Study on the found after for Cosmic ray monitoring at ground level in order to discriminater variable factors of environmental exposurc

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1. To evaluate cosmic ray flux with a 3"phiNai(Tl) detector, it is important to determine the pulse-height distribution below 3MeV. In the present study, cosmic ray fbx density was determined applying Nagaoka's experimental results. 2. Cosmic ray component were determined in the fall('92) and in winter('93). The ratios phiu/phie were 2.5 in the fall and 3.00 in winter. Cosmic ray exposures were, however, almost unchanged. 3. To elucidate the long term variation and the short term variation of cosmic ray flux density the models were developed. Cosmic ray photon flux was varied with atmospheric pressure. 4. It was found that cosmic ray photons were distributed below 17MeV, and incident photon spectrum could be determined with the response matrix of a 3"phiNaI(Fe) detector. Now, we are developing the response matrix of the detector used. 5. It was also shown that cosmic ray exposure could be determined based on the counting rate above 3MeV with a 3"phi plastic scintillation counter. The stability of the discrimination level was essential to carry out a long term monitoring of cosmic ray exposure.