Estimations of population doses and risk estimates from occupational exposures in Japan, 1978 Part 1. Determinations of organ or tissue doses and effective dose equivalents.

Abstract

The International Commission on Radiological Protection (ICRP) has proposed the concept of effective dose equivalent for the purpose of radiation protection programs in occupational exposures. Dose equivalent of radiation workers has been popularly evaluated from the readings of film badges worn mostly on the chest region of the workers. At the present time, the effective dose equivalents must be estimated from the film-badge readings. In order to simplify the determinations of the effective dose equivalents, ratios of organ or tissue doses to unit film-badge reading were calculated with the aid of the Snyder''s mathematical phantom constructed so as to simulate the Japanese body. The dose calculations were carried out on the organs or tissues related to stochastic effects of radiations. The energy and angular dependencies of organ or tissue doses were calculated using depth-dose curves experimentally determined with a phantom measurement. The effective dose equivalents were determined with the weighting factor recommended by the ICRP. The effective dose with respect to fatal malignant diseases was calculated using a modified weighting factor estimated from the excess mortalities of cancers caused by the atomic bomb radiations in Nagasaki. The effective dose is somewhat different from the effective dose equivalent and is used for the determination of malignancy significant dose which will be defined as one of the population doses in Part 2 of a series of paper. The organ or tissue doses were calculated for gamma-rays from 60Co and 137Cs sources and X-rays of 30, 80 and 140 keV. These doses are tabulated as a function of gamma and X-ray energies for various incident angles of radiations on workers. On the basis of these data, the effective dose equivalents and the effective doses were determined for the estimation of population doses in Part 2.