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Bochum 1998 – scientific programme

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HK: Hadronen und Kerne

HK 31: Nuclear Astrophysics II

HK 31.6: Talk

Tuesday, March 17, 1998, 15:30–15:45, G

Depopulation of the Kπ= 9 isomer in 180Ta (?) — •M. Loewe1, J. de Boer1, M. Würkner1, P. von Neumann-Cosel2, A. Richter2, C. Schlegel2, F. Käppeler3, M. Schumann3, J. Srebrny4, J. Iwanicki5, and P.J. Napiorkowski51Sektion Physik, Ludwig-Maximilians-Universität München — 2Institut für Kernphysik, Technische Universität Darmstadt — 3Institut für Kernphysik, Forschungszentrum Karlsruhe — 4Nuclear Physics Division, Warsaw University — 5Heavy Ion Laboratory, Warsaw University

The extremly rare isotope 180Ta survives in nature in an excited-state isomer (Kπ=9, Ex=75.3keV, T1/2>1.2x1015y). The direct transition to the ground state (Kπ=1+, T1/2=8.15h) is highly K forbidden, but if the isomer is exposed to an intense photon bath under stellar s-process conditions it might be depopulated to the ground state through an intermediate state. Therefore yet unknown low-lying intermediate states connecting the isomer to the ground state would hinder a s-process production of 180Ta. In our activation experiments different heavy-ion beams were used to Coulomb excite 180Ta-nuclei, stopped in catcher foils. After irradiation Ge-detectors registered the ground state decay of 180Ta recoils in the catcher foils. The experiments indicate a possible depopulation of the isomer to the ground state via a Coulomb excited intermediate state around 1 MeV. The consequences of a Coulomb excitation induced depopulation of the isomer for its production under s-process burning conditions will be discussed. Supported by the Volkswagen foundation.

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