A-bomb radiation doses reassessed.

A-bomb radiation doses reassessed

A long-awaited reassessment of radiation dose measurements from the Hiroshima and Nagasaki atomic bombs is nearly complete, researchers report, and is likely to result in more stringent radiation protection standards. The new calculations are based on revised estimates of the yields of those bombs and make use of new computing techniques for measuring radiation exposures. Like previous reports (SN: 5/30/81, p.343), the latest findings are controversial.

Roger J.M. Fry of the Oak Ridge (Tenn.) National Laboratory and Warren K. Sinclair of the National Council on Radiation Protection and Measurements in Bethesda, Md., report that a new, computer-assisted dose measuring system adopted in 1986 has provided more detailed information about the World War II blasts. Fully revised risk estimates are not expected to be released until 1988. However, the scientists write in the Oct. 10 LANCET, it is probable that "future risk estimates for radiogenic cancer will be somewhat higher' than before.

Atomic-bomb survivors are the primary source of data on long-term radiation risks for humans. Those data are being reviewed by the Radiation Effects Research Foundation (RERF), an organization jointly administered by the Japanese Ministry of Health and the U.S.-based National Academy of Sciences. New findings by RERF will be taken into account by the International Commission for Radiological Protection, which sets worldwide radiation protection standards for patients, radiation workers and the general population.

RERF's latest revisions, according to Fry and Sinclair, include an increase of about 20 percent in the estimated total yield of the Hiroshima bomb. The potential for gamma radiation to penetrate into bone marrow and deep organs is also calculated to be higher than was previously assumed. Despite these two factors, each person probably received a lower radiation dose than was thought, according to the research. This conclusion was based primarily on the findings that ordinary house walls provide more protection than had been believed and the two bombs gave off only 10 percent as many neutrons as had been previously estimated. This appears to suggest that the increased frequency of cancer seen in A-bomb survivors was caused by smaller doses of radiation than was heretofore believed.

In its standard-setting deliberations, the International Commission will be faced not only with new data from the RERF but also with the vocal opinions of scientists who are publicly urging the commission to tighten its standards by as much as a factor of five. Toward that end, the commission was petitioned last month by 800 scientists--including two Nobel laureates and a participant in the Manhattan Project--to lower its dose limits for nuclear and other radiation workers from the current 50 millisieverts per year to 10 millisieverts per year.