Synthesis of historical research current in environmental radioactivity

Our knowledge about the environmental radioactivity has gathered during the past century. The time course of the research on the environmental radioactivity would be divided into three periods. The first period is the dawn of radiochemistry starting with the discovery of radioactivity, the second period is the worldwide contamination by nuclear explosion tests in 1950s and early 1960s, and the last period is the contamination by nuclear accidents coupled with an increasing peaceful use of nuclear energy.

The discovery of radioactivity by Becquerel in 1896 was carried out by investigation of the possibility that the fluorescence of uranyl compounds. Marie Curie and Pierre Curie showed that all uranium and thorium compounds have radioactive nature independent of chemical composition and found that some of the minerals were much more strongly radioactive than pure uranium itself. This observation led to the discovery of the new elements polonium and radium in 1898. The extensive search of new elements in natural minerals, from the end of the former century to the beginning of this century, is the dawn of the environmental radioactivity. Many new stable and radioactive elements were discovered with great efforts; researchers isolated unknown substances from various kinds of environmental materials under poor experimental condition. M. and P. Curie treated a huge amount of rock and isolated polonium and radium by careful purification of pitchblende; it would be the initiation of radiochemical analysis. However, it had been believed that elements are unchangeable forever until E. Rutherford and F. Soddy concluded with careful consideration for the reported observations that radioactivity was due to changes within the atom themselves. They proposed an epoch-making idea that transformation of the atoms of the original elements to new elements. The investigations done in those days are closely related to the environmental radioactivity.

The first bomb was tested successfully in 1945 and was the signal of the following nuclear explosive races. Many nuclear explosion tests were carried out in 1950s and in the early 1960s, especially those done at open air released large amounts and various kinds of artificial radionuclides into the environment. The artificial radionuclides released into the environment, however, have brought us tremendous increase in understanding of environmental radioactivity. The environmental behavior of the man made radionuclides was extensively examined in the atmosphere, hydrosphere, and biosphere because these radionuclides were the environmental tracer introduced as worldwide scale. For example movement, mixing and diffusion process of water mass in the ocean were studied with helps of tritium, carbon-14 and other radionuclides. Biological accumulation through food webs was well understood by analysis of marine organisms at different levels in the food chain. Analysis of transuranium nuclides, such as plutonium, americium, neptunium, gave us an understanding of chemical, physical and biological behaviours of these nuclides in the environment which did not exist before 1945.

Nuclear accidents at nuclear facilities related to nuclear bomb production have taken place from the beginning of the development. However, most of the accidents were hidden for a long time as military secrets. The atomic weapons complex called “Mayak” at Chelyabinsk province ofRussia was closed to people until 1992 in which at least two very large nuclear accidents occurred in 1957 and 1967 which resulted in severe environmental contamination. We experienced large nuclear accidents related to peaceful use of nuclear energy: the Three Miles Island accident in 1979 and the Chernobyl accident in 1986. As an increasing demand of nuclear power generation, the potential for nuclear accidents at nuclear power stations as well as related facilities will be still high in the future. Such accident influences a lot of people because most of the nuclear power stations are constructed near populated areas. In the case ofChernobyl accident, people have been evacuated from the contaminated area to safety area. The contamination spreads out to the forested area; thus, behaviour of radionuclides in forest ecosystem is the major concern of researchers after the accident. The knowledge about the behaviour of radionuclides in the forest ecosystem has accumulated significantly for these ten years; however, it would takes time to understand the whole picture.

The research on environmental radioactivity has progressed in connection with nuclear explosion tests and nuclear accidents, those are undesirable events for the development of nuclear energy and this situation may still continue in near future as the JCO accident, recently occurred at Tokaimura, Japan.

(text above is extracted from Noriyuki Momoshima, 2000. Journal of Nuclear and Radiochemical Sciences, vol. 1(1), 43-45)