STUDY OF NEUTRON AND MUON BACKGROUND IN LOW-LEVEL GERMANIUM GAMMA-RAYSPECTROMETRY

Cosmic ray induced neutrons and muons cause activation of nuclei. Usin g low-background detectors, constructed with strictly selected materia ls, and sufficient shielding from the surrounding environmental gamma- radiation, one can measure the activation products and deduce informat ion about the flux of neutrons and muons. The results of such a study can be used to improve the shielding for ultra-low counting spectromet ry systems. In this work two low-level HPGe detection systems have bee n used to study the thermal and fast neutron fluxes, as well as the mu on flux at three different experimental sites: on the surface, at a de pth of 15 m water equivalent (m w.e.) and at 500 m w.e. The study was based on measuring the activation of nuclei in the detector itself and in gold foils. The muons were identified due to their high energy dep osition in the detector crystal. Fast and thermal neutron fluxes have been measured since 1985 and estimates of the neutron and muon fluxes are given. The results are discussed and compared to the values obtain ed by the Kiel Neutron Monitor for the same time period.