The depth dose distribution in culture medium irradiated with 40kV X rays was measured by Fricke dosimeter. The measurement was conducted in three steps, i. e.,1) The yields of Fe3+ ions in various thickness of Fricke solution irradiated with 40kV X rays were measured.2) The effective attenuation coefficient pF was estimated. The effective energy, the effective attenuation coefficient in water and the effective mass energy absorption coefficient in the solution and in water were interpolated from the data summarized by Johns et al. (water was considered to be equivalent to culture medium. )3) The yields of Fe3 + ions were converted to the absorbed energy with G value which was interpolated from the data in ICRU report 17. Then the expre s s i on of the depth dose distribution in water was deduced. The Fricke dosimetry suits for the experiments with the cultured cells because the measurements can be performed in the same condition as irradiation of the cells provided that the culture dish is used as an irradiation vessel. The depth dose distribution in water indicated that t h e absorbed dose decreases with the depth in water with the similar steepness to that simulated by Monte Carlo calculation.

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A Monte Carlo code simulating electron-photon showers was developed using the conventional technique which separates the electron slowing down into the continuous process and the discrete one. All the interactions in the discrete process, those are inelastic scattering, bremsstrahlung generation and positron annihilation in-flight, were taken into account. The table storage and lookup method was adopted for randomly sampling the discrete processes. The tables were pre-digested by compiling the numerical data obtained from the deterministic calculations. The outline of sampling scheme and the details of calculational procedure are described. Some examples of the data preparation for sampling the electron energy at which a reaction occurs and the energy of emitted particles are shown for water. The present procedure is simple and useful when the development of the Monte Carlo code of electron-photon transport is undertaken.

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The exp o s ure on the mass examination of chest photofluorography of pupils and teachers in Osaka City was surveyed. The mass examination of the chest has been carried out at the time of the entry into the primary school(6 years old) and the junior high school(12 years old) for pupils and annually for teachers in Osaka Ciry.
One primary school and one junior high school were picked up. The exposur e s of ten pupils and ten teachers sgthpled randomly in each school were measured with a thermoluminescence dosimeter. The average exposure at the back skin was 70.6±30.7 mR for the 6 years old pupils,85.6±21.0 mR for 12 years old pupils and 131.5±43.7 mR for the teachers.
The International Commission on Radiation Protection (ICRP) has assigned a limit that the dose equivalent in the chest X-ray mass examination is preferable less than 1 mGy. However, this survey shows that the aim of the ICRP is not satisfied even in pupils of 6 years old. To reduce the population dose, it is necessary to reconsider how to carry out X-ray mass examinations which have been used.

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