The physicochemical form of uranium ( super(238)U) in the sediment of brackish Lake Obuchi was investigated using the standard procedures of sequential extraction. Approximately 60% to 70% of ...super(238)U was composed of the form bound to carbonates and iron (Fe)-manganese (Mn) oxides in silty sediments, whereas more than 50% of super(238)U existed in the minerals of sandy sediments. The proportions of super(238)U bound to carbonates in the sediments of brackish Lake Obuchi were larger than those in fresh-water lake sediments. Most of the uranium in the brackish lake sediment was considered to be mainly influenced by UO sub(2)(CO sub(3)) sub(3) super(4-) in seawater, judging from the fact that the super(234)U/ super(238)U activity ratios (1.13 to 1.16) of silty sediments were very close to that of seawater (1.14). The high correlation found between the super(238)U concentration in the sediment and the amount of organic matter demonstrated that organic matter acts as a scavenger for super(238)U accumulation on the lake bottom.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Japan's first commercial nuclear fuel cycling facilities, including a spent nuclear fuel reprocessing plant, are now under construction in Rokkasho, Aomori Prefecture (prefecture--an area of ...administration similar to a county in the U.S.). The reprocessing plant is due to be completed by 2004. We surveyed indoor and outdoor environmental gamma-ray dose rates throughout Aomori Prefecture from 1992 to 1996 to get background data before operation of the plant. Glass dosimeters were used to measure cumulative gamma-ray dose rate. The outdoor gamma-ray dose rates were measured at 109 locations in the prefecture. The indoor gamma-ray dose rates were measured at 81 locations, which were generally in a dwelling near the location of an outdoor measurement. The contribution of radionuclides in the ground to the outdoor dose rate was estimated by using in-situ gamma-ray spectrometry with a germanium detector. The spectra were measured at 20 locations used for the glass dosimeter measurements. The outdoor gamma-ray dose rate was higher in the Tsugaru area (western part of the prefecture) than in the Nanbu area (eastern part). Means of the dose rate were 28, 31, and 25 nGy h(-1) for the whole prefecture and Tsugaru and Nanbu areas, respectively. The dose rates in winter were lower than those in the other seasons due to the shielding effect of snow on the ground. Mean contributions of uranium series, thorium series and 40K to the dose rates were 7.7, 8.2, and 9.3 nGy h(-1), respectively. The indoor dose rate was generally higher than the outdoor one, and the mean ratio of indoor to outdoor dose rates was 1.42. Means of indoor gamma-ray dose rate were 41, 37, and 43 nGy h(-1) for the whole prefecture and Tsugaru and Nanbu areas, respectively. The average effective dose rate to people in the prefecture was estimated to be 0.24 mSv y(-1).
Temperature dependency of radiophotoluminescence glass dosimeter sensitivity was examined by irradiation of the dosimeter elements in an artificial climate experiment chamber. Two laboratories (A and ...B) independently measured the radiation dose of the elements irradiated simultaneously. The dosimeter elements were irradiated by y-rays from a combined source of
137
Cs (3.3 MBq) and
60
Co (1.9 MBq) at four different temperature levels; -10°C, 0°C, 20°C and 30°C. Statistically significant decrease of the sensitivity at low temperature was observed by both laboratories, however, declining rates of the sensitivity with temperature were different for each. Average decrease rates were 0.047±0.025% deg"
1
and 0.091±0.033% deg"
1
for laboratories A and B, respectively. The maximum declining rate of 0.052% deg"
1
and 0.17% deg"
1
were observed by A and B, respectively. The reason for this discrepancy between the two laboratories was unknown, and further study is required to elucidate this problem.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
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