It's been nearly 58 years since an atomic bomb was dropped on the Japanese city of Hiroshima near the end of World War II. Now, on the eve of the blast's anniversary, the uncertainty surrounding radiation levels inflicted on survivors may finally be settled. A report published today in the journal Nature confirms earlier radiation results, thereby increasing confidence in estimates of cancer risk that are based on the data.

Survivors of the Hiroshima bomb gave scientists a rare opportunity to study what effect extremely high doses of radiation can have on people. The information is used to set safe levels of exposure and calculate cancer risks for radiation in other areas, from medicinal X-rays to nuclear power plants. Consequently, if the radiation levels from the bombs were underestimated--as some reports in the mid-1980s had suggested they were--the effects would be far-reaching.

The atomic bomb released two types of radiation, easily-detectable gamma rays and fast neutrons, which are harder to measure. Tore Straume of the University of Utah and Livermore National Laboratory and his colleagues used a new technique to measure miniscule amounts of a nickel isotope known as ⁶³Ni (formed when fast neutrons strike copper) around Hiroshima. The researchers analyzed a variety of surfaces, including rain gutters and roofs, located up to 1, 500 meters away from the blast site. The results confirm the earlier findings and provide "for the first time, clear measurement validation of the neutron doses to survivors in Hiroshima," according to the report. In an accompanying commentary Mark P. Little of Imperial College concludes that "the collective data from the survivors of the atomic bomb are likely to remain a valuable predictor of the risks of ionizing radiation."

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