The effect of x-ray summing in calibration of extended energy range GE detectors

Gamma spectrometric analyses of low-level samples are usually performed using close measuring geometry. In this measuring set-up the effect of the true coincidence summing (TCS) has to be taken into account. The detection of true coincidence sum pulse is possible when a nuclide emits two or more cascading photons within the resolving time of a spectrometer. The magnitude of summing depends strongly on the total and full energy peak efficiencies of the detector and on the decay scheme of the nuclide. In addition to summing of gamma rays, other radiation, especially X-rays, can be in true coincidence with the gamma rays. X-rays in cascade with gamma rays can originate from electron capture, positron decay, or internal conversion. The summing effects with most of the X-rays can be ignored for the p-type Ge detectors having thick dead layer. On the contrary, the detectors with a thin entrance window, e.g. n-type detectors and new extended range p-type detectors, can experience severe summing of X-rays and gamma rays. (au)