Abstract
By using Pb shield of 10cm thick, new methods were developed to estimate each components of environmental radiation doses measured with CaSO4: Tm thermoluminescence dosemeter (TLD-UD 200S). These methods aimed at estimating the air absorbed dose increment due to radioactive materials in the atmosphere or downward radiations released from nuclear facilities. As a preliminary step for the application to detect small dose increments, TLDs preirradiated by 2.2, 3.6 and 7.2μGy with a 60Co source were placed at a location of which background level was 55.5nGyh-1. Performance of the TLD system seems to be satisfactory for the practical use since discrepancy between estimated and given doses was less than 30% for a given dose increment of 7.2μGy. The responses of the TLDs to cosmic and natural gamma radiations were also investigated with various dosimetric methods. It was found that the responses of the TLDs to natural gamma radiations are in agreement with those inferred from other methods, but their responses to cosmic radiation were definitely lower.
