The UNSCEAR published recently its 1972 report. It reviews the levels of radiation received from all sources to which man is exposed. Despite the widening use of radiation-producing devices, the widespread radioactive contamination from nuclear weapons tests and the increasing applications of nuclear energy and radioisotopes, natual sources are the main contributors to the radiation exposure of most of the human population and are likely to remain so in the foreseeable future. With current technology and operational practice, if the nuclear power production were to stabilize at the estimated level reached by the year 2000, annual global radiation doses from the power production cycle might be as high as approximately 0.2% of those received annually from natural sources.
The paper describes some results on the simulated experiment by using an activable tracer to evaluate the protective effect of a fume hood and a glove box where highly hazardous materials should be handled. It is shown that the amount of aerosol to be inhaled by a worker during a standard operation time (10min) will be in the order of 10-5 of the amount handled in case of aerosol generation and 10-9 for usual chemical procedure. This suggests, that for an example, the amount of plutonium to be handled in the hood should be limited below 10μCi for usual procedure, in order to maintain one twentieth of the MPC level in the working area. Several types of simulated accidents during aerosol generation were tested using a glove box with leak rate of 0.1 volume percent per 2 hours. Any measurable air contamination was not observed near the working area, except for a few types of accident such as a cut finger and a pin hole of the glove.
The contents of 131I in the thyroid of radioisotope workers were measured with a large NaI (T1) detector. For this purpose, a practical and convenient method was developed to estimate the fraction of 131I in the thyroid of that in the total body, f2, as well as the contents of 131I in the thyroid. The observed value of 131I content in the thyroid varied to some extent with the difference of the relative position between the thyroid and the detector. Three per cent of the coefficient of variation. was observed at actual measurements for human subjects. The values of f2 for 63 people who inhaled 131I were determined. They fit a log-normal distribution on ranging widely from 0.17 to 0.68. The geometrical mean was calculated as 0.28. In addition, the change with time of the 131I contents in the thyroid was followed for 11 cases to determine the effective half-lives. These values ranged from 4.9 to 7.6 days and the mean value with the standard deviation was 6.6±0.7 days. This mean value is a little less than the value for the standard man (7.6 days) given by the ICRP.