Gamma-ray strength functions in 74Ge

The germanium isotopic chain is of interest for a variety of applied nuclear science purposes due to its presence in high-resolution solid state and scintillation detectors and its use as a density-matching diagnostic constituent in plastic ignition capsules at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). In particular, it is essential for use in extracting the neutron capture cross section for astrophysically relevant neutron energies from germanium nuclei seeded into NIF capsules observed using the Gamma Reaction History (GRH) detector system. These Ge(n,γ) experiments will be used to establish the utility of NIF to perform neutron capture cross section measurements for the interpretation of s-process abundance data.
To study the γ-ray spectrum from excited states in germanium isotopes a combination of experiments using neutron capture and alternative reaction techniques is proposed in an international collaboration. These experiments will take place using thermal neutron capture at the Budapest neutron center, the STARS-LIBERACE (LBNL) and AFRODITE (Capetown) spectrometers for discrete spectroscopy measurements, the CACTUS array at the University of Oslo and the bremsstrahlung facility at ELBE of HZDR for statistical γ-ray measurements. The first part of this contribution presents photoabsorption cross sections determined from nuclear-resonance fluorescence (NRF) experiments performed at the bremsstrahlung facility γELBE. Strength functions deduced from the present NRF experiments are compared with the ones obtained from experiments using (3He,3He') reactions at the cyclotron of Oslo University.
The second part considers calculations of strength functions within the shell model that are analogous to the ones earlier discussed for Mo isotopes. The results of calculations of low-energy M1 strength for 74Ge are compared with experimental strength functions deduced from the (3He,3He') experiments. Predictions for the M1 strength in heavier Ge isotopes are shown.