A new passive dosemeter for γ ray monitoring has been developed using an imaging plate (IP), combined with a unique annealing process. In the application of IPto dosemetry, fading causes serious problems. The fading is considered to be caused by the recombination of holes and electrons trapped shallowly in the F centers, which have several activation energies. Appropriate post-irradiation annealing procedures allow elimination of trapped charges with low activation energies, and quantitative estimation of the radiation dose is possible. With the optimum annealing condition experimentally established to minimize the effect of fading on dose estimation, it has become possible to evaluate a one-month dose directly with reasonable accuracy from the photo-stimulated luminescence (PSL) density of the annealed IP. With the described dosemeter, a one-month integral dose was measured in practice at several locations over the period of one year. The results were compared with those obtained using a commercially available optically stimulated luminescent dosemeter.
It has been confirmed that, in the measurement of radon-in-water using liquid scintillation counting, the direct method is preferred to the extraction method, since the former is simple technique. With a counting time of 60 minutes, the minimum detectable radon concentration by the extraction method and the direct method were found to be 0.03 Bq/kg and 1 Bq/kg, respectively. The minimum detectable radon concentration of 1 Bq/kg attained by the direct method is sufficient to check the radon concentration in drinking water below the Maximum Contaminant Level (11.1 Bq/L) proposed by the U. S. Environmental Protection Agency. The total net counting rates were estimated by the zero level extrapolating method. The optimized window values of the 3 efficiency tracing points were 50 keV - ∞, 75 keV - ∞ and 100 keV - ∞. The efficiency tracing method has been proved useful with LSCs that are currently available in Japan.
Measurements of radon in water have been conducted by many investigators so far. While liquid scintillation counting is widely used for radon-in-water measurements in Japan, there are other available devices such as IM-fontactoscopes and atmospheric radon monitors with bubbling kits. In the present study, an intercomparison exercise was conducted for four devices using water samples with two different radon concentrations. The devices used are : a liquid scintillation counter, an IM-fontactoscope, a pulse ionization chamber with a bubbling kit and a radon monitor (which employs a silicon semiconductor detector) with a bubbling kit. As a result, there was a good agreement among the measured values for other devices than the IM-fontactoscope (differences were within±3%), The atmospheric radon monitors (with bubbling kits) could be useful for field surveys of radon-in-water, considering their portability. On the other hand, the values measured with the IM-fontactoscope deviated from other measure-ment values (47% for sample A and 22% for sample B) . The deviation might be caused by a calibration method for the IM-fontactoscope. Since the IM-fontactoscopes are used at some institutes in Japan even nowadays, it is necessary to check values measured with them for determination of radon-in-water concentrations.