Results of the IAEA personal dosimetric measurements programme in support of the international Chernobyl project

The film dosimeters produced by KODAK US Type 3 were distributed among residents of seven settlements of the three republics affected by the Chernobyl accident. Based on the testimony of 5641 dosimeters, it can be expected that 90% of the population received less than 1.2 mSv during 1990 - the year of measurement. Less than 2.5% should have received an annual dose of more than 6 mSv and only 11 people received irradiation at doses over 27 mSv. The data obtained on full-body counters for 9058 inhabitants show the range of average annual doses of internal exposure from 0.11 mSv to a maximum value of 0.99 mSv in a small settlement in Ukraine. The range reflects not only the variation in the values ​​of local contamination with cesium, but also the differences between settlements in the restrictions on the consumption of certain products. The results indicate that during the measurement program, internal exposure made a major contribution to individual doses. Although the relevant data are not presented in the work, but the results obtained are generally consistent with the results published by Soviet scientists. The purpose of the comparison of indicators for total body counters was to assess the overall quality of the measurements, primarily 134Cs and 137Cs, produced on devices in the areas affected by the Chernobyl accident. It should be remembered that the comparison was carried out 4 years after the accident. Therefore, the results do not necessarily reflect the quality of measurements made during the first months after the accident. The IAEA does not have specific criteria for evaluating the functioning of total body counters. However, the quality of the comparison results can be correlated with the requirements contained in the IAEA Safety Series No. 84, Basic Principles for Occupational Radiation Monitoring [6], paragraph 4.1.5., Which states that: In the case of routine individual monitoring of external radiation, the relative uncertainty from -50% to + 100% at a 95% confidence level is acceptable for annual dose equivalents in the region of one-fifth of the required limit. If, however, the values ​​are close to the annual limits, the relative uncertainties should not exceed -33% and + 50% at the 95% confidence level ..... Similar requirements should, in principle, also be applied in the case of routine individual monitoring for internal exposures, but in practice such small uncertainties as 50% are rarely possible. In 5 of the 36 measurements carried out at the institutes of the USSR (Table 8), the results were outside the range of ± 30% as compared with the reference values. One result was slightly more than 50% relative to the reference value. In the latter case, the measurement was made on an unshielded sample using a phantom twice the position of the Marinelli. Based on the distribution of the results of the comparison, it can be reasonably concluded that the institutions involved in the comparison are capable of measuring internal cesium with an accuracy that is acceptable and adequate for radiation protection purposes. It should also be noted that in 4 cases out of 5, when the results were outside the range of ± 30% of the reference value, measurements were made on phantoms representing children. Although the differences are not too large, they indicate the need for special attention to the calibration of meters intended for measuring children.