Laboratory for Radioecology, Nakaminato

Division of Radioecology

Scientific information on the transfer of radionuclides in the terrestrial environment to man is essential in the assessment of the radiation dose due to radioactive fallout and it is also one of the key factors in understanding the possible impacts resulting from potential or actual release of radionuclides from nuclear facilities.

The division is investigating radioecological studies of mathematical model on the transport of radionuclides from the terrestrial environment to the human body. Sampling methods and radiochemical techniques for the low level radiochemical techniques for the low level radioactivity survey are being developed.

Behavior of Radionuclides in Soil and Fresh-Water

The behavior of radionuclides in soil and fresh-water systems has been studied for elucidating their fate in the terrestrial environment. At present, special attention is being directed to agricultural plants. The research activities thus include investigations on the mobility of long-lived radionuclides in soil, which is influenced by such characteristics of soil as distribution coefficient (Kd) and cation exchange capacity (CEC), and by the chemical properties of radionuclides. In this context, measurement procedures have been developed for determining low-level beta emitters in environmental samples.

Cycling of Radioactive and Stable Elements in the Terrestrial Environment

The deposition of gaseous iodine onto agricultural products has been studies using an exposure chamber. Determination of iodine-129 and iodine-127 (stable iodine) in the air, soil, water and vegetation is carried out in order to investigate the migration of those nuclides in the terrestrial environment. Several trace elements (e.g. U, Th, Sr, REE) have also been analyzed in various environmental materials by ICP-MS and by NAA. Transfer of radioactive and stable nuclides from soil to agricultural products is studied in relation to various environmental and plant-physiological conditions.

Estimation of Oral Intake of Radioactive and Stable Nuclides

In order to assess internal radiation dose due to the environmental release of radionuclides from nuclear facilities, it is necessary to know the quantity of radionuclides ingested by inhabitants. A survey on food consumption has been carried out in Ibaraki Prefecture. Through the survey, critical group, critical nuclides and critical marine food have been selected in relation to the coastal release of low level liquid waste from a nuclear fuel reprocessing plant. The contents of radioactive and stable elements in food before and after cooking are under investigation. Removal radionuclides from drinking water, milk etc. is also studied.

[lodine exposure chamber] lodine exposure chamber: Transfer of gaseous radiodine to plant (deposition velosity) is investigated using this chamber under various environmental conditions.

Internal Dose Assessment due to Radionuclides in the Environment

Radioactivity in the human body, especially in bone, is determined to estimate equivalent and effective doses due to radionuclides released in the environment, such as radiostrontium and radioiodine, and naturally occurring radionuclides.

Transfer of Alpha-emitting Radionuclides in the environment to the Human Body

For the more toxic actinides and other alpha particle-emitting nuclides, daily intake, uptake and distribution in man is being studied. This is to obtain essential parameters for the prediction models for the body content of these nuclides through the ingestion and inhalation path way for the purpose of assessment of doses for the public.

Reference Japanese Man Studies

To establish mathematical models and database of the Japanese for use in dosimetry for radiation protection, daily intake and distribution in the body of various elements as well as masses and dimensions of organs and tissues, etc. are being studied in relation to the ICRP Reference Man. Analytical techniques are being developed and applied to further the aims of this research.

[Weight Ratio] Average weight of organs or tissues and the total body of the normal Japanese male (20 - 50 yr), and elative ratio to that of the Caucasian adult male (ICRP Publication 23).
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Major Publications

Nakajima, T.: Estimation of Absorbed Dose to Evacuees at Pripyat-City using ESR Measurements of Sugar and Exposure Rate Calculations. Appl. Radiat. lsot., 45, 113-120, 1994.
Uchida, S., Muramatsu, Y., Sumiya, M. and Ohmomo, Y. Biological Half-Life of Gaseous Elemental Iodine Deposited onto Rice Grains, Health Phys., 60, 675-679, 1991.
Yasuda, H. Use of Electrical Conductivity to Estimate Effects of Competing lons on Radionuclide Distribution Coefficients, Water Air Soil Pollut., 74, 1-7, 1994.
Tagami, K. and Uchida, S. Separation Procedure for the Determination of Technetium-99 in Soil by ICP-MS, Radiochim. Acta, 63, b 69-72, 1993.
Muramatsu, Y., Uchida, S., and Ohmomo, Y. Root-Uptake of Radioiodine by Rice Plants. J. Radiation Research, 34, 214-220, 1993.
Yanagisawa, K. and Muramatsu, Y. Transfer Factor of Technetium from Soil to Vegetables. Radiochimica Acta, 63, 83-86, 1933.
Yoshida, S., Muramatsu, Y. and Ogawa, M. Radiocesium Concentrations in Mushrooms Collected in Japan. J. Environmental Radioactivity, 22, 141-154, 1994.
Kawamura, H., Yamamoto, M., Igarashi Y., Shiraishi, K. and Ueno, K. Naturally Occurring 226Ra concentrations in Bone at Various Ages and ŚÁ Deses in Adults. Health Phys., 61, 615-622, 1991.
Shiraishi, K., Igarashi, Y., Takaku, Y., Masuda, K., Yoshimizu, K., Hongo, S., and Yamaguchi, H. Daily Intakes of 232Th and 238U in Japanese Males. Health Phys., 63, 187-191, 1992.
Shiraishi, K., Yoshimizu, k., Tanaka, G., and Kawamura, H. Daily Intake of 11 Elements in Relation to Reference Japanese Man. Health Phys., 57, 551-557, 1989.

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Laboratory for Radioecology, Nakaminato