New stack monitor concept and its design

External exposure due to radioactive inert gases fmm a stack presents important problems to the enviromnent 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. For evaluating the external exposure from a gaseous mixture of Kr and Xe isotopes in the environment, the usual methods are not satisfactory and are even meaningless when the fractions of radionuclides in the mixture gas change according to the storage or hold-up time. A new concept of stack monitor to measure the Photon energy dissipating rate, the photon dissipating rate, and the average energy is discussed. It is shown that this method simplified the evaluating procedures and improves the accuracy of gamma -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 electmnic circuit for pulse height weighing. (auth)