LABORATORI NAZIONALI DI LEGNARO
Nowadays we are all witnesses of competition of facilities at different countries to study unknown regions of neutron rich nuclei. Much effort are devoted to understand the role of neutron excess and its influence on nuclei in vicinity of closed neutron shells and whose structure is not yet fully studied yet. One of the means to investigate a nuclear structure is in b-decay. Once a nucleus is proven to exist, its b-decay properties, such as T and P, which are relatively easy to measure, can provide the first hints on the nuclear structure. On the r-process site, half-life of the "waiting points"(nuclei on closed neutron shells) has significant effects on the r-process dynamics and the abundance distribution. The actual side and the astrophysical conditions under which the nuclear synthesis takes place are still not certainly known - since r-process nuclei are difficult to produce and to study experimentally, input parameters for r-process calculations are mostly derived from theoretical models. As it has been seen lately, most of the theories have failed to reproduce newly measured half-lives of nuclei near shell closures. Going steadily towards unexplored r-process nuclei in an experiment allows for these theories to be well adjusted. Since a neutron emission turns to be more and more considerable channel in b-decay of nuclei further away from stability, usage of proper neutron detector to study their properties becomes indispensable. To conduct the appropriate investigations, in the frame of collaboration with JINR, Dubna, we built a new detection system at recently inaugurated ALTO ISOL-facility. The heart of our setup, designed and constructed recently at IPN Orsay, was the He 4p high efficiency neutron detector TETRA working in conjunction in a specially designed 4pb and a standard HPGe detectors. The development, realization and commissioning of the setup was one of the primary objective of my thesis. At the new setup installed, in the region of N = 50, we rigorously investigated b- and b-n decay of 80,82,83,84Ga, obtained with the laser ionization source, to measure T1/2, Pn , absolute branching ratios and to examine carefully its structure due to g–b–n coincidence spectra. In the vicinity of N = 82 we systematically measured half lifes of 123,124,125Ag, In, produced at ALTO with a hot plasma ion source, by neutron activity curves. Finally, for the first time we observed b-delayed neutron emission from 126Cd and proposed its Pn. Thus, we proved the ability of our detection system for both – T1/2, Pn, measurements; and spectroscopic studies. We discuss the structure of nuclei and compare our results obtained with existing systematics and predictions of theoretical approaches.

DATA: 06-12-2013