In order to clarify the diminution characteristics of terrestrial gamma rays due to snow cover, a series of measurements of gamma ray dose rate and flux density was performed on a rice field with and without snow cover, in which the distribution of both the radiation field and the snow depth seemed to be uniform. The diminution factors for the dose rate and the flux density derived from the measurement and various corrections, such as for the contribution of cosmic ray, self-contamination of ⁴⁰K, and radon groups, showed a good agreement with those derived from Monte Carlo calculations. It was also shown that the melted snow water and the water content in the soil, in addition to the snow cover itself, can be significant factors affecting the diminution of terrestrial gamma rays, and that the accuracy of the evaluated contribution of radon and its daughters in air plays an important role for evaluation of the diminution factors.

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The distribution coefficient (K_d) of material between soil and soil solution is one of the most important factors in evaluating the transport of pollutant from soil to plant root. However, K_d value varies largely depending on the environmental conditions. Therefore, careful examination for conditions is necessary when reported K_d value is to be used for assessment of material transport in the ground.
In this study, effect of three environmental factors (temperature, soil-pH, and co-existing ions) on K_d of zinc was investigated by batch and column experiments. The results obtained are as follows:
1) Linear relationship was derived in the batch experiment between logarithm of K_d of zinc and that of cation equivalent in the equilibrium solution.
2) Effect of soil-pH on K_d of zinc became larger at lower ion concentration.
3) Effect of temperature on K_d of zinc was relatively small compared with the effect by the other two factors.
4) Physicochemically, equilibrium soil must be used for K_d determination by the column method. Ten pore volumes of influent solution were required to get the stationary ion composition in the column effluent.
5) K_d value determined by the column method was almost equal to that determined by the batch method.

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In radiobiological studies on inhaled plutonium in experimental animals, radioactivity initially deposited on alveolar region is required for calculating absorbed dose and therefore determining dose-response relationship. To reduce the error related to variation within the sample of animals we intend to use in vivo detection of plutonium by whole body counting procedures to determine the initial alveolar deposition in each animal. The periodical in vivo counting also permits us to obtain an accurate retention curve with a small number of animals. It is concluded that the in vivo detection developed in the present work provides a powerful means to determine the initial alveolar deposition of the plutonium-exposed rats.

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A computer code, FANTOME-90, was developed to calculate the equivalent doses in organs or tissues and the effective dose as well as the effective dose equivalent by the Monte Carlo method for external photon irradiation. The code treats a mathematical human phantom with movable arms and legs, which has been derived from the MIRD-5 phantom. The code enables to make the phantom take any posture by specifying the angles of each part of its arms and legs and wear individual monitors on its surface. The MORSE-CG code is incorporated in the FANTOME-90 code to calculate the photon transport from a source to the organs or tissues. The effective dose equivalent was calculated for this phantom in a standing posture and compared to that calculated for the MIRD-5 phantom. A good agreement obtained between them shows that the modification of the original MIRD-5 phantom gives no significant effect to the dose calculation. The values of effective dose calculated in different postures are given as an example.

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