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  • Author or Editor: Y. Takizawa x
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Abstract  

The direct transfer of organically-bound3H (OBT) of diet to that in the human body is reasonable, since the human body needs essential amino acids and fatty acids. Metabolic models of3H which were recently developed for the human body took this direct incorporation into account. Data for fallout3H in diet and human tissues were used to validate model parameters, although such data are relatively scarce. However, a simple equilibrium between dietary3H and human body3H was assumed for such validations. The simple equilibrium assumption means completely neglecting past3H concentration in the human body. When the model consists of compartments which have long mean residence times, estimated3H concentrations in the human body from the simple equilibrium assumption can differ significantly from results of adequate calculation considering contribution of past human3H concentrations. The examples of such calculations are described in this paper. Results of the calculations show that suitable environmental3H transfer models are necessary to use fallout3H data for the validation of3H metabolism models.

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Abstract  

Tritium (3H) concentrations in diet samples from Akita City, northern Japan, and in human tissue samples from the general population of Akita Prefecture were analyzed to study fallout3H transfer.3H concentrations in human soft-tissue samples have been previously found to be similar to those in diet samples. In this study, higher organically-bound3H (OBT) concentrations were found in human costal cartilage and sternum samples than in the soft-tissues. Mean residence times of OBT in the cartilage and sternum were estimated to be 57 years and <6 years, respectively, with a single compartment model which took into account compartment growth.

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Abstract  

Inhalation of tobacco smoke is ranked second to food as a source of210Pb and210Po exposure to man. Assay of210Pb and210Po in commercially available tobacco collected from many countries have been carried out to assess the potential risk from210Po present in tobacco.The range of210Po contained in the tobacco grands varied from 10.08 to 15.0 mBq/tob or 13.0 to 20.1 mBq/g and the mean was 11.6 mBq/tob or 15.4 mBq/g. During the International Standard Smoking process about 50% of210Po present in tobaccos was transferred into the smoke and the other 50% remained in the ash and butt. About 10% of the total210Po of tobacco was inhaled by smoke through mainstream smoke. One pack-a-day smoker inhaled 24 mBq of210Po per day through smoking and the annual inhalation was 8.8 Bq. The risk of mortality from lung cancer caused by210Po in tobaccos was 18 per million persons for the above model.

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Abstract  

In order to better understand nuclear energy, the radiation counter for public acceptance (PA) activities are now widely used. The radiation counter which detects -rays and -rays, respectively, has been developed and supplied commercially, but there is no counter for PA use which detects -rays. Plutonium has been becoming the center of public interest in regard to transportation by the shipAkatsuki-maru, Rokkasho Reprocessing Plant, and the prototype FBR (fast breeder reactor) Monju. People in general are very concerned about plutonium, which emits -rays, because of its toxicity and possible use in nuclear weapons. In this connection, we have decided to develop a portable -particle counter for PA activities which detects -rays easily. We use Si surface barrier type semiconductor as a detector, and the total system is compact, light in weight, easy to handle, and inexpensive. Four kinds of samples are prepared; soil gathered from a hot spring field, sinter (siliceous material deposited by springs), uranium ore, and monazite. People in general can easily understand the nature of -rays which exits around us.

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Abstract  

The paper describes the recent plutonium measurements on tissues taken at human autopsy on foodstuffs collected in northern Japan. Estimates of plutonium concentrations are made using the ICRP 30 metabolic model and is compared with the results of our measurements.

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Abstract  

High specific activity ratios of tissue-bound3H to free water3H were reported for foods in Europe und USA during 1970s and 1980s. To examine these high specific activity ratios, small number of some recent food samples imported from European countries were previously analyzed in our laboratory. The specific activity ratios obtained were around unity, and not so high as those reported by other investigators. To confirm our results, additional food samples were collected during 1988–90 and analyzed for3H. The specific activity ratios in the food samples were found to be around unity, and the previous results was confirmed.

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Abstract  

Americium and plutonium concentrations in food samples and human tissue samples were determined using alpha-ray spectrometry.Food samples, representative of the average dietar intake over a period of 30d in Japan, were pruchased in Akita during 1985 and 1986. The food was divided into six groups: cereals, vegetable, fruits/beans, seaweeds, fish/shellfish, and meats/eggs/milk. Most of the. total ingestion of both Pu and Am was contributed by seaseed and fish/shellfish. The concentration of Am in the other food groups was low.A compoarison of the measured241Am/239+240Pu ratio in human liver with the predicted value of the ICRP-30 or ICRP-48 model showed that the half-life of Am in the liver is approximately 2–10y. The human tissue samples were obtained from subjects who died in Akita and Niigata Prefectures in northern Japan during 1981–1984. The median concentration of241Am was 1.4 mBq/kg-wet in the stemum (n=11), 3.4 mBq/kg-wet in the liver (n=19), and 0.5 mBq/kg-wet in the lung (n=15). The ratio of241Am/239+240Pu was 0.34 in the sternum, 0.12 in the liver, and 0.14 in the lung.

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Abstract  

The Niigata Prefectural Govemment has been carrying out an environmental radiation monitoring around the Kashiwazaki Kariwa Nuclear Power Station. Most of the gamma-ray dose rate was dependent on the natural radiation from the ground. The investigations wanted to detemine the natural radiation level in the Kashiwazaki Kariwa area. Gamma-ray dose rates were measured with a scintillation detector. Additionally, the quantity of radionuclides and their contribution to the dose rate were obtained by an in situ measurement method.

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Abstract  

Natural and artificial radionuclide concentrations in sea sediments around Kashiwazaki-Kariwa nuclear power station have been investigated with respect to the particle size distributions and the ignition losses during assay. Plutonium concentrations around the south and north discharge area, ranged from 0.054 to 0.24 Bq·kg-1 (average 0.145) and 0.15 to 0.25 Bq·kg-1 (average 0.213), respectively. Plutonium concentrations were significantly related to erosion and accumulation processes of sediments in both south and north discharges. Additionally, the ratios of 239Pu to 240Pu were evaluated with ICP-MS to determine the origin of the Pu-isotopes. Uranium-238, 232Th and 40K were found in concentration range of 7.3–67, 12–100 and 260–560 Bq·kg-1 with mean concentrations of 20, 29 and 390 Bq·kg-1, respectively. It is assumed that the relatively high concentrations of the natural radionuclides such as U and Th are due to the presence of minerals (the south discharge regions). On the basis of these results, the origin of the Pu-isotopes was assumed to be derived from fallout of the past atmospheric nuclear tests.

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