Approaching the precursor nuclei of the third r-process peak with RIBs

The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary $^{238}$U beam at GSI we were able to measure such properties for several neutron-rich nuclei from $^{208}$Hg to $^{218}$Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the beta-decay rates and with beta-delayed neutron emission is illustrated on the basis of $r$-process network calculations. In order to obtain a reasonable reproduction of the third $r$-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, commonly used in $r$-process model calculations. Further measurements around $N\sim126$ are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic $r$-process abundance calculations.The rapid neutron nucleosynthesis process involves an enormous amount of very exotic neutron-rich nuclei, which represent a theoretical and experimental challenge. Two of the main decay properties that affect the final abundance distribution the most are half-lives and neutron branching ratios. Using fragmentation of a primary 238U beam at GSI we were able to measure such properties for several neutron-rich nuclei from 208Hg to 218Pb. This contribution provides a short update on the status of the data analysis of this experiment, together with a compilation of the latest results published in this mass region, both experimental and theoretical. The impact of the uncertainties connected with the beta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to obtain a reasonable reproduction of the third r-process peak, it is expected that both half-lives and neutron branching ratios are substantially smaller, than those based on FRDM+QRPA, commonly used in r-process model calculations. Further measurements around N ~ 126 are required for a reliable modelling of the underlying nuclear structure, and for performing more realistic r-process abundance calculations

Gamma-ray spectroscopy approaching the limits of existence of atomic nuclei : a study of the excited states of 168Pt and 169Pt

Excited states in the N=90 and N=91 Pt nuclei have been investigated using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. These nuclei were populated via the reactions Mo92(Kr78,2n) and Mo94(Kr78,3n) at 335 and 348 MeV, respectively. The recoil-decay tagging technique has been used to correlate prompt γ radiation with the characteristic α decays of Pt168 and Pt169. A γ-γ analysis has allowed a level scheme for Pt168 to be reported for the first time and the level scheme for Pt169 to be extended. The excitation energies of the proposed positive-parity yrast states of Pt168 are compared with calculations based on the interacting boson model and found to be in excellent agreement. These data show a continuation of the trend toward vibrational nuclei as the N=82 shell gap is approached. In addition, new excited states constituting two decay paths have been discovered in Pt169

Competing quasiparticle configurations in W-163

Excited states in the neutron-deficient nuclide W163 were investigated using the Cd106(Ni60,2pn)W163 reaction at a beam energy of 270 MeV. The level scheme for W163 was extended significantly with the observation of five new band structures. The yrast band based on a 13/2+ isomeric state is extended up to (57/2+). Two band structures were established on the 7/2− ground state. Quasiparticle configuration assignments for the new band structures were made on the basis of cranked Woods-Saxon shell-model calculations. The results reported in this article suggest that the negative-parity ν(f7/2,h9/2) orbitals are responsible for the first rotational alignment in the yrast band

Total absorption γ-ray spectroscopy of beta delayed neutron emitters

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