Low-energy enhancement in the gamma-ray strength functions of Ge-73,Ge-74

The γ-ray strength functions and level densities of 73,74Ge have been extracted up to the neutron separation energy Sn from particle-γ coincidence data using the Oslo method. Moreover, the γ-ray strength function of 74Ge above Sn has been determined from photo-neutron measurements; hence these two experiments cover the range of Eγ ≈ 1-13 MeV for 74Ge. The obtained data show that both 73,74Ge display an increase in strength at low γ energies. The experimental γ-ray strength functions are compared with M1 strength functions deduced from average B(M1) values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in 73,74Ge are adopted in the calculations of the 72,73Ge(n,γ) cross sections, where there are no direct experimental data. Calculated reaction rates for more neutron-rich germanium isotopes are shown to be strongly dependent on the presence of the low-energy enhancement