On the background counting rate in the alpha radiometers with AuSi surface-barrier detectors

The aim of the paper is to investigate the background counting rate in alpha-radiometers with AuSi surface-barrier detectors within the eneray interval of 3-10 MeV. It is shown that background pulses of nonradiation origin (supply-channel electromagnetic pickups and detector electric noises) as well as the effects of cosmic radiation on the alpha-radiometer background can be neglected. A series of measurements of backaround spectra after a preliminary hold-up of detectors during 8-20 days in vacuum and in tight vessels at an atmospheric pressure has been performed to estimate the contribution of emanation decay products to the α-radiation background counting rate. It has been found that the contribution of emanation decay products to the background counting rate accounts for 20-50% and depends proportionally on the area of the detector sensitive surface. For particular detectors the values of integral background counting rates vary, in the atmospheric air, between 0.2 and 0.32 h-1cm-2, while after hold-up in a tight vessel - between 0.09 and 0.16 h-1cm-2, no matter whether the measurements are taken in vacuum or at an atmospheric pressure. The analysis of obtained results has shown that the differential background counting rate of a semiconductor detector having a great sensitive surface (7x10cm2) and high energy resolutian (80-120 keV) constitutes less than 0.01 h-1cm-2. At such background values it is possible to identify and measure activities of the order of 10-14 -10-15 Ci in a sample