The development of a direct-gamma ray monitoring system for nuclear plants

An environmental monitoring system using a source modulation technique was experimentally developed for the measurement of direct gamma rays emitted from nuclear plants. It has a rotary collimator with which the gamma component arriving at a detector is modulated as a sine-wave function of time. The intensity (dose rate) of direct gamma rays is determined from analyzing the cross correlation power spectrum density of the detector output. The sensitivity and angular resolution of the system were examined by using a /sup 137/Cs source. The background component was reduced to less than 4% in comparison with the usual collimator. Direct gammas of 0.3 mu R/h (0.79*10/sup -10/C/kg/h) could be detected with an excellent angular characteristic.<
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