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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 K^π= 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. Napiorkowski⁵ — ¹Sektion 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 (K^π=9⁻, E_x=75.3keV, T_1/2>1.2x10¹⁵y). The direct transition to the ground state (K^π=1⁺, T_1/2=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.