Muon and neutron-induced background in gamma-ray spectrometry

A low-background γ-ray spectrometer for environmental surveillance, emergency response, and environmental health research has been constructed. It consists of a 132% efficient HPGe detector, graded lead shielding, and muon-rejection shielding, as well as external steel and building shielding. Detailed operation of the γ spectrometer and all of its components is described. Cosmic-ray muon and cosmic–neutron-induced background was accurately measured, and is discussed. We have achieved an overall background reduction by a factor of 9436 relative to the ambient level. Our integrated background rate in the γ energy range of 50–2700 keV was measured as 2.3 counts per min, corresponding to 15 counts ks−1 kg−1 Ge. Future directions in low-background γ spectroscopy at our facility are described.