Beta-counting sensitivities of silicon surface barrier detectors

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Abstract
A study was made of the B-counting properties of 2 detectors: a needle probe 3 mm in diameter and 2 cm long, and a disc-shaped wafer detector 3 cm in diameter and 5 mm thick. These were exposed to thick sources of 131I, 24Na, 32P, and 42K having approximately 4 [pi] geometry for the probe and 2 [pi] 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 32P is 0.9 counts/sec. for a solution of specific activity 10-9 Ci/ml at 37[degree]C, with a background count rate of 0.3 counts/sec.; this compares favorably with geiger counters and Li-drifted Si detectors of similar dimensions.