Use of 137Cs standard source for the calibration of 125I monitors

In order to confirm the suitability of the K X-rays from 137Cs for calibration purposes, their pulse-height distributions were recorded under various conditions for a scintillation detector with a thin NaI(Tl) crystal and a low energy photon spectrometer comprising a high-purity Ge detector. In the use of these detectors, the pulse-height spectrum due to 32 keV K X-rays is significant even in the presence of a dominant background of 662 keV γ-rays, and the full energy peak is well separated from this background. It is shown that the background continuum can be corrected by the absorber technique. The reliability of the absolute intensity of K X-rays is discussed, and our experimental results are presented. As an example of the applications, we describe how 125I monitors were calibrated by the use of 137Cs standard source. (orig.)