NEUTRON-INDUCED ACTIVITY IN NATURAL AND ENRICHED GE-70 DETECTORS

The results of irradiations of isotopically enriched and natural Ge de tectors with a neutron beam are presented. The analysis of the gamma-r ay lines generated by decay of neutron induced unstable nuclei have pr ovided us with a direct measurement of relevant interaction cross sect ions. Within a factor of 2, measurements and predictions are in good a greement. These results have important implications for the instrument al background in astrophysical gamma-ray spectrometers using germanium detectors, We confirm the reduction of the beta-background component, which dominates the continuum background in the 0.1-1 MeV energy rang e, using Ge-70 enriched detectors. We clearly identify beta(+) decays inside the detector as a significant source of continuum background in the 1-4 MeV energy range, This component is about 2 times more intens e in Ge-70 enriched detectors than in natural ones. This is mainly due to the enhanced yield of Ge-69 and Ga-68 isotopes. The choice of eith er natural or Ge-70 enriched as optimum detector material depends on t he energies of astrophysical interest. Detectors made of enriched Ge-7 0 are more appropriate for studies at energies below 1 MeV. For higher energies natural germanium is slightly better. The possibility of rej ecting most of beta-background component by applying alternative analy sis techniques makes natural Ge an appropriate material for future gam ma-ray spectrometers.