Estimation of effective dose equivalent based on external photon energy spectra given by reactor operation

Effective dose equivalents in practical use were estimated in outdoor fields and in a reactor room of the Kyoto University Reactor on the basis of the energy distributions of the external photons. Gy to Sv (R to rem) conversion factors for respective organ or tissue of Japanese reference man were determined referring to the results by T. Maruyama et al., T.D. Jones et al., R. Kramer and G. Drexler in the energy region from 0 to 10 MeV. Differences between the anterior and the posterior exposures of workers were evaluated in the natural environment and in the controlled area of workplace using thermoluminescence dosimeter. The ratios of the effective dose equivalent to the exposure was almost constant in the various natural environmental conditions, with the exception of the sky shine gamma-ray field, while its ratio changed by almost 5 percents depending on the energy spectrum of the measuring point in the reactor room. It also became clear that the effective dose equivalent varied remarkably with the direction of incident photons on a human body when they were dominantly composed of the low energy photons below 0.4 MeV in the reactor room. (author)