair-truncated shell-model calculations, and compared to the even-Z N=80 isotones ranging from 50130Sn to 68148Er. A qualitative explanation of the observed dramatic decrease in the B(E2:10+→8+) value for the N=80 isotones at 136Ba is given in terms of the increasing single-hole energy of the h11/2 neutron configuration as the proton subshell is filled. The angular momentum transfer to the binary fragments in the reaction has also been investigated in terms of the average total γ-ray fold versus the scattering angle of the recoils.

To study the β-decay properties of some well known delayed neutron emitters an experiment was performed in 2009 at the IGISOL facility (University of Jyväskylä in Finland) using Total Absorption -ray Spectroscopy (TAGS) technique. The aim of these measurements is to obtain the full β-strength distribution below the neutron separation energy (Sn) and the γ/neutron competition above. This information is a key parameter in nuclear technology applications as well as in nuclear astrophysics and nuclear structure. Preliminary results of the analysis show a significant γ-branching ratio above Sn. © Owned by the authors, published by EDP Sciences, 2014.

Heavy neutron-rich nuclei were populated via relativistic energy fragmentation of a E/A=1 GeV 208Pb beam. The nuclei of interest were selected and identified by a fragment separator and then implanted in a passive plastic stopper. Delayed rays following internal isomeric decays were detected by the RISING array. Experimental information was obtained on a number of nuclei with Z=73-80 (Ta-Hg), providing new information both on the prolate-oblate transitional region as well as on the N=126 closed shell nuclei.

Preliminary results of the data analysis of the beta decay of 94Rb using a novel - segmented- total absorption spectrometer are shown in this contribution. This result is part of a systematic study of important contributors to the decay heat problem in nuclear reactors. In this particular case the goal is to determine the beta intensity distribution below the neutron separation energy and the gamma/beta competition above. © 2013 AIP Publishing LLC.

This contribution summarizes an experiment performed at GSI (Germany) in the neutron-rich region beyond N=126. The aim of this measurement is to provide the nuclear physics input of relevance for r-process model calculations, aiming at a better understanding of the third r-process abundance peak. Many exotic nuclei were measured around 211Hg and 215Tl. Final ion identification diagrams are given in this contribution. For most of them, we expect to derive halflives and and β-delayed neutron emission probabilities. The detectors used in this experiment were the Silicon IMplantation and Beta Absorber (SIMBA) detector, based on an array of highly segmented silicon detectors, and the BEta deLayEd Neutron (BELEN) detector, which consisted of 30 3He counters embedded in a polyethylene matrix. © 2013 AIP Publishing LLC.

The spins and parities of low-lying states in 72 Br populated in the beta decay of 72 Kr have been 14 studied via conversion electron spectroscopy. The measurements were carried out at ISOLDE using 15 a mini-orange spectrometer with Si(Li) and HPGe detectors for electrons and γ-rays detection. 16 Results of the conversion coefficients corresponding to transitions de-exciting 12 levels in 72 Br are 17 reported. The multipolarities of the transitions are deduced and the spins and parities of the levels 18 involved are discussed. From the multipolarities of the most intense transitions to the ground state, 19 the spin and parity of the 72 Br ground state have been definitely established as 1 +. The spin of 20 the 101.2-keV isomeric state is determined to be 3 −. The level scheme is compared with mean-field 21 and shell-model calculations and oblate deformation for the 72 Br ground state is deduced. No E0 22 transitions have been found in 72 Br. E0 transitions in the neighbouring isobaric nuclei, 72 Se and 23 72 Ge, have also been studied. 24

Understanding the β-decay properties of fission products is very important for nuclear reactor monitoring & safety. Indeed, the β-decay of fission products is a source of power during nuclear reactor operation and after, this activity is the main contributor to the decay-heat representing ∼7-8% of a reactor nominal power. β-decay is also at the origin of the antineutrinos coming from nuclear reactor. The study of antineutrinos is mandatory for nuclear safeguard policies based on antineutrino detection. But there are still some discrepancies in the calculation of the decay-heat and antineutrino spectra. One reason of the distortions observed seems to be linked to the Pandemonium effect. In order to improve the accuracy in the prediction of these quantities, new measurements of fission products β-decay properties, not sensitive to this effect, have been performed with a Total Absorption spectrometer (TAS). An overview of the TAS technique and first results from the latest experiment will be presented. © 2013 IEEE.

We investigate the decay of 87,88Br and 94Rb using total absorption γ -ray spectroscopy. These important fission products are β-delayed neutron emitters. Our data show considerable βγ intensity, so far unobserved in high-resolution γ -ray spectroscopy, from states at high excitation energy. We also find significant differences with the β intensity that can be deduced from existing measurements of the β spectrum. We evaluate the impact of the present data on reactor decay heat using summation calculations. Although the effect is relatively small it helps to reduce the discrepancy between calculations and integral measurements of the photon component for 235U fission at cooling times in the range 1–100 s. We also use summation calculations to evaluate the impact of present data on reactor antineutrino spectra. We find a significant effect at antineutrino energies in the range of 5 to 9 MeV. In addition, we observe an unexpected strong probability for γ emission from neutron unbound states populated in the daughter nucleus. The γ branching is compared to Hauser-Feshbach calculations, which allow one to explain the large value for bromine isotopes as due to nuclear structure. However the branching for 94Rb, although much smaller, hints of the need to increase the radiative width γ by one order of magnitude. This increase in γ would lead to a similar increase in the calculated (n,γ ) cross section for this very neutron-rich nucleus with a potential impact on r process abundance calculations.