Calibration of a very large ultra-low background well-type Ge detector for environmental sample measurements in an underground laboratory

A very large (903 cm3, 4.8 kg of Ge) ultra-low background well-type Ge detector has been installed in the Modane underground laboratory. This device is currently used in environmental studies, when only small samples are available and containing low levels of radioactivity. The main characteristics of the spectrometer will be presented. The calibration procedure—a mixture of experimentally measuring the photon attenuation of the sample matrix and Monte Carlo simulations using GEANT and the DECAY code—will be described.