This report describes a correction which is important in the determination of intensities of low energy gamma rays when a sodium iodide scintillation detector is used. The correction simplifies accurate intensity measurements by taking into account a major distortion of the scintillation spectrometer pulse height distribution.nIntensity measurements made with a scintillation spectrometer are complicated because a monoenergetic gamma ray produces a distribution of pulse heights. Different pulse heights result when different fractions of the gamma-ra) energy are expended in the crystal. The fractional energy expended depends on whether the gamma ray interacts by means of the photoelectric, the Compton, or the pair production process.nSince the probability of each of these interactions is a known function of energy, the intensity can measured either by determining the total number of interactions in the crystal (i.e., by recording pulses of all sizes), or by determining one portion of the pulse height distribution and interpreting it.
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