Detection Limit and Precision in Photographic Dosimetry

概要

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The detection limit and the precision of dose estimation by photographic dosimetry were statistically analysed. The detection limit of Fuji Badge Film was found to be 9 mR for Ra γ-rays, and stack densitometry with three films improved the limit down to 5.6mR. It was found that the precision of dose estimation below 30mR was mainly dependent on the variances of the film background density. Latent image fading was found to cause no change in the standard deviation of the optical density. Accordingly, the effect of fading on the detection limit and the precision of dose estimation could be treated as if the sensitivity of the film had been reduced by a factor equal that of the fading. Discussion is presented on the relationship of the detection limit to the standard deviation of the background density and to the film sensitivity. The ratio of the background density standard deviation to the film sensitivity was found to be closely related with the detection limit of the film. The probability of detecting a positive dose beyond the variance of the background density was calculated for the case where the film was replaced every 3 months. Ten miliroentgen of γ-exposure can be detected in every film at a confidence level of 95%.
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