Evaluation of Effective Dose for Exposures in The Environment.

It is often said that radiological protection is a practical science and I quite agree. There are many cases where decisions must be made even if the scientific knowledge is imperfect. In such cases, the decision should be made using the best scientific knowledge available at the time. Effective dose is a typical example of a useful concept for such decisions in radiological protection as a practical science. The biological effect of exposure to radiation below 100mSv is, as well known, not thoroughly elucidated; nevertheless, radiological protection needs to be implemented appropriately for the safe use of radiation which provides huge benefits to human lives via various applications such as nuclear energy and medical use. The concept of effective dose was invented more than 40 years ago by Professor Wolfgang Jacobi (Jacobi, 1975), and since its adoption by the International Commission on Radiological Protection (ICRP, 1991) has played an essential role in radiological protection as the basic protection quantity. I was lucky to get the chance to meet Professor Jacobi while attending his 60th birthday party which was held in 1988 at the Gesellschaft für Strahlenforschung (GSF) (now Helmholtz Zentrum München). At that time, Professor Jacobi was serving as the director of one of the research institutes of GSF. He was so kind to smile and talk to the stranger who joined the party by chance while studying at GSF for a single year. During the party, a scientific journal with articles dedicated to him and his work was presented to him as a gift. It was quite an inspiring moment, and I decided to continue working in the field of radiological protection. I remember, after returning to Japan, arguments with my colleagues on how effective dose is useful in radiological protection. I was in favour of using effective dose, but could not argue sufficiently about its merits at that time. The fact that effective dose has been used for more than 40 years has proved its usefulness. Dose coefficients for external exposures in the environment have been studied for a long time. The first comprehensive studies on this subject were those by Dillman (1974), and Poston and Snyder (1974). Since then, many researchers, myself included, have tackled this subject, mainly using computer simulations, and several articles have been published. Before effective dose was established, dose coefficients were calculated for the whole body and specific organs. After the invention of effective dose, dose coefficients were estimated mainly in terms of effective dose, and have been an essential input for dose evaluation in the environment.