Аннотация
The photo-induced depopulation of the quasistable isomer (t(1/2) greater
than or equal to1.2 x10(15) yr) in Ta-180 with angular momentum and
parity J(pi) = 9(-) at an excitation energy E-x = 75 keV was studied at
the new bremsstrahlung irradiation facility installed at the Stuttgart
4.3 MV DYNAMITRON accelerator in the energy range of bremsstrahlung end
point energies between E-0 = 0.8-3.1 MeV. The onset of the isomer
depopulation could be observed starting at an end point energy of E-0
approximate to1 MeV, i. e., at an intermediate state of Ta-180 at or
below that energy. Higher-lying intermediate states were found at 1.22,
1.43, 1.55, 1.85, 2.16, 2.40, 2.64, and 2.80 MeV. The extracted
integrated cross sections show a remarkably strong depopulation of the
Ta-180(m) isomer by photoexcitation. The results are compared with
previous experiments and recent quasiparticle-phonon model calculations.
Implications of the results for a possible nucleosynthesis of Ta-180 in
the s process and the neutrino process are discussed.
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