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HK: Hadronen und Kerne

HK 31: Nuclear Astrophysics II

HK 31.4: Gruppenbericht

Dienstag, 17. März 1998, 14:45–15:15, G

New Experiments on R-Process Nuclei in the ¹³²Sn₈₂ Region — •K.-L. Kratz — Institut für Kernchemie, Universität Mainz, Germany

The structure and decay of very neutron-rich isotopes in the vicinity of the far-unstable doubly magic nucleus ¹³²Sn play a crucial role in the description of the solar-system r-abundance peak at A≃130. In this context, experimental investigations of the classical N=82 ”waiting-point” isotopes are of particular interest. However, such studies were severely complicated in the past by (i) very low production yields and (ii) chemically non-selective plasma ionization modes at conventional isotope separators. Therefore, in recent years element-selective laser ion-source systems based on resonance ionization of atoms in a hot cavity have been developed – e.g. for ₄₇Ag, ₄₈Cd and ₅₀Sn – at the CERN-ISOLDE facility.
We will report here on our recent γ- and delayed-neutron spectroscopic studies of very neutron-rich Ag-isotopes.
Excited structures beyond the first 2⁺ level have been studied in the even-even ^122−128Cd-daughters. Furthermore, the long searched-for r-process ”waiting-point” isotope ¹²⁹Ag₈₂ could be identified unambiguously via its β-delayed neutron-decay mode. This isotope has with N-Z=35 the largest neutron excess observed in a decay study. The half-life of its πg_9/2 ground-state decay was determined to 46₋₉⁺⁵ ms. Possible implications of the new nuclear-structure results south of ¹³²Sn on the A≃130 abundance region of the astrophysical r-process will be discussed.