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.
It is necessary to know the dose distribution in an irradiated body to evaluate patient doses during radiographic procedures. In this paper, we calculated dose distributions in an irradiated body on the conditions of actual radiographic exposures, by means of a Monte Carlo code with a human voxel phantom. The human voxel phantom, which was used in this calculation code, was constructed with voxels specified as each of soft tissue, lung, bone or air. The shape of this voxel phantom can be changed unrestrictedly by alteration of the voxel size and/or its material which is specified to each voxel. This calculation code, which gives a dose distribution data, is useful in medical exposure analysis, for example, variation of patient doses with exposure conditions or evaluation of organ doses. The dose distributions in a chest radiographic examination and a abdominal examination were calculated by this code. The isodose curves in these exposures were distorted in the lung area, and it was found that the lung having low density influenced the dose distribution from both primary and scattered photons.
From a practical angle of view to estimate the protection factors (PFs) provided by full-face masks, a number of protection factors were measured with a man-test apparatus just before the wearers started to do radiation work in radiation controlled area. PFs of the total number of 2, 279 cases were measured under five simulated working conditions. The measured PFs were widely distributed from 2.3 to 6, 700. About 95% of workers obtained PFs more than 50, and about 64% showed much higher PFs more than 1, 000 due to good fitting. In the case of some persons, the measured PFs irregularly varied and changed to a large degree. This method is a reliable technique that has been confirmed to protect unexpected internal exposure. From the results obtained, the method should be necessary to provide a better mask and higher PF for each worker.