RADIATION DETECTOR

PROBLEM TO BE SOLVED : To solve the problem that radiation cannot be detected with a high degree of accuracy in the background where nitrogen isotopes unrelated to the fracture of fuel rods are contained in an exhaust gas though there is a means for detecting the fracture condition of the fuel rods by detecting the concentration of a radioactive rare gas in an exhaust gas extracted from a main steam pipe as a means for detecting the fracture of the fuel rods in a reactor. SOLUTION : A means for guiding the exhaust gas SG and liquefying and coagulating a radioactive rare gas 15 by cooling the gas SG with a cooler 9 is provided to measure the energy of gamma rays of the liquefied and coagulated radioactive rare gas 15 with a radiation detector 12. In this way, a simple installation makes it possible to obtain the radiation detector whose detection accuracy for the radioactive rare gas 15 is enhanced.