Can a Detector in Live-Time Mode Give a True Count Rate?

Abstract

Count rate in the live-time mode of a nuclear detection system should ideally be directly proportional to the disintegration rate of the sample assayed. We examine the linearity of the relationship by measuring the deadtimes using two different detection systems. For the sodium iodide (NaI) crystal detector system, iodine-125 (¹²⁵I) was used with the two-source method and the results were confirmed by the decaying-source method in which indium-113m (^113mIn) was employed. For the cadmium telluride (CdTe) semiconductor detector system, the decaying-source method and ^113mIn were used. In both systems, we found that nonlinearity at a high count rate could be significant.