High-efficiency semiconductor gamma spectrometer with active shielding

A low-background semiconducting gamma spectrometer for measurement of fission product activities is described. A diffusion-drifted Ge(Li)-detector with a well of the 4.5 cm3 volume is used as an analyzing detector. An amplifying channel consists of a charge-sensitive field-effect transistor preamplifier and a spectro.metric linear amplifier. To reduce background loadings the detector is placed into a protection chamber of radiation pure iron with the 200 mm wall thickness. Besides utilization of passive shielding, active shielding is used on anticoincidences. An annular crystal NaI(Tl) is used as a protective scintillator. Optimum crystal dimensions are: the 210-220 mm height, 90 mm internal and 250-260 mm external diameters. The measurement results of activity of different samples carried out on the given low-background gamma-spectrometer are presented. The spectrometer permits to perform the spectrometric analysis of the samples of the up to 10-12 Ci/sample activity