Modifications to the inverse-square law of radiation detection for finite sized detectors

Abstract The inverse-square law model for detection of radiation from an isotropic source deviates significantly from measurements when the distance to the source is comparable to the size of the detector, and when the detector distance is not known accurately. An improved description requires a knowledge of the solid angle of the detector as viewed from the source, and the allowance for a distance measurement offset. Corrected detection rate vs distance models are presented for the cases of circular and rectangular detectors, when the source lies along the central axis of the detector. The models, including a distance offset, are in good agreement with the measured detection rates of a gamma radiation source using a CosmicWatch detector, in common use in educational settings.