584. スタック・モニタの新しい考え方とその設計

抄録

External exposure due to radioactive inert gases from a stack presents important problems to the environment near nuclear power stations, and the monitoring of these gaseous effluents has been undertaken by measuring the gross radioactivities of gaseous effluents in Ci/sec, using a stack monitor. But, for evaluating the external exposure from a gaseous mixture of Kr and Xe isotopes in the environment, the usual methods are not satisfactory and even meaningless when the fractions of radionuclides in the mixture gas change according to the storage or hold-up time.
In this paper, for estimating theγ-exposure from the mixture gas, a new concept of stack monitor to measure the photon energy dissipating rate Σ(QEF), the photon dissipating rate Σ(QF)and the average energy E is discussed, and it is shown that this method simplifies the evaluating procedures and improves the accuracy of γ-exposure evaluation. Further, the design of a new stack monitor is presented, which consists of a NaI (Tl) scintillation head with a specially designed Pb shield cap and an electronic circuit for pulse height weighting.