Professor Wilton Catford

The astrophysical 25Al(p,γ)26Si reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic 26Al ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in 26Si, that govern the rate of the 25Al(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the 26Si mirror nucleus 26Mg. We have measured the lifetime of the 3+, 6.125-MeV state in 26Mg to be 19(3)fs and provide compelling evidence for the existence of a 1− state in the T=1,A=26 system, indicating a previously unaccounted for ℓ=1 resonance in the 25Al(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1− state corresponds to a resonance in the 25Al+p system at 435.7(53) keV, we find considerable differences in the 25Al(p,γ) reaction rate compared to previous works. Based on current nova models, we estimate that classical novae may be responsible for up to ≈15% of the observed galactic abundance of 26Al. peerReviewed

We present new experimental measurements of resonance strengths in the astrophysical $^{23}$Al(p,γ)$^{24}$Si reaction, constraining the pathway of nucleosynthesis beyond $^{22}$Mg in X-ray burster scenarios. Specifically, we have performed the first measurement of the (d,p) reaction using a radioactive beam of $^{23}$Ne to explore levels in $^{24}$Ne, the mirror analog of $^{24}$Si. Four strong single-particle states were observed and corresponding neutron spectroscopic factors were extracted with a precision of ∼20%. Using these spectroscopic factors, together with mirror state identifications, we have reduced uncertainties in the strength of the key ℓ = 0 resonance at Er = 157 keV, in the astrophysical $^{23}$Al(p,γ) reaction, by a factor of 4. Our results show that the $^{22}$Mg(p,γ)$^{23}$Al(p,γ) pathway dominates over the competing $^{22}$Mg(α,p) reaction in all but the most energetic X-ray burster events (T>0.85 GK), significantly affecting energy production and the preservation of hydrogen fuel.

The astrophysical Al25(p,γ)Si26 reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic Al26 ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in Si26, that govern the rate of the Al25(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the Si26 mirror nucleus Mg26. We have measured the lifetime of the 3+, 6.125-MeV state in Mg26 to be 19(3)fs and provide compelling evidence for the existence of a 1- state in the T=1,A=26 system, indicating a previously unaccounted for=1 resonance in the Al25(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1- state corresponds to a resonance in the Al25+p system at 435.7(53) keV, we find considerable differences in the Al25(p,γ) reaction rate compared to previous works. Based on current nova models, we estimate that classical novae may be responsible for up to ≈15% of the observed galactic abundance of Al26. This work was supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract No. DEAC02-06CH11357 and Grants No. DEFG02-94-ER40834, No. DEFG02-97-ER41041, No. DEFG02-97-ER41043, and No. DE-FG02-93ER4077. U.K. personnel were supported by the Science and Technologies Facilities Council (STFC). This work was partially supported by the Spanish MINECO Grant No. AYA2017-86274-P, by the E.U. FEDER funds, and by the AGAUR/Generalitat de Catalunya Grant No. SGR-661/2017. This article benefited from discussions within the “ChETEC” COST Action (Grant No. CA16117). This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User facility.

Abstract The nuclear matter and charge radii of the helium isotopes (A = 4,6,8) are calculated by quantitative geometrical thermodynamics (QGT) taking as input the symmetry of the alpha-particle, the very weak binding (and hence halo nature) of the heavier helium isotopes, and a characteristic length scale given by the proton size. The results follow by considering each isotope in its ground state, with QGT representing each system as a maximum entropy configuration that conforms to the Holographic Principle. This allows key geometric parameters to be determined from the number of degrees of freedom available. QGT treats 6He as a 4He core plus a concentric neutron shell comprising a holomorphic pair of neutrons, and the 8He neutron halo is treated as a holomorphic pair of holomorphic pairs. Considering the information content of each system allows a correlation angle of 2pi/3 between the holomorphic entities to be inferred, and then the charge radii of the three isotopes can be calculated from the displacement of the 4He core from the centre of mass. The calculations for the charge and matter radii of 4,6,8He agree closely with observed values. Similar QGT calculation of the sizes of the self-conjugate A = 4n nuclei {4He,8Be,12C,16O,20Ne,24Mg,28Si,32S,36Ar,40Ca} also agree well with experiment.

BlueSTEAl, the Blue (aluminum chamber of) Silicon TElescope Arrays for light nuclei, has been developed to study direct reactions in inverse kinematics, as well as scattering and breakup reactions using radioactive ion beams. It is a detector system consisting of a pair of annular silicon detector arrays and a zero-degree phoswich plastic scintillator. For typical binary reaction studies in inverse kinematics, light ions are detected by the Si array in coincidence with heavy recoils detected by the phoswich placed at the focal-plane of a zero-degree magnetic spectrometer. The Si array can also be used to detect light nuclei such as beryllium and carbon with clear isotope separation, while the phoswich can also be placed at zero degrees without a spectrometer and used as a high-efficiency beam counting monitor with particle identification capability at the rate of up to ~5 × 104 particles per second. This paper reports on the capabilities of BlueSTEAl as determined by recent experiments performed at the Texas A&M Cyclotron Institute. Furthermore, the device is also anticipated to be used in future experiments at other radioactive ion beam facilities.

The low-lying structure of 15C has been investigated via the neutron-removal d(16C, t) reaction. The experiment was performed at GANIL using a secondary 16C beam produced by fragmentation in the LISE spectrometer at 17.2 MeV/nucleon with an intensity of 5 × 104 pps and 100% purity. The angle and energy of the light ejectile were detected by three MUST2 telescopes. The missing mass technique was used to reconstruct the excitation energy of 15C. In this spectrum, two bound states were observed (gs and the first excited state) and two unbound resonant states above the neutron separation threshold (S n = 1.218 MeV). From the differential cross sections, information on the angular momentum of the transferred nucleon and spectroscopic factors were deduced.The excitation energies and the deduced spectroscopic factors of the negative parity states placed above the neutron separation energy are an important measurement of the 2p-1h configurations in 15C. Our results show good agreement with shell-model calculations with the YSOX interaction and show a sensitivity to the N=8 shell gap.

13 pags., 8 figs., 1 tab. We measured 135 cross sections of residual nuclei produced in fragmentation reactions of C12, N14, and O13−16,20,22 projectiles impinging on a carbon target at kinetic energies of near 400A MeV, most of them for the first time, with the RB3/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below 20% for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations. This work has been partially supported by the Spanish Ministry for Science and Innovation under Grants No. PGC2018-099746-B-C21, No. PGC2018-099746-B-C22, and No. PID2019-104390GB-100; Xunta de Galicia under program “Grupos de referencia competitiva” (Project No. ED431C 2017/54); the German Bundesministerium für Bildung und Forschung (BMBF) (Grants No. 05P12RDFN8, No. 05P15RDFN1, and No. 05P19RDFN); the Swedish Research Council; and U.S. Department of Energy Grant No. DE-FG02-08ER41533. J.J.R.S. acknowledges the support of Xunta de Galicia under Grant No. ED481B-2017/002. Peer reviewed

The pygmy dipole resonance (PDR) has been the subject of numer-ous studies, both experimental and theoretical. Indeed, the study of the PDR has been and still is of great interest since it allows to constrain the symmetry energy, an important ingredient of the equation of state of nuclear matter that describes the matter within neutron stars. Moreover, the PDR is predicted to play a key role in the r-pro cess via the increase of the neutron capture rate. However, despite numerous experiments dedicated to the study of the PDR, a consistent description is still missing. In this context, we have proposed to study the PDR using a new probe: the neutron inelastic scattering reaction (n,n'-y). An experiment to study the pygmy resonance in 140Ce using the (n,n'-y) reaction has been performed in Septem-ber 2022. This experiment has been made possible thanks to the high-intensity proton beam of the new accelerator SPIRAL2 at GANIL and the NFS (Neutron For Science) facility. The experimental setup was composed of the new generation multi-detectors PARIS, for the detection of-y-rays coming from the de-excitation of the PDR, and MONSTER, for the detection of scattered neutrons. In this article, the experiment motivation and description are presented.

The isovector and isoscalar components of neutron-proton pairing are investigated in the N=Z unstable nuclei of the fp-shell through the two-nucleon transfer reaction (p,$^{3}$He) in inverse kinematics. The combination of particle and gamma-ray detection with radioactive beams of $^{56}$Ni and $^{52}$Fe, produced by fragmentation at the GANIL/LISE facility, made it possible to carry out this study for the first time in a closed and an open-shell nucleus in the fp-shell. The transfer cross-sections for ground-state to ground-state (J=0$^{+}$, T=1) and to the first (J=1$^{+}$, T=0) state were extracted for both cases together with the transfer cross-section ratios σ(0+,T=1)/σ(1+,T=0). They are compared with second-order distorted-wave born approximation (DWBA) calculations. The enhancement of the ground-state to ground-state pair transfer cross-section close to mid-shell, in $^{52}$Fe, points towards a superfluid phase in the isovector channel. For the “deuteron-like” transfer, very low cross-sections to the first (J=1$^{+}$, T=0) state were observed both for $^{56}$Ni(p,$^{3}$He) and $^{52}$Fe(p,$^{3}$He) and are related to a strong hindrance of this channel due to spin-orbit effect. No evidence for an isoscalar deuteron-like condensate is observed.

Monte Carlo simulations are widely used in nuclear physics to model experimental systems. In cases where there are significant unknown quantities, such as energies of states, an iterative process of simulating and fitting is often required to describe experimental data. We describe a Bayesian approach to fitting experimental data, designed for data from a 12Be(d,p) reaction measurement, using simulations made with GEANT4. Q-values from the 12C(d,p) reaction to well-known states in 13C are compared with simulations using BayesOpt. The energies of the states were not included in the simulation to reproduce the situation for 13Be where the states are poorly known. Both cases had low statistics and significant resolution broadening owing to large proton energy losses in the solid deuterium target. Excitation energies of the lowest three excited states in 13C were extracted to better than 90 keV, paving a way for extracting information on 13Be.

The mean life of the 2795 keV 1 + 2 level in 21Ne has been measured using the 21C( 13C, αγ) 21Ne reaction and a variant of the Doppler-shift attenuation method. The result obtained was τ = 7.9 ± 1.8 fs. In addition, the separation of the 2789 ( 1 − 2) and 2795 ( 1 + 2 ) keV levels in 21Ne been measured as 5.91 ± 0.31 keV. The relevance of both results to measurements of parity mixing in 21Ne is discussed.

The lowest 0 +; T = 2 state in 40Ca has been excited as a resonance in 36Ar(α,γ) 40Ca at E x = 11988±2 keV; г p1 has been determined and limits placed on Γ, Γ p 2 , Γ p 3 and Γ α 1 . Transitions to 1 +; T = 1 levels at 10321.0 ± 1.6 keV and 9868.0 ± 1.7 keV were observed and their strengths measured. Ground-state M1 strength from 1 +; T = 1 levels is inferred.

The mass of the proton-rich nucleus 39Sc has been derived from a measurement of the Q-value of the 40Ca( 14N, 15O) 39Sc reaction at a beam energy of 102.5 MeV and mean reaction angle of 6°. A value of −27.67 ±0.03 MeV was obtained for the Q-value, implying a mass excess of −14.19 ± 0.03 MeV for the ground state of 39Sc, which is therefore unbound to proton emission by an energy of 580 ±30 keV. There is some evidence for an excited state in 39Sc at an energy of 950 ±keV. This state is tentatively identified as the analog of the 1.27 MeV 3 2 − state in 39Ar. The cross sections to the 1 2 + and 5 2 + states in 15C confirm an earlier suggestion that this reaction is well suited to the observation of proton-rich nuclei via direct transfer reactions having very negative Q-values.

The reaction 19F( 6Li, d) 23Na has been studied at a beam energy of 34 MeV using a high resolution magnetic spectrometer. A total of 36 states in 23Na have been observed in the range E x = 4–13MeV and deuteron angular distributions obtained for 26 states. Compound processes accounted for less than 10% of the forward angle cross section in most instances. Finite-range distorted-wave Born approximation calculations have been performed and compared with the data. The calculations reproduced the observed angular distributions well, allowing relative α-particle spectroscopic factors to be extracted and several new or improved spin assignments to be made. The 6Li- 19F optical potential was derived from elastic scattering data obtained in the present work. The results are discussed with reference to the rotational structure of 23Na.

The status of the mirror state in 9B of the first excited 1 2 + 1.68 MeV state in 9Be is reviewed. The experimental evidence is inconclusive except for an apparent peak recently reported in a spectrum from the 9Be( 6Li, 6He) 9B reaction. This reaction has been reinvestigated at the same energy and angle but with substantially improved resolution and statistics, and the present results provide no evidence for the previously reported peak. Spectra obtained at other energies and angles have very low background and yet similarly fail to exhibit a peak. In addition, no evidence for population of the mirror state is found in spectra taken for the reaction 10B( 9Be, 10Be) 9B at two bombarding energies. The energy and width of the expected 1 2 + state in 9B remain open questions for which several different theoretical descriptions offer quite different predictions.

The partial widths for α-particle and γ-ray decay of the second 2 + T = 1 level in 20Ne at 12.22 MeV have been measured. The reaction 19F( 3He, d) 20Ne was employed, with deuterons detected in singles and in coincidence with γ-rays from the decay of the 12.22 MeV level. The coincidence efficiency was determined using the 100% γ-decay of the 10.89 MeV 3 + T = 1 level. The ratio of the γ-decay width to the total width of the 12.22 MeV level was measured to be 0.88 ±0.05, which combined with a recent 16 O(α, γ) 20Ne measurement yields a very small α-particle width of 0.32±0.06 eV. This result is also of relevance to the radiative decay of the 18.43 MeV 2 + T = 2 level in 20Ne, and confirms a large discrepancy between the measured γ-decay width of the 2 + T = 2 level and the predictions of the shell model.

The mass excess of 35Si has been determined as −14.427 ± 0.060 MeV from a measurement employing the 36S( 13C, 14O) 35Si reaction. No excited states of 35Si were observed. The 34S( 13C, 14O) 33Si reaction was studied simultaneously, and previously unreported excited states in 33Si were observed at 1.47, 2.00, 3.19, 4.13 and 5.48 MeV.

States with excitation energy > 15 MeV populated in the reaction 12C( 16O, αγ) 24Mg have been studied using a total energy γ-ray spectrometer for E lab( 16 O) between 40 and 67 MeV. A previously unknown state has been identified at 16.904 ± 0.003 MeV with Γ γ / Γ=0.13±0.02, mean lifetime

The multinucleon transfer reactions 18O( 18O, 17F) 19N and 18O( 18O, 15O) 21O have been studied at a beam energy of 117 MeV and a mean reaction angle of 10°. The same reactions, but detecting the neutron-rich ejectiles, have also been studied at a mean angle of 4.5°. Excitation energies for low-lying levels in the two T z = 5 2 nuclei 19N and 21O have been derived. The correspondence between the observed levels and those predicted by 0kh ω shell-model calculations is discussed. The proposed level assignments are deduced by analogy with results from the 16O( 18O, 17F) 17N and 16O( 18O, 15O) 19O reactions, which were also studied in the present work, and are supported by calculations employing a semi-classical reaction model.

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.

A measurement of low-lying states in B-9 was conducted using the Li-6(Li-6,t)B-9 reaction at a beam energy of 56 MeV. The particles resulting from the decay of B-9 into Be-8 + p were detected with position sensitive detectors, and relative energy spectra were obtained from the data using the technique of resonant particle decay spectroscopy. This technique provided a very low background, and the ability to separate the B-9 states that decay by Be-8 + p from those that decay by Li-5 + alpha. Results show that a significant portion of the measured spectrum below approximate to 1.5 MeV cannot be explained by the known states which suggests that these counts arise from the mirror of the 1.68 MeV 1+/2 state of Be-9. It was also shown that the recently observed 1-/2 state decays via the p + Be-8 channel.

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 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.

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.

The potential of nucleon transfer experiments using radioactive beams is described, and set in the context of the new experimental challenges and the first reported experiments. Particular attention is paid to the requirements imposed on experiments by studying reactions in inverse kinematics on very light targets.

Spectroscopic data, such as precise γ-ray branching and E2/M1 multipole-mixing ratios, provide vital constraints when performing multi-dimensional Coulomb-excitation analyses. Consequently, as part of our new Coulomb-excitation campaign aimed at investigating the role of exotic non-axial (triaxial) deformations in the unstable refractory Ru-Mo isotopes, additional beta-decay data was obtained. These measurements make use of ANL's CARIBU facility, which provides intense beams of radioactive refractory isotopes along with the excellent efficiency and angular resolution of the GRETINA γ-ray tracking array. In this article, we report on the analysis of the A = 110 decay chain, focussing on the identification of previously unreported states in 110Ru following the decay of 110Tc.

The nuclear structure of the 31Mg nucleus has been studied with the single-neutron knockout reaction. We report on the preliminary results of an experiment performed with the EXOGAM array coupled, for the first time, to the SPEG spectrometer at GANIL. We present a provisional result for the inclusive single-neutron knockout cross section of σinc= 90(5) mb. Preliminary exclusive cross sections for the measured bound states, including the ground state, are also presented. Finally, preliminary longitudinal momentum distributions for the ground state and first excited state are also shown. These results are compared to Monte Carlo Shell-Model calculations in the sd-pf region.

Neutron-rich 34,35Al isotopes have been studied through Coulomb excitation using LAND-FRS setup at GSI, Darmstadt. The method of invariant mass analysis has been used to reconstruct the excitation energy of the nucleus prior to decay. Comparison of experimental CD cross-section with direct breakup model calculation with neutron in p3/2 orbital favours 34Al(g.s) - νp3/2 as ground state configuration of 35Al. But ground state configuration of 34Al is complicated as evident from γ-ray spectra of 33Al after Coulomb breakup of 34Al. © Owned by the authors, published by EDP Sciences, 2014.

An experimental spectroscopic investigation of some neutron rich Mg and Al isotopes around the shell closure N=20 has been performed. The delayed neutron and γ spectra, following the β-decay of 33Mg and 35Al have been measured using the delayed neutron detector array TONNERRE coupled with high efficiency EXOGAM clover detectors, a LEPS detector and eight low-energy neutron detectors. A detailed analysis of such spectra allows one to construct the level schemes of their daughters, 32,33Al and 34,35Si. The resulting spectroscopic information will provide stringent tests of large scale shell model calculations including np - nh excitations aimed at the understanding of the structural effects occurring in this region. © 2006 American Institute of Physics.

We propose to install a storage ring at an ISOL-type radioactive beam facility for the first time. Specifically, we intend to setup the heavy-ion, low-energy ring TSR at the HIE-ISOLDE facility in CERN, Geneva. Such a facility will provide a capability for experiments with stored secondary beams that is unique in the world. The envisaged physics programme is rich and varied, spanning from investigations of nuclear ground-state properties and reaction studies of astrophysical relevance, to investigations with highly-charged ions and pure isomeric beams. The TSR might also be employed for removal of isobaric contaminants from stored ion beams and for systematic studies within the neutrino beam programme. In addition to experiments performed using beams recirculating within the ring, cooled beams can also be extracted and exploited by external spectrometers for high-precision measurements. The existing TSR, which is presently in operation at the Max-Planck Institute for Nuclear Physics in Heidelberg, is well-suited and can be employed for this purpose. The physics cases as well as technical details of the existing ring facility and of the beam and infrastructure requirements at HIE-ISOLDE are discussed in the present technical design report.

We discuss the use of one-nucleon removal reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. The breakup reactions are proved to be good spectroscopic tools and can be used to study a large number of loosely bound proton- or neutron-rich nuclei over a wide range of beam energies. As peripheral processes, they can be used to extract asymptotic normalization coefficients (ANCs) from which non-resonant capture reaction rates of astrophysical interest can be calculated parameter free. In this talk, we present results of a proton-breakup experiment carried out at GANIL (France) with a cocktail beam centered around 23Al at 50 MeV/nucleon. Momentum distributions of the breakup fragments, inclusive and in coincidence with gamma rays detected by EXOGAM Germanium clover array, were measured in the focal plan of SPEG energy-loss spectrometer. We present in particular the investigations of reaction rates for 22Mg(p,γ)23Al and 23Al(p,γ)24Si important for novae and X-ray bursts, respectively.

First results are reported on the ground state configurations of the neutron-rich 29,30Na isotopes, obtained via Coulomb dissociation (CD) measurements. The invariant mass spectra of these nuclei have been obtained through measurement of the four-momenta of all decay products after Coulomb excitation of those nuclei on a 208Pb target at energies of 400-430 MeV/nucleon using the FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated inclusive Coulomb-dissociation cross-sections (CD) of 89 (7) mb and 167 (13) mb for one neutron removal from 29Na and 30Na, respectively, have been extracted up to an excitation energy of 10 MeV. The major part of one neutron removal, CD cross-sections of those nuclei populate the core, in its’ ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of 29Na(3/2+) and 30Na(2+) is the d-orbital with a small contribution from the s-orbital, which are coupled with the ground state of the core. One of the major components of the ground state configurations of these nuclei are 28Nags(1+) ⊗ νs,d and 29Nags(3/2+) ⊗ νs,d, respectively. The ground state spin and parity of these nuclei obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the s and d orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with shell model calculation using the MCSM suggests a lower limit of around 4.3 MeV of the sd − pf shell gap in 30Na.

The low-lying structure of 15C has been investigated via the neutron-removal 16C(d,t) reaction. Along with the known bound neutron sd-shell states, unbound p-shell hole states have been observed. The excitation energies and the deduced spectroscopic factors of the cross-shell states are an important measure of the [(p)−1(sd)2] neutron configurations in 15C. Our results show a very good agreement with shell-model calculations using the SFO-tls interaction for 15C. However, this same interaction predicted energies that were too low for the corresponding hole states in the N=9 isotone 17O and adjustment of the p-sd and sd-sd monopole terms was required to match the 17O energies. In addition, the excitation energies and spectroscopic factors have been compared to the first calculations of 15C with the ab initio self-consistent Green's function method employing the NNLOsat interaction. The results show the sensitivity to the size of the N=8 shell gap and highlight the need to go beyond the current truncation scheme.

The discovery of presolar grains in primitive meteorites has launched a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical Cl33 ( p,γ ) Ar34 reaction is expected to play a decisive role. As such, we have performed a detailed γ -ray spectroscopy study of Ar34 . Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in Ar34 , have been made for the first time. Uncertainties in the Cl33 ( p,γ ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ=0 resonance at Er=396.9 ( 13 ) keV dominates the entire rate for T=0.25–0.40 GK . Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected S 32/ S 33 abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain.

The single-particle properties of 29Mg have been investigated via a measurement of the 28Mg(d,p)29Mg reaction, in inverse kinematics, using the ISOLDE Solenoidal Spectrometer. The negative-parity intruder states from the f p shell have been identified and used to benchmark modern shell-model calculations. The systematic data on the single-particle centroids along the N = 17 isotones show good agreement with shell-model predictions in describing the observed trends from stability toward 25O. However, there is also evidence that the effect of the finite geometry of the nuclear potential is playing a role on the behavior of the p orbitals near the particle-emission threshold.

In recent decades, ?-ray spectroscopy has undergone a major technological leap forward, namely the technique of ?-ray tracking, and has attained a sensitivity that is two orders of magnitude larger than that provided by the former generation of Compton-shielded arrays. Indeed the gain is comparable with the achievements since the dawn of ?-ray spectroscopy. Such sensitivity can be further heightened by coupling ?-ray spectrometers to other detectors that record complementary reaction products such as light-charged particles for transfer reactions and scattered ions for Coulomb excitation measurements. Nucleon transfer reactions offer an excellent mean to probe the energies of shell model single-particle orbitals and to study migration in energy of these orbitals as we venture away from stability. Such measurements can also estimate the cross sections of processes relevant to stellar evolution and nucleosynthesis. The measurement of ? rays in coincidence with particles provides also information on the decay channel for unbound systems, which constitutes a useful input for astrophysics and nuclear structure near the drip-lines. Coulomb excitation studies make it possible to infer collective structure in nuclei and to extract deformation properties of, in particular, open-shell systems. Here, selected examples will be presented, highlighting the power of these types of experiments when ?-ray observation is included. The development of the experimental methods is reviewed, showing the results achieved before the advent of ?-ray tracking. Examples of more recent experiments that have successfully exploited ? - ray tracking with AGATA are then presented as showcases for the outstanding performance of the composite detection systems. The outlook for experiments using newly developed devices such as GRIT and other detectors such as SPIDER is described.

In this thesis, the radioactive beam (RIB) 25Na at 5 MeV/u with an intensity of up to 3 times 107 pps is exploited to study states in 26Na using a 0.5 mg/cm2 deuterated polyethylene (CD2) target via the highly selective (d,p gamma) transfer reaction. The reaction products are recorded by using both SHARC (the Silicon Highly-segmented Array for Reactions and Coulex) and TIGRESS (The TRIUMF-ISAC Gamma-Ray Escape-Suppressed Spectrometer). The SHARC array is installed at the ISAC-2 facility in TRIUMF (Canada) to study a variety of reactions, but single-particle transfer with a radioactive ion beam is the reaction mechanism of interest here. This experimental study was the first radioactive beam experiment making use of the TIGRESS/SHARC detector set-up in 2009. This work significantly extends an earlier analysis. The motivation of this work is to combine the information extracted from the particle and the gamma detection in 25Na(d,p gamma) 26Na reaction data to compare the experimentally observed results and the shell model predictions. A total of 24 states were studied, of which 10 had not been reported previously, and detailed new information was extracted for most of these. Properties measured and discussed include: (1) the observed gamma-ray decay branching ratios, (2) the observed spectroscopic factors (population strength) in the (d,p) reaction, (3) the observed angular momentum transfer in the (d,p) reaction, (4) a comparison between experimental and the predicted excitation energies from shell model calculations, (5) spin assignments based on the predicted reaction strengths and observed gamma-ray decay scheme, and (6) analogies with the experimentally observed gamma-decay properties of the isotone 28Al. An extra new feature of this work, for the important interpretation of similar future experiments, is a detailed study of the gamma-ray angular distributions and their dependence upon the scattered proton angles in (d,p).

The quenching of the N=20 shell gap in neutron-rich nuclei is investigated by studying the single-particle structure of 27Ne via neutron transfer using a 26Ne beam. Two low-lying negative-parity intruder states have been observed, the lowest of which is identified as Jπ=3/2−, confirming earlier speculations. A level identified as 7/2− is observed higher in energy than the 3/2−, contrary to the ordering at β-stability and at an energy significantly different from the predictions of previous shell-model calculations. The measured energies and deduced spectroscopic factors are well reproduced in full (0,1)-ℏω 0s-0p-0d-1s-0f-1p calculations in which there is a significant ad hoc reduction (∼0.7 MeV) in the N=20 shell gap.

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 occurence of ``exotic'' shapes in light N = Z α-like nuclei is investigated for 24Mg+12C and 32S+24Mg. Various approaches of superdeformed and hyperdeformed bands associated with quasimolecular resonant structures with low spin are presented. For both reactions, exclusive data were collected with the Binary Reaction Spectrometer in coincidence with EUROBALL IV installed at the VIVITRON Tandem facility of Strasbourg. Specific structures with large deformation were selectively populated in binary reactions and their associated γ-decays studied. The analysis of the binary and ternary reaction channels is discussed.

The 12C + 12C fusion reaction plays a critical role in the evolution of massive stars and also strongly impacts various explosive astrophysical scenarios. The presence of resonances in this reaction at energies around and below the Coulomb barrier makes it impossible to carry out a simple extrapolation down to the Gamow window—the energy regime relevant to carbon burning in massive stars. The 12C + 12C system forms a unique laboratory for challenging the contemporary picture of deep sub-barrier fusion (possible sub-barrier hindrance) and its interplay with nuclear structure (sub-barrier resonances). Here, we show that direct measurements of the 12C + 12C fusion cross section may be made into the Gamow window using an advanced particle-gamma coincidence technique. The sensitivity of this technique effectively removes ambiguities in existing measurements made with gamma ray or charged-particle detection alone. The present cross-section data span over 8 orders of magnitude and support the fusion-hindrance model at deep sub-barrier energies.

We present the design, prototype developments and test results of the new time-of-flight detector (ToFD) which is part of the R-3 B experimental setup at GSI and FAIR, Darmstadt, Germany. The ToFD detector is able to detect heavy-ion residues of all charges at relativistic energies with a relative energy precision sigma(Delta E)/Delta E of up to 1% and a time precision of up to 14 ps (sigma). Together with an elaborate particle-tracking system, the full identification of relativistic ions from hydrogen up to uranium in mass and nuclear charge is possible.

Proton capture on the excited isomeric state of ^{26}Al strongly influences the abundance of ^{26}Mg ejected in explosive astronomical events and, as such, plays a critical role in determining the initial content of radiogenic ^{26}Al in presolar grains. This reaction also affects the temperature range for thermal equilibrium between the ground and isomeric levels. We present a novel technique, which exploits the isospin symmetry of the nuclear force, to address the long-standing challenge of determining proton-capture rates on excited nuclear levels. Such a technique has in-built tests that strongly support its veracity and, for the first time, we have experimentally constrained the strengths of resonances that dominate the astrophysical ^{26m}Al(p,γ)^{27}Si reaction. These constraints demonstrate that the rate is at least a factor ∼8 lower than previously expected, indicating an increase in the stellar production of ^{26}Mg and a possible need to reinvestigate sensitivity studies involving the thermal equilibration of ^{26}Al.

Data have been obtained on exclusive single neutron knockout cross sections from 12Be to study its ground state structure. The cross sections for the production of 11Be in its ground state (1/2 +) and first excited state (0.32 MeV, 1/2 -) have previously been measured, indicating a strong (2s 1 2) 2 component to the 12Be ground state. In the present experiment, performed at the GANIL laboratory, cross sections for the first (0.32 MeV, 1/2 -) and second (1.78 MeV, 5/2 +, unbound) excited states in 11Be were measured, which gives information on the admixture of (1p 1 2) 2 and (1d 5 2) 2 components in the ground state of 12Be. A fragmentation beam of 12Be of ∼10000 pps (95% pure) was incident on a carbon target at 41 MeV/u. The beam particles were tracked onto the target, and their energies were measured event-by-event. The beam-like residues were measured in a position sensitive telescope mounted at zero degrees, and neutrons were measured in the DéMoN array. The 1/2 - state of 11Be was identified by measuring coincident 320 keV γ-rays, using four NaI detectors. Full kinematic reconstruction of unbound states in 11Be was performed using coincident neutrons and 10Be ions. Detailed simulations were performed in order to interpret the data, and spectroscopic factors were calculated, using preliminary single particle removal cross sections calculated using a Glauber model. © 2005 American Institute of Physics.

The astrophysical s-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding s-process nucleosynthesis is the neutron flux generated by the Ne-22(alpha, n)Mg-25 reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing Ne-22(alpha, gamma)Mg-26 reaction, is not well constrained in the important temperature regime from similar to 0.2-0.4 GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the Ne-22(Li-6, d)Mg-26 reaction in inverse kinematics, detecting the outgoing deuterons and Mg-25,Mg-26 recoils in coincidence. We have established a new n/gamma decay branching ratio of 1.14(26) for the key E-x = 11.32 MeV resonance in Mg-26, which results in a new (alpha, n) strength for this resonance of 42(11) mu eV when combined with the well-established (alpha, gamma) strength of this resonance. We have also determined new upper limits on the alpha partial widths of neutron-unbound resonances at E-x = 11.112, 11.163, 11.169, and 11.171 MeV. Monte-Carlo calculations of the stellar Ne-22(alpha, n)Mg-25 and Ne-22(alpha, gamma)Mg-26 rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from similar to 0.2-0.4 GK. (C) 2020 The Authors. Published by Elsevier B.V.

The 7Li(7Li, 11B*)t, 12C(7Li, 10B*)9Be and 7Li(7Li, 12B*)d reactions have been studied at 58 MeV in order to determine the relative strengths of the H + Be and α + Li decay of 10,11,12B. A study of the relative yields for the decay of a number of excited states in 10,11,12B*, obtained following the coincident detection of the H + Be and α + Li decay fragments, indicates that the α-decay channel dominates in all cases. © 2006 American Institute of Physics.

Background: Neutron-rich nuclei around neutron number N = 60 show a dramatic shape transition from spherical ground states to prolate deformation in Sr-98 and heavier nuclei. Purpose: The purpose of this study is to investigate the single-particle structure approaching the shape transitional region. Method: The level structures of neutron-rich Sr-93,Sr-94,Sr-95 were studied via the H-2(Sr-94,Sr-95,Sr-96, t) one-neutron stripping reactions at TRIUMF using a beam energy of 5.5 AMeV. gamma-rays emitted from excited states and recoiling charged particles were detected by using the TIGRESS and SHARC arrays, respectively. States were identified by gating on the excitation energy and, if possible, the coincident gamma radiation. Results: Triton angular distributions for the reactions populating states in ejectile nuclei Sr-93,Sr-94,Sr-95 were compared with distorted wave Born approximation calculations to assign and revise spin and parity quantum numbers and extract spectroscopic factors. The results were compared with shell-model calculations and the reverse (d, p) reactions and good agreement was obtained. Conclusions: The results for the H-2(Sr-94, t) Sr-93 and H-2(Sr-95, t) Sr-94 reactions are in good agreement with shell-model calculations. A two-level mixing analysis for the 0(+) states in Sr-94 suggest strong mixing of two shapes. For the H-2(Sr-96, t) Sr-95 reaction the agreement with the shell-model is less good. The configuration of the ground state of Sr-96 is already more complex than predicted, and therefore indications for the shape transition can already be observed before N = 60.

We have measured the cross section of the( 83)Rb(p, ? ) Sr-84 radiative capture reaction in inverse kinematics using a radioactive beam of Rb-83 at incident energies of 2.4 and 2.7A MeV. Prior to the radioactive beam measurement, the Kr-84(p, ? ) Rb-85 radiative capture reaction was measured in inverse kinematics using a stable beam of Kr-84 at an incident energy of 2.7A MeV. The effective relative kinetic energies of these measurements lie within the relevant energy window for the ? process in supernovae. The central values of the measured partial cross sections of both reactions were found to be 0.17-0.42 times the predictions of statistical model calculations. Assuming the predicted cross section at other energies is reduced by the same factor leads to a slightly higher calculated abundance of the p nucleus Sr-84, caused by the reduced rate of the Sr-84(? , p) Rb-83 reaction derived from the present measurement.

In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target has been used to produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified eventby- event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive silicon active stopper which allowed pixelated correlations between implants and their subsequent β-decay. Discrete γ-ray transitions emitted following decays from either metastable states or excited states populated following beta decay were identified using the 84 coaxial high-purity germanium (HPGe) detectors of the EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3)

The MUGAST-AGATA-VAMOS set-up at GANIL combines the MUGAST highly-segmented silicon array with the state-of-the-art AGATA array and the large acceptance VAMOS spectrometer. The mechanical and electronics integration copes with the constraints of maximum efficiency for each device, in particular γ-ray transparency for the silicon array. This complete set-up offers a unique opportunity to perform exclusive measurements of direct reactions with the radioactive beams from the SPIRAL1 facility. The performance of the set-up is described through its commissioning and two examples of transfer reactions measured during the campaign. High accuracy spectroscopy of the nuclei of interest, including cross-sections and angular distributions, is achieved through the triple-coincidence measurement. In addition, the correction from Doppler effect of the γ-ray energies is improved by the detection of the light particles and the use of two-body kinematics and a full rejection of the background contributions is obtained through the identification of heavy residues. Moreover, the system can handle high intensity beams (up to 108 pps). The particle identification based on the measurement of the time-of-flight between MUGAST and VAMOS and the reconstruction of the trajectories is investigated.

The 24 Mg + 12 C fusion reaction was used to perform a detailed γ-ray spectroscopy study of the astrophysically important nucleus 34 Ar. In particular, an experimental setup, coupling the advanced γ-ray tracking array GRETINA with the well-established Argonne fragment mass analyzer (FMA), was employed to obtain excitation energies and spin-parity assignments for excited states in 34 Ar, both above and below the proton separation energy. For the first time, an angular distribution analysis of in-beam γ rays from fusion-evaporation reactions, using a tracking array, has been performed and Coulomb energy differences of analog states in the T = 1, A = 34 mirror system, explored from 0 to 6 MeV. Furthermore, we present a comprehensive discussion of the astrophysical 33 Cl(p, γ) stellar reaction rate, together with implications for the identification of nova presolar grains from sulfur isotopic abundances.

The isovector and isoscalar components of neutron-proton pairing are investigated in the N=Z unstable nuclei of the fp-shell through the two-nucleon transfer reaction (p,3He) in inverse kinematics. The combination of particle and gamma-ray detection with radioactive beams of 56Ni and 52Fe, produced by fragmentation at the GANIL/LISE facility, made it possible to carry out this study for the first time in a closed and an open-shell nucleus in the fp-shell. The transfer cross-sections for ground-state to ground-state (J=0+, T=1) and to the first (J=1+, T=0) state were extracted for both cases together with the transfer cross-section ratios σ(0+,T=1)/σ(1+,T=0). They are compared with second-order distorted-wave born approximation (DWBA) calculations. The enhancement of the ground-state to ground-state pair transfer cross-section close to mid-shell, in 52Fe, points towards a superfluid phase in the isovector channel. For the “deuteron-like” transfer, very low cross-sections to the first (J=1+, T=0) state were observed both for 56Ni(p,3He) and 52Fe(p,3He) and are related to a strong hindrance of this channel due to spin-orbit effect. No evidence for an isoscalar deuteron-like condensate is observed.

The nature of the 1(-) and 2(-) excited states in Be-10 is studied using the Be-11(p, d) transfer reaction in inverse kinematics at 10A MeV at TRIUMF ISAC-II, in particular to assess whether either of them can be considered as an excited halo state. The angular distributions for both states are extracted using deuteron-gamma( )coincidences and analyzed using a transfer model taking into account one-step and two-step processes. A good fit of the angular distributions is obtained considering only the one-step process, whereby an inner p(3/2) neutron of Be-11 is removed, leaving the halo neutron intact. Higher-order processes however cannot be rejected. The small spectroscopic factors extracted suggest that the structure of both states is not uniquely halo-like, but rather display a more complex configuration mixing cluster and halo structures. Further insights are limited, as this experiment specifically probed the halo-like (but not cluster-like) Be-11 (1/2(+)) circle times (nu p(3/2))(-1) configuration in both states.

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 evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution. In this work, we investigate the Z = 6 spin-orbit shell gap towards the neutron dripline. To do so, we employed N-A(p,2p)CA-1 quasi-free scattering reactions to measure the proton component of the 2(1)(+) state of C-16,C-18,C-20. The experimental findings support the notion of a moderate reduction of the proton 1p(1/2) - 1p(3/2) spin-orbit splitting, at variance to recent claims for a prevalent Z = 6 magic number towards the neutron dripline. (C) 2020 The Authors. Published by Elsevier B.V.

Measurements of the 4He(7Be,α)7Be and 4He(7Be,p)10B reactions were performed using 7Be beam energies of 7.1 and 23 MeV and a helium-4 target, employing the thick target technique. Resonances were observed between E 11C)=8.6 to 13.8 MeV. An R-matrix analysis was performed to characterize the spins and partial widths. This analysis showed that the observed sequence of states was consistent with that found for 7Li + α resonant scattering populating resonances in 11B. A comparison of the proposed partial widths for decay with the Wigner limit indicates that several of the states are associated with cluster-like structures. © 2012 American Physical Society.

Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on 20,21N are reported. Relativistic 20,21N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the 19N(n, γ) 20N and 20N(n, γ) 21N excitation functions and thermonuclear reaction rates have been determined. The 19N(n, γ) 20N rate is up to a factor of 5 higher at T < 1 GK with respect to previous theoretical calculations, leading to a 10 % decrease in the predicted fluorine abundance.

Intermediate energy single-neutron removal from 31Mg has been employed to investigate the transition into the N = 20 island of inversion. Levels up to 5 MeV excitation energy in 30Mg were populated and spin-parity assignments were inferred from the corresponding longitudinal momentum distributions and γ -ray decay scheme. Comparison with eikonal-model calculations also permitted spectroscopic factors to be deduced. Surprisingly, the 0+ 2 level in 30Mg was found to have a strength much weaker than expected in the conventional picture of a predominantly 2p−2h intruder configuration having a large overlap with the deformed 31Mg ground state. In addition, negative parity levels were identified for the first time in 30Mg, one of which is located at low excitation energy. The results are discussed in the light of shell-model calculations employing two newly developed approaches with markedly different descriptions of the structure of 30Mg. It is concluded that the cross-shell effects in the region of the island of inversion at Z = 12 are considerably more complex than previously thought and that np−nh configurations play a major role in the structure of 30Mg.

In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of γ-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 108 n s−1cm−2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr3:(Ce) detectors from the FATIMA collaboration. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 × 105 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(Ce) detectors to analyze half-lives of excited levels in the pico- to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of 133Ba, 60Co and 152Eu as well as data from the reactions 27Al(n,γ)28Al and 35Cl(n,γ)36Cl in the energy range from 30 keV up to 10 MeV.

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process, β-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.

© Published under licence by IOP Publishing Ltd.An experimental technique for studying elastic scattering using a thick gas target is described, with a measurement of the α(24Ne,α) reaction used as an example. Advantages such as ease, detector efficiency, and the possibility of measuring the cross section at 180° in the centre-of-mass are discussed. It is shown that a resolution of tens of keV is practical at zero degrees, and that the dominant contribution to the resolution for large angles is angular straggling of the beam in the entrance window. The use of helium gas as the target allows direct measurement of a-cluster states.

Coulomb breakup of unstable neutron rich nuclei 29,30Na around the 'island of inversion' has been studied at energy around 434 MeV/nucleon and 409 MeV/nucleon respectively. Four momentum vectors of fragments, decay neutron from excited projectile and γ-rays emitted from excited fragments after Coulomb breakup are measured in coincidence. For these nuclei, the low-lying dipole strength above one neutron threshold can be explained by direct breakup model. The analysis for Coulomb breakup of 29,30Na shows that large amount of the cross section yields the 28Na, 29Na core in ground state. The predominant ground-state configuration of 29,30Na is found to be 28Na(g.s) νs1/2 and 29Na(g.s) νs1/2,respectively. © Owned by the authors, published by EDP Sciences, 2014.

The gamma-decay properties of 24Mg excited states are investigated in the inverse reaction 24Mg+12C at E(24Mg) = 130 MeV. At this energy the direct inelastic scattering populates a 24Mg* energy region where 12C+12C breakup resonances can occur. Very exclusive data were collected with the Binary Reaction Spectrometer (BRS) in coincidence with EUROBALL installed at the VIVITRON Tandem facility of the IReS at Strasbourg. The experimental detection system is decribed and preliminary results of binary reaction coincid data are presented.

Nucleon transfer experiments have in recent years begun to be exploited in the study of nuclei far from stability, using radioactive beams in inverse kinematics. New techniques are still being developed in order to perform these experiments. The present experiment is designed to study the odd-odd nucleus Na which has a high density of states and therefore requires gamma-ray detection to distinguish between them. The experiment employed an intense beam of up to 3×10 pps of Na at 5.0 MeV/nucleon from the ISAC-II facility at triumf. The new silicon array SHARC was used for the first time and was coupled to the segmented clover gamma-ray array TIGRESS. A novel thin plastic scintillator detector was employed at zero degrees to identify and reject reactions occurring on the carbon component of the (CD) target. The efficiency of the background rejection using this detector is described with respect to the proton and gamma-ray spectra from the (d,p) reaction. © Published under licence by IOP Publishing Ltd.

We discuss the use of one proton-removal reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics, with particular reference to the results of a GANIL experiment with a cocktail beam around 23Al at 50 MeV/nucleon. Momentum distributions of the core fragments, inclusive and in coincidence with gamma rays detected with EXOGAM, were measured. From them we determine mixing ratios in the structure of the ground states of the projectile nuclei and the asymptotic normalization of their wave functions. The method has the advantage that can be used for beams of low quality, such as cocktail beams, and intensities as low as a few pps. The proton breakup reactions provide information to determine astrophysical (p,γ) reaction rates that are outside the reach of other direct or indirect methods, or complementary information to the use of transfer reactions (the ANC method) which require radioactive beams of much better purity and intensity. Preliminary results on proton breakup of 24Si, 23Al, 22Mg and 21Na will be presented. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial- ShareAlikeLicence.

The nuclear matter and charge radii of the helium isotopes (A=4,6,8) are calculated by quantitative geometrical thermodynamics (QGT) taking as input the symmetry of the alpha-particle, the very weak binding (and hence halo nature) of the heavier helium isotopes, and a characteristic length scale given by the proton size. The results follow by considering each isotope in its ground state, with QGT representing each system as a maximum entropy configuration that conforms to the Holographic Principle. This allows key geometric parameters to be determined from the number of degrees of freedom available. QGT treats 6He as a 4He core plus a concentric neutron shell comprising a holomorphic pair of neutrons, and the 8He neutron halo is treated as a holomorphic pair of holomorphic pairs. Considering that the information content of each system allows a correlation angle of 2/3 between the holomorphic entities to be inferred, then the charge radii of the three isotopes can be calculated from the displacement of the 4He core from the centre of mass. The calculations for the charge and matter radii of 4,6,8He agree closely with observed values. Similar QGT calculation of the sizes of the self-conjugate A=4n nuclei {4He, 8Be, 12C, 16O, 20Ne, 24Mg, 28Si, 32S, 36Ar, 40Ca} also agree well with experiment.

The reduced transition probabilities B(E2; 0+ g.s. → 2+ 1 ) of the 46Ar and 44Ca nuclei were studied using the Coulomb excitation technique at intermediate energy at the LISE/GANIL facility. The in-flight γ rays, emitted after the Coulomb excitation of their first 2+ states, were detected in an array of 64 BaF2 crystals. The present B(E2 ↑) value for 44Ca, 475(36) e2fm4 , agrees well with the value of 495(35) e2fm4 obtained by averaging results of previous experiments. Consistent B(E2; 0+ g.s. → 2+ 1 ) values of 225(29) e2fm4 and 234(19) e2fm4 have been obtained for 46Ar from an absolute and a relative measurement, normalized to the 44Ca value. Both results agree with the ones obtained with the same experimental technique at the NSCL facility but are a factor of 2 smaller than the shell model predictions. The drop in B(E2; 0+ g.s. → 2+ 1 ) in the Ar chain at N = 28, confirmed in this experiment, shows that 46Ar is sensitive to the N = 28 shell closure.

A search has been made for the 6He+6He and alpha + 8He decay of the molecular rotational band in 12Be using the 10Be(14C,12Be*)12C reaction at 88.5 MeV. Although the alpha + 6He decay of 10Be was observed in the data set there is no evidence for the breakup of 12Be. The cross-section upper limits for the 10Be(14C,6He 6He)12C and 10Be(14C,alpha 8He)12C reactions are 50 and 300 nb respectively.

Motivated by the importance of P25 for the two-proton decay of S26 and for searches of the mirror analog of the island of inversion near N=16, we present the first predictions for the spectroscopy of the exotic isotope P25 obtained in the shell model, a potential model, and a microscopic-cluster model. All models predict P25 to be unbound, with an energy in the range 0.78-1.03 MeV, which favors previous mass systematics over more recent revisions. We show that P25 possesses a rich low-lying spectrum that should be accessible by experimental studies. All of the predicted states below 7 MeV, except one, are narrow. Many of them are built on the excited-core states of 24Si for which the Coulomb barrier is raised. For decays into the 24Si(g.s.)+p channel we determined the proton widths based on their link to the asymptotic normalization coefficients (ANCs) of their mirror analogs in 25Ne. We determine these ANCs from the analysis of the transfer reaction 24Ne(d,p)25Ne. The proton widths for decay into excited-state channels are obtained in model calculations. The only broad state is the intruder 3/2-, the mirror analog of which has been recently observed in 25Ne. The 25P(3/2-) energy is lower than that in 25Ne, suggesting that the island of inversion may persist on the proton-rich side. All excited states of P25 have at least two decay modes and are expected to populate variously the 21,2+ and 4+ states in 24Si, which then decay electromagnetically.

Ameasurement of the α(12C, α) 12Creaction has been performed using resonant scattering with a gas target. Beam energies of 46, 52, 56 and 63 MeV were used to populate resonances in the excitation energy range of 11.6–22.9 MeV in 16O. The angular distributions of the elastic scattering were measured at zero degrees, using an array of segmented silicon strip detectors with a minimum range of 0◦–30◦ in the centre-of-mass. The spins of 8 resonances between 14.1 and 18.5 MeV were obtained, confirming spin assignments made using elastic scattering in normal kinematics. An R-matrix analysis of the data was performed which indicates that the present understanding of 16O in this region is good, but not complete.

We measured 135 cross sections of residual nuclei produced in fragmentation reactions of C-12, N-14, and O-13-16,O-20,O-22 projectiles impinging on a carbon target at kinetic energies of near 400A MeV, most of them for the first time, with the R B-3/LAND setup at the GSI facility in Darmstadt (Germany). The use of this state-of-the-art experimental setup in combination with the inverse kinematics technique gave the full identification in atomic and mass numbers of fragmentation residues with a high precision. The cross sections of these residues were determined with uncertainties below 20% for most of the cases. These data are compared to other previous measurements with stable isotopes and are also used to benchmark different model calculations.

The ISOLDE Scientific Infrastructure at CERN offers a unique range of post-accelerated radioactive beams. The scientific program can be improved with the "Isolde Superconducting Recoil Separator" (ISRS), an innovative spectrometer able to deliver unprecedented (A, Z) resolution. In this paper we present an overview of the physics and ongoing technical developments.

The 25 Al(p, γ) reaction has long been highlighted as a possible means to bypass the production of 26 Al cosmic γ rays in classical nova explosions. However, uncertainties in the properties of key resonant states in 26 Si have hindered our ability to accurately model the influence of this reaction in such environments. We report on a detailed γ-ray spectroscopy study of 26 Si and present evidence for the existence of a new, likely ℓ = 1, resonance in the 25 Al + p system at Er = 153.9(15) keV. This state is now expected to provide the dominant contribution to the 25 Al(p, γ) stellar reaction rate over the temperature range, T ∼ 0.1 − 0.2 GK. Despite a significant increase in the rate at low temperatures, we find that the final ejected abundance of 26 Al from classical novae remains largely unaffected even if the reaction rate is artificially increased by a factor of 10. Based on new, Galactic chemical evolution calculations, we estimate that the maximum contribution of novae to the observed Galactic abundance of 26 Al is ∼0.2 M⊙. Finally, we briefly highlight the important role that Super-AGB stars may play in the production of 26 Al.

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.

The levels in 26Na with single particle character have been observed for the first time using the d(25Na, pγ ) reaction at 5 MeV/nucleon. The measured excitation energies and the deduced spectroscopic factors are in good overall agreement with (0+1)ħω(0+1)ħω shell model calculations performed in a complete spsdfpspsdfp basis and incorporating a reduction in the N=20 gapN=20 gap. Notably, the 1p3/21p3/2 neutron configuration was found to play an enhanced role in the structure of the low-lying negative parity states in 26Na, compared to the isotone 28Al. Thus, the lowering of the 1p3/21p3/2 orbital relative to the 0f7/20f7/2 occurring in the neighbouring Z=10Z=10 and 12 nuclei – 25,27Ne and 27,29Mg – is seen also to occur at Z=11Z=11 and further strengthens the constraints on the modelling of the transition into the island of inversion.

We have recently successfully demonstrated a new technique for production and study of many of the most exotic neutron-rich nuclei at moderate spins. LICORNE, a newly developed directional inverse-kinematic fast neutron source at the IPN Orsay, was coupled to the MINIBALL high resolution -ray spectrometer to study nuclei the furthest from stability using the 238U(n; f) reaction. This reaction and 232Th(n; f) are the most neutron-rich fission production mechanisms achievable and can be used to simultaneously populate hundreds of neutron-rich nuclei up to spins of 16 ~. High selectivity in the experiment was achieved via triple -ray coincidences and the use of a 400 ns period pulsed neutron beam, a technique which is unavailable to other population mechanisms such as 235U(nth; f) and 252Cf(SF). The pulsing allows time correlations to be exploited to separate delayed rays from isomeric states in the hundreds of nuclei produced, which are then used to cleanly select a particular nucleus and its exotic binary partners. In the recent experiment, several physics cases are simultaneously addressed such as shape coexistence, the evolution of shell closures far from stability, and the spectroscopy of nuclei in the r-process path near N = 82. Preliminary physics results on anomalies in the 238U(n; f) fission yields and the structure of the 138Te and 100Sr nuclei will soon be published. A future project, -ball, to couple LICORNE with a hybrid escape-suppressed spectrometer to refine further the technique and achieve a large increase in the observational limit is discussed.

The first investigation of the single-particle structure of the bound states of 17C, via the C transfer reaction, has been undertaken. The measured angular distributions confirm the spin-parity assignments of and for the excited states located at 217 and 335 keV, respectively. The spectroscopic factors deduced for these states exhibit a marked single-particle character, in agreement with shell model and particle-core model calculations, and combined with their near degeneracy in energy provide clear evidence for the absence of the sub-shell closure. The very small spectroscopic factor found for the ground state is consistent with theoretical predictions and indicates that the strength is carried by unbound states. With a dominant valence neutron configuration and a very low separation energy, the excited state is a one-neutron halo candidate.

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.

In atomic nuclei, the spin-orbit interaction originates from the coupling of the orbital motion of a nucleon with its intrinsic spin. Recent experimental and theoretical works have suggested a weakening of the spin-orbit interaction in neutron-rich nuclei far from stability. To study this phenomenon, we have investigated the spin-orbit energy splittings of single-hole and single-particle valence neutron orbits of 132Sn. The spectroscopic strength of single-hole states in 131Sn was determined from the measured differential cross sections of the tritons from the neutron-removing 132Sn(d,t)131Sn reaction, which was studied in inverse kinematics at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. The spectroscopic factors of the lowest 3=2+, 1=2+ and 5=2+states were found to be (2 j+1), confirming the robust N = 82 shell closure at 132Sn. We compared the spin-orbit splitting of neutron single-hole states in 131Sn to those of single-particle states in 133Sn determined in a recent measurement of the 132Sn(d,p)133Sn reaction. We found a significant reduction of the energy splitting of the weakly bound 3p orbits compared to the well-bound 2d orbits, and that all the observed energy splittings can be reproduced remarkably well by calculations using a onebody spin-orbit interaction and a Woods-Saxon potential of standard radius and diffuseness. The observed reduction of spin-orbit splitting can be explained by the extended radial wavefunctions of the weakly bound orbits, without invoking a weakening of the spin-orbit strength.

The low-lying structure of 13 Be has remained an enigma for decades. Despite numerous experimental and theoretical studies, large inconsistencies remain. Being both unbound and one neutron away from 14 Be , the heaviest bound beryllium nucleus, 13 Be is difficult to study through simple reactions with weak radioactive-ion beams or more complex reactions with stable-ion beams. Here, we present the results of a study using the 12 Be ⁢(𝑑,𝑝)⁢ 13 Be reaction in inverse kinematics using a 9.5 MeV per nucleon 12 Be beam from the ISAC-II facility. The solid deuteron target of IRIS was used to achieve an increased areal thickness compared to conventional deuterated polyethylene targets. The 𝑄-value spectrum below −4.4 MeV was analyzed using a Bayesian method with geant4 simulations. A three-point angular distribution with the same 𝑄-value gate was fit with a mixture of 𝑠- and 𝑝-wave, 𝑠- and 𝑑-wave, or pure 𝑝-wave transfer. The 𝑄-value spectrum was also compared with geant simulations obtained using the energies and widths of states reported in four previous works. It was found that our results are incompatible with works that revealed a wide 5/2+ resonance but shows better agreement with ones that reported a narrower width.

We have performed the first direct measurement of the 38Kðp; γÞ39Ca reaction using a beam of radioactive 38K. A proposed l ¼ 0 resonance in the 38K þ p system has been identified at 679(2) keV with an associated strength of 120 þ50 −30 meV. Upper limits of 1.16 (3.5) and 8.6 (26) meV at the 68% (95%) confidence level were also established for two further expected l ¼ 0 resonances at 386 and 515 keV, respectively. The present results have reduced uncertainties in the 38Kðp; γÞ39Ca reaction rate at temperatures of 0.4 GK by more than 2 orders of magnitude and indicate that Ar and Ca may be ejected in observable quantities by oxygen-neon novae. However, based on the newly evaluated rate, the 38Kðp; γÞ39Ca path is unlikely to be responsible for the production of Ar and Ca in significantly enhanced quantities relative to solar abundances.

The astrophysical s-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding s-process nucleosynthesis is the neutron flux generated by the 22Ne(; n)25Mg reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing 22Ne(;)26Mg reaction, is not well constrained in the important temperature regime from 0:2–0:4 GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the 22Ne(6Li; d)26Mg reaction in inverse kinematics, detecting the outgoing deuterons and 25;26Mg recoils in coincidence. We have established a new n= decay branching ratio of 1:14(26) for the key Ex = 11:32 MeV resonance in 26Mg, which results in a new (; n) strength for this resonance of 42(11) eV when combined with the well-established (; ) strength of this resonance. We have also determined new upper limits on the partial widths of neutron-unbound resonances at Ex = 11:112; 11:163, 11:169, and 11:171 MeV. Monte-Carlo calculations of the stellar 22Ne(; n)25Mg and 22Ne(; )26Mg rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from 0:2–0:4 GK.

Fast-neutron-induced fission of 238U at an energy just above the fission threshold is studied with a novel technique which involves the coupling of a high-efficiency γ-ray spectrometer (MINIBALL) to an inverse-kinematics neutron source (LICORNE) to extract charge yields of fission fragments via γ−γ coincidence spectroscopy. Experimental data and fission models are compared and found to be in reasonable agreement for many nuclei; however, significant discrepancies of up to 600% are observed, particularly for isotopes of Sn and Mo. This indicates that these models significantly overestimate the standard 1 fission mode and suggests that spherical shell effects in the nascent fission fragments are less important for low-energy fast-neutron-induced fission than for thermal neutron-induced fission. This has consequences for understanding and modeling the fission process, for experimental nuclear structure studies of the most neutron-rich nuclei, for future energy applications (e.g., Generation IV reactors which use fast-neutron spectra), and for the reactor antineutrino anomaly.

We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165;167Tb100;102. The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm 9Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the s regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165Tb and 167Tb and interpreted as arising from hindered E1 decay from the 7 2 [523] single quasi-proton Nilsson configuration to rotational states built on the 3 2 [411] single quasi-proton ground state. These data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the 170Dy doubly-midshell nucleus is approached.

The cluster structure of C-12 is explored and recent measurements of proton inelastic scattering, suggesting a 2(+) state close to 9.6 MeV are presented. Resonant scattering studies of Be-10+He-4 used to populate resonances in C-14 are briefly discussed.

States in 26Na were populated in the (d, pγ) reaction, induced by bombarding deuterium target nuclei with an intense reaccelerated beam of 25Na ions from the ISAC2 accelerator at TRIUMF. Gamma-rays were recorded in coincidence with protons and used to extract differential cross sections for 21 states up to the neutron decay threshold of 5 MeV. Results for levels below 3 MeV are discussed in detail and compared with shell model calculations and with previous work. The angular distributions of decay gamma-rays were measured for individual states and are compared to theoretically calculated distributions, highlighting some issues for future work.

BlueSTEAl, the Blue (aluminum chamber of) Silicon TElescope Arrays for light nuclei,has been developed to study direct reactions in inverse kinematics, as well as scattering and breakup reactions using radioactive ion beams. It is a detector system consisting of a pair of annular silicon detector arrays and a zero-degree phoswich plastic scintillator. For typical binary reaction studies in inverse kinematics, light ions are detected by the Si array in coincidence with heavy recoils detected by the phoswich placed at the focal-plane of a zero-degree magnetic spectrometer. The Si array can also be used to detect light nuclei such as berylium and carbon with clear isotope separation, while the phoswich can also be placed at zero degrees without a spectrometer and used as a high-efficiency beam counting monitor with particle identification capability at the rate of up to 5*10^4 particles per second. This paper reports on the capabilities of BlueSTEAl as determined by recent experiments performed at the Texas A&M Cyclotron Institute. The device is also anticipated to be used in future experiments at other radioactive ion beam facilities.

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.

Background: Classical novae are cataclysmic nuclear explosions occurring when a white dwarf in a binary system accretes hydrogen-rich material from its companion star. Novae are partially responsible for the galactic synthesis of a variety of nuclides up to the calcium ( A ∼ 40 ) region of the nuclear chart. Although the structure and dynamics of novae are thought to be relatively well understood, the predicted abundances of elements near the nucleosynthesis endpoint, in particular Ar and Ca, appear to sometimes be in disagreement with astronomical observations of the spectra of nova ejecta. Purpose: One possible source of the discrepancies between model predictions and astronomical observations is nuclear reaction data. Most reaction rates near the nova endpoint are estimated only from statistical model calculations, which carry large uncertainties. For certain key reactions, these rate uncertainties translate into large uncertainties in nucleosynthesis predictions. In particular, the 38 K ( p , γ ) 39 Ca reaction has been identified as having a significant influence on Ar, K, and Ca production. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate ℓ = 0 resonances within the Gamow window for nova burning, at 386 ± 10 keV, 515 ± 10 keV, and 689 ± 10 keV. Method: The experiment was performed in inverse kinematics using a beam of unstable 38 K impinged on a windowless hydrogen gas target. The 39 Ca recoils and prompt γ rays from 38 K ( p , γ ) 39 Ca reactions were detected in coincidence using a recoil mass separator and a bismuth-germanate scintillator array, respectively. Results: For the 689 keV resonance, we observed a clear recoil- γ coincidence signal and extracted resonance strength and energy values of 120 + 50 − 30 ( stat . ) + 20 − 60 ( sys . ) meV and 679 + 2 − 1 ( stat . ) ± 1 ( sys . ) keV , respectively. We also performed a singles analysis of the recoil data alone, extracting a resonance strength of 120 ± 20 ( stat . ) ± 15 ( sys . ) meV, consistent with the coincidence result. For the 386 keV and 515 keV resonances, we extract 90 % confidence level upper limits of 2.54 meV and 18.4 meV, respectively. Conclusions: We have established a new recommended 38 K ( p , γ ) 39 Ca rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of ∼ 250 . Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on Ar, K, and Ca synthesis to factors of 15 or less in all cases.

The kinematically complete measurements of the 7Li( 9Be,ααt)5He reaction at Ebeam = 55 and 70 MeV have been performed and the reconstructed 11B excitation energy spectra were compared with the 7Li(9Be, α7Li)5He results obtained at the same beam energies. Evidence was found for the t+8Be(g.s.) decay of the 11B excited states at 13.1 and 14.4 MeV, the α+7Li*(4.652 MeV) decay of the states at 14.4 and 17.5 MeV and for the t+ 8Be*(3.03 MeV) decay of the 17.5 MeV state in 11B. A study of the relative yields for the decay of the 14.4 MeV state indicates that significant part of α-decay strength goes into the 2α+t three-body decay channel. © 2006 American Institute of Physics.

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.

Background: Models describing nuclear fragmentation and fragmentation-fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool to reach the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes. Method: We have measured projectile fragments from 10,12-18C and 10-15B isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent dataset. We compare our data to model calculations. Results: One-proton removal cross sections with different final neutron numbers (1pxn) for relativistic 10,12-18C and 10-15B isotopes impinging on a carbon target. Comparing model calculations to the data, we find that EPAX is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease ABRABLA07 describes the data surprisingly well. Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data have allowed for a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.

Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R3B=LAND setup with incident beam energies in the range of 300–450 MeV=u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy onenucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type AOðp; 2pÞA−1N have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry.

We studied α cluster states in 26Mg via the 22Ne(6Li,dγ)26Mg reaction in inverse kinematics at an energy of 7 MeV/nucleon. States between Ex = 4–14 MeV in 26Mg were populated and relative α spectroscopic factors were determined. Some of these states correspond to resonances in the Gamow window of the 22Ne(α,n)25Mg reaction, which is one of the main neutron sources in the astrophysical s-process. Using our new 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg reaction rates, we performed new s-process calculations for massive stars and asymptotic giant branch stars and compared the resulting abundances with the abundances obtained using other 22Ne+α rates from the literature. We observe an impact on the s-process abundances up to a factor of three for intermediate-mass AGB stars and up to a factor of ten for massive stars. Additionally, states in 25Mg at Ex < 7.5 MeV are identified via the 22Ne(6Li,t)25Mg reaction for the first time. We present the (6Li, t) spectroscopic factors of these states and note similarities to the (d,p) reaction in terms of reaction selectivity.

We present new experimental measurements of resonance strengths in the astrophysical 23Al(p,γ)24Si reaction, constraining the pathway of nucleosynthesis beyond 22Mg in X-ray burster scenarios. Specifically, we have performed the first measurement of the (d,p) reaction using a radioactive beam of 23Ne to explore levels in 24Ne, the mirror analog of 24Si. Four strong single-particle states were observed and corresponding neutron spectroscopic factors were extracted with a precision of ∼20%. Using these spectroscopic factors, together with mirror state identifications, we have reduced uncertainties in the strength of the key ℓ = 0 resonance at Er = 157 keV, in the astrophysical 23Al(p,γ) reaction, by a factor of 4. Our results show that the 22Mg(p,γ)23Al(p,γ) pathway dominates over the competing 22Mg(α,p) reaction in all but the most energetic X-ray burster events (T>0.85 GK), significantly affecting energy production and the preservation of hydrogen fuel.

With the R3B-LAND setup at GSI we have measured exclusive relative-energy spectra of the Coulomb dissociation of 18C at a projectile energy around 425 AMeV on a lead target, which are needed to determine the radiative neutron-capture cross sections of 17C into the ground state of 18C. Those data have been used to constrain theoretical calculations for transitions populating excited states in 18C. This allowed to derive the astrophysical cross section n accounting for the thermal population of 17C target states in astrophysical scenarios. The experimentally veri ed capture rate is signi cantly lower than those of previously obtained Hauser-Feshbach estimations at temperatures T9 1 GK. Network simulations with updated neutron-capture rates and hydrodynamics according to the neutrino-driven wind model as well as the neutron-star merger scenario reveal no pronounced in uence of neutron capture of 17C on the production of second- and third-peak elements in contrast to earlier sensitivity studies.

The reduced transition probability B(E2: 3/2→7/2 ) has been measured in S using Coulomb excitation at intermediate energy. The nucleus of interest was produced by fragmentation of a Ca beam at GANIL. The reaction products were separated in the LISE spectrometer. After Coulomb-excitation of S in a Pb target, the γ rays emitted inflight were detected by 64 BaF detectors of the Chteau de Cristal array. The preliminary value deduced for the reduced transition probability B(E2: 3/2 →7/2 ) is in agreement with the predictions of the shell model calculations and supports a prolate-spherical shape coexistence in the S nucleus.

The low-lying structure of ¹⁵C has been investigated via the neutron-removal ¹⁶C(d,t) reaction. Along with bound neutron sd-shell hole states, unbound p-shell hole states have been firmly confirmed. The excitation energies and the deduced spectroscopic factors of the cross-shell states are an important measure of the [(p)−1(sd)2] neutron configurations in ¹⁵C. Our results show a very good agreement with shell-model calculations using the SFO-tls interaction for ¹⁵C. However, a modification of the p-sd and sd-sd monopole terms was applied in order to reproduce the N=9 isotone ¹⁷O. In addition, the excitation energies and spectroscopic factors have been compared to the first calculations of ¹⁵C with the ab initio self-consistent Green's function method employing the NNLOsat interaction. The results show the sensitivity to the size of the N=8 shell gap and highlight the need of going beyond the current truncation scheme in the theory.

A general experimental technique for high resolution studies of nucleon transfer reactions using radioactive beams is briefly described, together with the first new physics results that have been obtained with the new TIARA array. These first results from TIARA are for the reaction 24Ne(d,p)25Ne, studied in inverse kinematics with a pure radioactive beam of 100,000 pps from the SPIRAL facility at GANIL. The reaction probes the energies of neutron orbitals relevant to very neutron rich nuclei in this mass region and the results highlight the emergence of the N=16 magic number for neutrons and the associated disappearance of the N=20 neutron magic number for the very neutron rich neon isotopes.

The nuclei below lead but with more than 126 neutrons are crucial to an understanding of the astrophysical r-process in producing nuclei heavier than A ~ 190. Despite their importance, the structure and properties of these nuclei remain experimentally untested as they are difficult to produce in nuclear reactions with stable beams. In a first exploration of the shell structure of this region, neutron excitations in 207Hg have been probed using the neutron-adding (d,p) reaction in inverse kinematics. The radioactive beam of 206Hg was delivered to the new ISOLDE Solenoidal Spectrometer at an energy above the Coulomb barrier. The spectroscopy of 207Hg marks a first step in improving our understanding of the relevant structural properties of nuclei involved in a key part of the path of the r-process.

Measurements of the 4He(7Be,α)7Be and 4He(7Be,p)10B reactions were performed using 7Be beam energies of 7.1 and 23 MeV and a helium-4 target, employing the thick target technique. Resonances were observed between Ex(11C)=8.6 to 13.8 MeV. An R-matrix analysis was performed to characterize the spins and partial widths. This analysis showed that the observed sequence of states was consistent with that found for 7Li + α resonant scattering populating resonances in 11B. A comparison of the proposed partial widths for decay with the Wigner limit indicates that several of the states are associated with cluster-like structures.

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.

We have performed a direct measurement of the 19Ne(p,γ)20Na reaction in inverse kinematics using a beam of radioactive 19Ne. The key astrophysical resonance in the 19Ne+p system has been definitely measured for the first time at Ec.m.=456+5−2  keV with an associated strength of 17+7−5  meV. The present results are in agreement with resonance strength upper limits set by previous direct measurements, as well as resonance energies inferred from precision (3He, t) charge exchange reactions. However, both the energy and strength of the 456 keV resonance disagree with a recent indirect study of the 19Ne(d, n)20Na reaction. In particular, the new 19Ne(p,γ)20Na reaction rate is found to be factors of ∼8 and ∼5 lower than the most recent evaluation over the temperature range of oxygen-neon novae and astrophysical x-ray bursts, respectively. Nevertheless, we find that the 19Ne(p,γ)20Na reaction is likely to proceed fast enough to significantly reduce the flux of 19F in nova ejecta and does not create a bottleneck in the breakout from the hot CNO cycles into the rp process.

The astrophysical 25Al(p,γ) 26Si reaction represents one of the key remaining uncertainties in accurately modeling the abundance of radiogenic 26Al ejected from classical novae. Specifically, the strengths of key proton-unbound resonances in 26Si, that govern the rate of the 25Al(p,γ) reaction under explosive astrophysical conditions, remain unsettled. Here, we present a detailed spectroscopy study of the 26Si mirror nucleus 26Mg. We have measured the lifetime of the 3+, 6.125-MeV state in 26Mg to be 19(3) fs and provide compelling evidence for the existence of a 1– state in the T = 1, A = 26 system, indicating a previously unaccounted for ℓ = 1 resonance in the 25Al(p,γ) reaction. Using the presently measured lifetime, together with the assumption that the likely 1– state corresponds to a resonance in the 25Al + p system at 435.7(53) keV, we find considerable differences in the 25Al(p,γ) reaction rate compared to previous works. Furthermore, based on current nova models, we estimate that classical novae may be responsible for up to ≈ 15% of the observed galactic abundance of 26Al.

We have performed the first direct measurement of the Rb-83(p, gamma) radiative capture reaction cross section in inverse kinematics using a radioactive beam of Rb-83 at incident energies of 2.4 and 2.7A MeV. The measured cross section at an effective relative kinetic energy of E-cm = 2.393 MeV, which lies within the relevant energy window for core collapse supernovae, is smaller than the prediction of statistical model calculations. This leads to the abundance of Sr-84 produced in the astrophysical p process being higher than previously calculated. Moreover, the discrepancy of the present data with theoretical predictions indicates that further experimental investigation of p-process reactions involving unstable projectiles is clearly warranted.

An island of isomers have recently been observed on both sides of the N=40 shell below the Ni isotopes. Isomeric states in the 65Fe and 67Fe allow the knowledge of the single particle structure around the νg 9/2 shell. Moreover, the excitation energy of the first 2+ and 4+ states in the 68Fe have been established by β-γ correlation. The evolution of the structure of the Fe isotopes going far away from the valley of stability is, for the first time, given for N>40. © 2006 American Institute of Physics.

The island of inversion for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modeling of shell evolution with isospin. In this context, the structure of the transitional nucleus ²⁹Mg is critical. The first quantitative measurements of the single-particle structure of ²⁹Mg are reported, using data from the d(²⁸Mg, p γ)²⁹Mg reaction. Two key states carrying significant ℓ=3 (f-wave) strength were identified at 2.40±0.10 (Jπ=5/2¯) and 4.28±0.04 MeV (7/2¯). New state-of-the-art shell-model calculations have been performed and the predictions are compared in detail with the experimental results. While the two lowest 7/2¯ levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2¯ and 5/2¯ levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell-model calculations.