ホスウィッチ型検出器を用いた肺モニタの校正

概要

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This paper describes a calibration method of a pair of 12.5cm diameter phoswich detectors for the measurement of the amount of Pu in lungs. The phoswich detector consists of a thin crystal (3mm) of NaI (Tl) backed by a thick crystal (50mm) of CsI (Na). The calibration factor obtained from a phantom was corrected for Pu isotopic composition and the X-ray absorption in the soft tissue. The X/α ratios of several Pu samples having different isotopic compositions were calculated, in order to take into account the difference of the isotopic composition used in the phantom from that of an inhaled person. For sixty male subjects, the chest wall thicknesses were measured using ultrasonic device, and an emprical equation, which expresses the relationship between chest wall thickness and body parameters such as weight and height, was derived. The minimum detectable amount of typical reactor-grade Pu, which was obtained by the phoswich detector assembly, was 7nCi for an average subject.