ABSOLUTE MEASUREMENT OF DISINTEGRATION RATE OF RADIOISOTOPE SOURCES BY X-GAMMA RAY COINCIDENCE COUNTING METHOD

摘要

The absolute disintegration rate of sources of radioisotopes that decay by electron capture is determined by the X-gamma ray coincidence counting method. The counting system consists of an X-ray and a gamma-ray detector, two single channel pulse height analyzers, a fast-slow coincidence circuit and three scalers. The detectors are of scintillation type with a Nal crystal;the crystal for the gamma-ray detector is 13/4"φ x 2" and that for the X-ray detector is 2 mm thick to minimize the background effect caused by energetic gamma-rays, this effect being measured by inserting a copper plate of 0. 5 mm thick as an X-ray filter between the detector and the source. An A-l type low noise preamplifier with a gain of 25 is used to amplify output signals from the X-ray detector.