A CALORIMETRIC MEASUREMENT OF THE DISINTEGRATION RATE OF A P32 SOURCE

Abstract

The calorimetric method of measuring sources is of value when the average energy per disintegration is known, and may be used to check the accuracy of an "absolute" beta counting technique. This paper describes a differential calorimeter designed for this type of measurement, and an experimental determination of the disintegration rate of a P32 source. The calorimetric measurement gave a value of the disintegration rate with a probable error of 0.7% differing by 1.8% from the result obtained from an absolute count of the β-activity. The absolute count was accurate to ±2%. The calorimeter has a sensitivity limit of less than 10 μw., and makes use of thermistors to measure temperature changes of the order of 10−3 °C.