Thermoluminescent dating and its application to gamma ray dosimetry

The author joined the research group at Kyoto University and tried to apply the method to the dosimetry of gamma rays from the atomic bomb. The original procedure of Kennedy was to use the powdered earthenware directly for the measurement, and we applied this method for gamma ray estimates. It was noticed that spurious thermoluminescence appeared due to the presence of a variety of minerals, and the accuracy of the measurement was improved by collecting quartz particles only from the powdered material for the dosimetry of the absorbed dose. This new technique was extensively used for the revised gamma ray dosimetry of roof tiles in Hiroshima and Nagasaki, and was further modified by Dr. Fleming at Oxford University and others. More precise quartz inclusion techniques (1970) and pre-dose dating (1973) have since been developed. Age of earthenware is estimated by dividing the measured accumulated absorbed dose by the annual dose. For dosimetry of absorbed gamma ray dose from the A-bombs, three glow curve peaks (1100C, near 2000C and 3250C) were used. The pre-dose method was used for the 1100C peak and the quartz inclusion technique was applied for the 2000C and 3250C peaks. Calculations should be corrected for the fading effect based on the 2000C peak. There are two ways for making the annual dose estimate (1) by measuring the concentration of U, Th, and K and indirectly calculating the dose, and (2) by directly measuring the dose using a TL dosimeter (calcium sulfate). We have used CaSO4: Tm developed by Matsushita Electric Research Institute. For the present reevaluation of the dose in Hiroshima, gamma ray dose in the area of 1000 m or more from the hypocenter should be measured. For accurate estimates the natural background must be measured precisely, and the annual dose measured by the method mentioned above. (author)