| Research Abstract |
Underground disposals of nuclear waste are considered to be indispensable for long-term isolation from the biosphere. The glass waste form will contain the highly radioactive isotopes extracted from spent nuclear fuel. Increasing crystallinity and alteration (metamictization) of waste glass by the effect of alpha-radiolysis and the associated release/retention of radionuclides are problem. Natural analogue is available to estimate the long-term behavior of the radionuclides. The objective is to establish the method of autoradiography of imaging plate (IP) system (R-AXIS-DS III) of block samples and the application of IP to natural analogues. The latently-stored radiation image is read out by measuring the intensity of the fluorescence with laser beam and IP has a sensitivity of about 100 times greater than that of conventional X-ray films.
We have described some characteristics of the IP for a two-dimensional position detector for radiations in uraninite, allanites, various minerals in
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JG-1a rock samples. The INAA determination of U and Th and emission spectral analysis of K in these samples are done. A spatial resolution is about 100 mum x 100 mum (i, e., a pixel). In the case of high-resolution IP (HR-III_N), the photostimulated light intensity per a pixel of 1% of K,1ppm of U and nuclides under U-series equilibrium, and 1ppm of Th and nuclides under Th-series equilibrium are approximately 1cph (count per hour), 0.1cph and 0.1cph, respectively. Shielding experiment of metal sheets indicates that the exposure of IP by K is due to the radiation of beta-ray but not the gamma-ray. We expected the distinction among the radionuciles using metal sheets for shielding, but it proved impossible. Screening of metal sheets sensitize the IP due to the bremsstrahlung of beta-ray from radionuclide in block samples, far from screening the low-energy gamma-ray. The fading of the latent image is significant and variable according to the circumstance. We are now doing the application of IP system to the Brazilian radioactive minerals. Less
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