Absolute Measurements of the Disintegration Rates of Americium-241 Sources by Using Semiconductor Detectors

Low geometry a counting and α-particle/γ-ray coincidence counting were made to determine the absolute disintegration rate of an 241 Am source. Alpha particles were counted by silicon junction detectors and γ-rays by an Nal(Tl) crystalphotomultiplier system. The half life of the 60 keV level of 237Np was measured to check the effect of the coincidence resolving time in the absolute measurement of the americium source by α-γ coincidence counting; the half life measured was 6.3 × 10-s sec. The mean value of the absolute disintegration rate of a typical 241Am source measured by coincidence counting was 1.696 ×104 dps and the 90% confidence interval for the mean value was [1.679 ×104dps, 1.713×104dps]. Accurate absolute measurements by low geometry a particle counting are very difficult especially for very small semiconductor detectors because of the difficulty of measuring the accurate geometries.