Far from stability: Investigations in mass A ~ 90 nuclei.

摘要

Modern gamma-ray spectroscopic techniques were used to study the neutron-deficient nuclei 92Pd, 92Rh, and 94Pd. Excited states in these nuclei were populated in the fusion-evaporation reaction using a 240-MeV 58Ni beam on a 40Ca target. Several detector arrays were employed at Argonne National Laboratory: the Gammasphere, the Microball charged-particle array, the Neutron Shell, and the Fragment Mass Analyzer.;Excited states in 92Pd were previously unknown. The current work reports identification of several transitions tentatively assigned to this nucleus. This nucleus is expected to exhibit experimental evidence of condensate-type neutron-proton pairing. This mode of pairing has not been definitively observed in this mass region. Comparison of experimentally observed energies of the newly identified states in 92Pd with shell-model calculations indicates a possible observation of a signature of np pairing.;Information about excited states and angular distributions of transitions from the nuclei 92Rh and 94Pd was utilized to evaluate the probability of an exotic decay mode of a long-lived state of 94Ag (not directly observed here). New transitions in both 92Rh and 94Pd were identified. An improved technique for angular distribution measurements was used to determine the multipolarities of gamma-rays and thus deduce the spins of the observed nuclear states. Such measurements were previously unavailable in any 92Rh states, nor in high-spin states in 94Pd. Information obtained from this study indicates that the exotic two-proton decay mode allegedly observed in 94mAg is highly unlikely to have the reported characteristics.