Radiation risks. Study casts doubt on Hiroshima data.

Abstract

More than 5 years ago, the experts who calculate radiation risks began to be troubled by a nagging and unwelcome discrepancy in the data from the atom bomb blast at Hiroshima. Their uneasiness has grown steadily worse, and it now appears to be threatening the credibility of the world's most important database in this field, the 40-year-old studies of bomb-induced cancer in Japan. A report published this month by Tore Straume, a biophysicist at the Lawrence Livermore National Laboratory, is bringing new attention to this issue and may goad the U.S. government to invest in research aimed at resolving the uncertainties. Straume has shown beyond any doubt, say his colleagues, that there is a discrepancy between the measured level of neutrons emitted by the bomb in Hiroshima on 6 August 1945 and the neutron level that weapons experts calculate should have been generated. Straume and his Japanese partners have collected samples of concrete from various points around the city and subjected them to a new analytical technique - accelerator mass spectrometry - which provides a count of chlorine-35 and chlorine-36 atoms present. The ratio yields a reliable index of the number of low-energy or 'thermal' neutrons on the scene inmore » 1945. Straume's chlorine data show that there were between two and 10 times more thermal neutrons in Hiroshima than bomb experts had calculated.« less