Beta-counting sensitivities of silicon surface barrier detectors

Abstract

l study was made of the 8-counting properties of two detectors: a needle probe 3 mm diameter and 2 cm long, and a disc-shaped wafer detector 3 cm diameter and 5 mm thick. These were exposed to thick sources of 1311, *'Na, 32P, and 42K having approximately 47r geometry for the probe and ' x geometry for the wafer. The absorbed energy spectra are shown, together with the resulting integral count rate as a function of discriminator level, and the dependence of these quantities on the sensitive detector volume is considered. The maximum practical sensitivity of the probe detector to 3 2 P is 0.9 counts,'sec for a solution of specific activity IO-8 Ci m1 at 3iCc, with a background count rate of 0.3 counts/sec; this compares farourably with geiger counters and Li-drifted silicon detectors of similar dimensions.