Cosmic-ray induced background reduction by means of an anticoincidence shield

The cosmic-ray induced background of a spectrometer is reduced by means of an active veto shielding. Two such spectrometers have been developed: one equipped with a well type Ge detector and the other with a 50% relative efficiency coaxial Ge detector. In both cases, the active veto shielding consists of plastic scintillating plates and an anticoincidence electronic system. Although these devices have lower performances that those placed in an underground laboratory, their advantage is that they can be used in a normal laboratory environment. The background is reduced by 4 or 5 in the whole 30 keV to 2.7 MeV energy range and 5–10 in the energy range below 500 keV. Under these conditions, the count rates are smaller than 10−4 counts s−1 keV−1.