Variations of airborne radiation dose

The variation of spatial radiation follows four main patterns, considering the gamma ray component of environmental radiation : namely that due to rain fall as natural phenomenon, due to the weather of inversion layer, due to the fallout of the nuclear experiments in foreign countries, and due to the radioactive substances discharged from nuclear facilities. The requirements for the suitable system for the continuous measurement should be as follows : sensitivity for the measurement of the normal background of environmental radiation, short interval between time constant measurement, stability for long time, and easiness to arrange records, convertibility to dose or the information on environmental radiation, and small contribution of cosmic ray. Ionization chambers, NaI scintillation counters, and Ge (Li) semiconductor detectors are used. (Yamamoto, Y.)