Neutron Activation of 74Ge and 76Ge

The upcoming GERDA and MAJORANA experiments will use germanium crystals, isotopically enriched in Ge-76 to search for the neutrinoless double beta decay (0 nu 2 beta). The very long half-life of 0 nu 2 beta (> 10(25) y for Ge-76) requires an extremely low background level. Neutrons induced by cosmic muons can be captured after thermalization by Ge-74 or Ge-76, followed by beta(-)-decay of Ge-75 and Ge-77 respectively. The prompt gamma-cascade after neutron capture and the beta-decay contribute to the total backround in these experiments. For a good estimation of the background the poorly known cross-sections for the Ge-74(n,gamma)Ge-75,Ge-75m reactions were measured using targets, isotopically depleted in Ge-76. Furthermore the prompt gamma-rays in Ge-77 were measured with isotopically enriched germanium targets. The results of the latter measurement were combined with the results of a dedicated coincidence measurement to reconstruct the prompt gamma-ray decay scheme.