RADIATION DETECTOR

PURPOSE:To hold the sensitivity of a radiation detector stable even when it is used under high-temperature conditions by using a mixed gas of gaseous He and gaseous Ar as ionizing gas, and setting the weight mixing ratio of the gaseous Ar to the whole mixed gas within a specific range. CONSTITUTION:An ionizing gas 6 is charged between a cathode electrode 1 and an anode electrode 2 which are applied with a DC voltage and radiant rays are detected with an ionizing current at the time of radiation incidence. Then the mixed gas of gaseous He and gaseous Ar is used as the ionizing gas 6 and the weight mixing rate of the gaseous Ar to the whole mixed gas is set to 0.01-0.1. The gaseous Ar is charged as the ionizing gas 6 together with the gaseous He from the beginning, so even if an impure gas is produced at a high temperature, a W value which is a parameter of ionization probability does not vary. Further, the mixing ratio of the gaseous Ar at the time of charging is set to 0.01-0.1 and then the W value is held nearly constant within this range.