Dr Katarzyna Hadynska-Klek

The transitional nucleus 131Xe is investigated after multinucleon transfer (MNT) in the 136Xe+208Pb and 136Xe+238U reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy and as an elusive reaction product in the fusion-evaporation reaction 124Sn(11B,p3n) 131Xe employing the HORUS ³-ray array coupled to a double-sided silicon strip detector (DSSSD) at the University of Cologne, Germany. The level scheme of 131Xe is extended to 5 MeV. A pronounced backbending is observed at ~É H 0.4 MeV along the negative-parity one-quasiparticle ½h11/2(± = ?1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations (LSSM) employing the PQM130, SN100PN, GCN50:82, SN100-KTH and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in 129?132Xe provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell closure. Proton occupancy in the À 0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon.

Fifty-five inclusive single nucleon removal cross sections from medium mass neutron-rich nuclei impinging on a hydrogen target at ý 250 MeV/nucleon were measured at the RIKEN Radioactive Isotope Beam Factory. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons compared to odd-proton number projectiles for a given neutron separation energy. Neutron removal cross sections display no even-odd splitting contrary to nuclear cascade model predictions. Both effects are understood through simple considerations of neutron separation energies and bound state level densities originating in pairing correlations in the daughter nuclei. These conclusions are supported by comparison with semi-microscopic model predictions,highlighting the enhanced role of low-lying level densities in nucleon removal cross sections from loosely-bound nuclei.

The reaction of a pulsed ¹⁸O beam on a ¹⁶⁴Dy target was studied in the first experiment with the NuBall array at the IPN Orsay, France. Excited state half-lives were measured using the fast timing method with 20 LaBr3(Ce) detectors. The timing characteristics of the fully digital acquisition system is briefly discussed. A value for the previously unknown half-life of the first excited 4⁺ state in ¹⁷⁸W is presented.

We report on the first measurement of the half-lives of and four-quasiparticle states in the even-even nucleus ¹⁷⁸W. The sub-nanosecond half-lives were measured by applying the centroid shift method to data taken with LaBr₃(Ce) scintillator detectors of the NuBall array at the ALTO facility in Orsay, France. The half-lives of these states only became experimentally accessible by the combination of several experimental techniques - scintillator fast timing, isomer spectroscopy with a pulsed beam, and the event-by-event calorimetry information provided by the NuBall array. The measured half-lives are and for the and states, respectively. The decay transitions include weakly hindered E1 and E2 branches directly to the ground-state band, bypassing the two-quasiparticle states. This is the first such observation for an E1 transition. The interpretation of the small hindrance hinges on mixing between the ground-state band and the t-band.