Calibration of a dual poswich detection system for measuring plutonium-239 and americium-241 in lungs

Conventional whole body monitors, although able to measure the characteristic 60 keV gamma radiation from 241Am are predominantly from X-rays of energy 14-20 keV. An accepted technique for the in-vivo measurement of 239Pu is being implemented at the Lucas Heights Research Laboratories (LHRL), based on counting the 239Pu X-rays with a pair of phoswich detectors placed over the subject's lungs. The attenuation of 239Pu X-rays escaping from the lungs depends strongly on the composition of the intervening tissue and thickness of the chest wall. Therefore, when a phantom is used to calibrate a detection system for in-vivo 239Pu monitoring, it must be constructed so that it accurately simulates body tissue at these X-ray energies. to satisfy this requirement at chest phantom was borrowed from the International Atomic Energy Agency (IAEA). The LHRL dual phoswich detection system and the calibration technique are described. Preliminary phantom calibration results obtained with both 239Pu and 241Am labelled lungs are discussed. Factors that affect the application of these calibration data to measurements on humans are also briefly discussed