S. Pietri

First Measurement of Several β-Delayed Neutron Emitting Isotopes Beyond N=126

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

First results with the rising active stopper

This paper outlines some of the physics opportunities available with the GSI RISING active stopper and presents preliminary results from an experiment aimed at performing beta-delayed gamma-ray spectroscopic studies in heavy-neutron-rich nuclei produced following the projectile fragmentation of a 1 GeV per nucleon 208Pb primary beam. The energy response of the silicon active stopping detector for both heavy secondary fragments and beta-particles is demonstrated and preliminary results on the decays of neutron-rich Tantalum (Ta) to Tungsten (W) isotopes are presented as examples of the potential of this technique to allow new structural studies in hitherto experimentally unreachable heavy, neutron-rich nuclei. The resulting spectral information inferred from excited states in the tungsten daughter nuclei are compared with results from axially symmetric Hartree–Fock calculations of the nuclear shape and suggest a change in ground state structure for the N = 116 isotone 190W compared to the lighter isotopes of this element.

Electron Screening Effects on a-decay

An open problem in Nuclear Astrophysics concerns the understanding of electron‐screening effects on nuclear reaction rates at stellar energies. In this framework, we have proposed to investigate the influence of the electron cloud on α‐decay by measuring Q‐values and α‐decay half‐lives of fully stripped, H‐like and He‐like ions. These kinds of measurements have been feasible just recently for highly‐charged radioactive nuclides by fragmentation of 238U at relativistic energies at the FRS‐ESR facility at GSI. In this way it is possible to produce, efficiently separate and store highly‐charged α‐emitters. Candidates for the proposed investigation were carefully selected and will be studied by using the Schottky Mass Spectroscopy technique. In order to establish a solid reference data set, lifetimes and Qα‐value measurements of the corresponding neutrals have been performed directly at the FRS, by implanting the separated ions into an active Silicon stopper.

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 nmain 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. nThe impact of the uncertainties connected with the eta-decay rates and with beta-delayed neutron emission is illustrated on the basis of r-process network calculations. In order to nobtain 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, ncommonly 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.

Exotic nuclear studies around and below A = 100

A RISING experiment with an aim to study exotic Cd nuclei was carried out at GSI‐FRS facility. Some preliminary results from this experiment are presented here. In particular, the β decay of 96Cd to 96Ag revealed the existence of a high spin isomer predicted a few decades ago. In this context, the structures of both these nuclei are discussed. Shell model calculations using the Gross‐Frenkel interaction are used to interpret the results.

Nuclear Structure Addressed At GSI/RISING

Nuclear structure spectroscopy studies at GSI recently gained increased momentum within a broad international community with the installation of the Rare Isotopes Spectroscopic INvestigation at GSI (RISING) project. A wide range of physical phenomena has been addressed by high-resolution in-beam gamma-ray spectroscopy experiments with radioactive beams. Relativistic radioactive beams are implanted and their subsequent. and beta decay is investigated. Within this stopped beam campaign germanium detectors were arranged in a close geometry around the passive stopper or an array of DSSSD detectors. The exceptionally high gamma-ray efficiency of that configuration made it possible to identify decays of excited or ground states of nuclei which have not been observed before. The results discussed here include the astrophysically relevant shell structure of N=82 isotones, N=Z nuclei around Ni-54, and proton drip-line nuclei below Sn-100. The experimental data are compared to the results of large scale shell-model calculations using various sets of realistic residual two-body interaction. (Less)

New insights into the structure of exotic nuclei using the RISING active stopper

This conference paper outlines the operation and some of the preliminary physics results using the GSI RISING active stopper. Data are presented from an experiment using combined isomer and beta‐delayed gamma‐ray spectroscopy to study low‐lying spectral and decay properties of heavy‐neutron‐rich nuclei around A∼190 produced following the relativistic projectile fragmentation of 208Pb primary beam. The response of the RISING active stopper detector is demonstrated for both the implantation of heavy secondary fragments and in‐situ decay of beta‐particles. Beta‐delayed gamma‐ray spectroscopy following decays of the neutron‐rich nucleus 194Re is presented to demonstrate the experimental performance of the set‐up. The resulting information inferred from excited states in the W and Os daughter nuclei is compared with results from Skyrme Hartree‐Fock predictions of the evolution of nuclear shape.