APPLICATION OF AN IMAGING PLATE FOR EVALUATING THE UNCERTAINTY IN DIRECT ORGAN MEASUREMENTS DUE TO VARIATION IN DETECTOR LOCATION.

In direct organ measurements, there can be uncertainty to the quantified amount of activity due to variations in detector locations. Here, the authors demonstrate a new use of an imaging plate (IP) for evaluating this uncertainty. The method requires only that an array of regions of interest (ROIs) is set on a latent image obtained from the IP; each ROI conforms to an active area of the detector to be used. In this study, the proposed method was tested in an experiment using a realistic torso phantom containing an (241)Am liver source. The latent image of this source was obtained by irradiating the IP (20 × 40 cm(2)) from the anterior surface of the phantom. A comparison of responses between the IP and a high-purity germanium detector was made for 6 of the 144 circular ROIs arranged on the latent image, showing excellent correlation between the two sets of measures. The dispersion of the photostimulated luminescence values of the 144 ROIs was found to be 8.2% (1σ) and 1.09 as a log-normal scattering factor, which was expected to be the same as the uncertainty of concern in the present measurement with the HPGe detector.

Individual monitoring for internal contamination with plutonium compounds at JAEA-NCL.

This paper provides an outline of an individual monitoring programme for internal contamination with Pu compounds and some of the knowledge obtained from experience of inhalation incidents that occurred over the past few decades at the Japan Atomic Energy Agency, Nuclear Fuel Cycle Engineering Laboratories (JAEA-NCL). Most of the incidents resulted in minor exposure doses, being an average of 0.1 mSv at a mixed oxide plant and 1.5 mSv at a reprocessing plant. Only two incidents involving three workers resulted in exposure over the regulatory dose limits of that time. The maximum exposure dose, an effective dose equivalent of 90 mSv, was assessed for a worker involved in the incident that took place at the reprocessing plant in 1993. Only faecal measurements have been used in final dose assessments because alternative monitoring data have rarely been available. Further investigations on the physicochemical properties specific to Pu compounds in workplaces have therefore been needed to improve not only the accuracy of internal dose assessments but also the nasal swab method useful in deciding medical intervention.