Photoexcitation of 3.7 h 176Lum and its astrophysical consequences

Gamma-induced excitation of the 3.7 h half-life 176Lum was studied by high activity 60Co and 24Na γ-sources as well as bremsstrahlung from a 4 MeV electron linear accelerator. Photoactivation exchibited a steep rise in the energy region concerned, from 1.17 to 4 MeV. Observed abundance of the 3.6x1010y half-life 176Lu was proposed to be used for determining the age of the neutron capture s-process in stellar nucleosynthesis. However, the situation is complicated by the β-radioactivity of the isomer. Photoactivation may reduce drastically the half-life in stellar interior, so that it would reach the half-life of the isomer at 3.5x108 K temperature, guaranteeing thermal equlibrium between ground and isomeric states. This makes 176Lu unreliable as a cosmic chronometer. (author) 31 refs.; 3 figs.; 1 tab