Neutron Activation of ⁷⁴Ge and ⁷⁶Ge

G. Meierhofer^1a, L. Canella², P. Grabmayr¹, J. Jochum¹, J. Jolie³ and P. Kudejova⁴

¹ Kepler Center for Astro and Particle Physics, Eberhard Karls Universität Tübingen, D-72076 Tübingen, Germany
² Institut für Radiochemie, Technische Universität München, D-85748 Garching, Germany
³ Institut für Kernphysik, Universität zu Köln, D-50937 Cologne, Germany
⁴ Forschungs-Neutronenquelle Heinz Maier-Leibnitz FRM II, Technische Universität München D-85748 Garching, Germany

^a e-mail: meierhofer@pit.physik.uni-tuebingen.de

Abstract

The upcoming G_ERDA and M_AJORANA experiments will use germanium crystals, isotopically enriched in ⁷⁶Ge to search for the neutrinoless double beta decay (0ν2β). The very long half-life of 0ν2β (> 10²⁵ y for ⁷⁶Ge) requires an extremely low background level. Neutrons induced by cosmic muons can be captured after thermalization by ⁷⁴Ge or ⁷⁶Ge, followed by β⁻ -decay of ⁷⁵Ge and ⁷⁷Ge respectively. The prompt γ-cascade after neutron capture and the β-decay contribute to the total backround in these experiments. For a good estimation of the background the poorly known cross-sections for the ⁷⁴Ge(n,γ)^75,75mGe reactions were measured using targets, isotopically depleted in ⁷⁶Ge. Furthermore the prompt γ-rays in ⁷⁷Ge 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 γ-ray decay scheme.