History of Radiation Research in Japan-Environmental Studies-

Abstract

Radiation research in Japan started after atomic bomb attack to Hiroshima and Nagasaki in summer 1945 as far as environmental study is concerned.
The next important event was the radioactive contamination of tuna-fishing boat Fukuryumaru no.5 in March 1954. This was caused by fall out ofsubstantial amount of radioactive particles produced by a large scale hydrogen bomb explosion test carried out at Bikini atoll.
Radioactive contamination of fishing boat and tuna, and exposure of fishermen to radiation gave great fear to the public of Japan. In addition to marine contamination it was found that terrestrial environment including agricultural crops and others were also contaminated by radioactive fallout.
Therefore, research scientists of various universities and research institutes set up many investigation teams of different specialities such as agriculture, fisheries, meteorology, veterinary science and others.National Institute of Radiological Sciences was establishes in 1957 and Japan radiation Research Society started in 1958.
During these period, investigation on the distribution and concentration of various fission products(¹³¹I, ⁹⁰Sr,¹³⁷Cs etc.)and neutron-induced nuclides(⁶⁰Co,⁶⁵Zn,⁵⁴Mn etc.) in environment including food materials and humans.
By the information is obtained from these investigations, useful knowledge on nuclides transfer mechanisms (Sr-Ca discrimination, relation between fall out rate and accumulated deposit in plants, and chemical states of nuclides etc.) and transfer coefficients of radionuclide were given to our research fields. Transfer coefficient of radionuclides such as air to plant, soil to plant, water to aquatic organisms were utilized for estimation of future radionuclide concentration in ecosystems and radiation dose to man.As nuclear power production started in Japan, the environmental radiation safety became so important.
Informations obtained by the past radiological studies in the environment were very useful for this purpose.
Furthermore, pilot plant for reprocessing of spent nuclear fuel in Tokai needed the same kind of transfer coefficient of many different radionuclides. For that purpose, a great effort to get such informations was made by field studies, experimental studies considering different chemical states of nuclides and also stable nuclide concentration studies. Difference of radionuclide metabolism among different age groups in man and experimental animals was studied with emphasis on very young stage of man an animals.
Natural radiation studies were also carried out including terrestrial radiation, cosmic radiation and natural nuclides in food and radon with its progeny.