New radiation study in Hiroshima lends support to current worker-safety radiation limits

Wednesday, July 30th 2003, 12:00 am

By: News On 6

58 years after Hiroshima was flattened by the first atomic bomb, scientists say radiation exposure standards used around the world do not require an overhaul.

After World War II, A-bomb data from Japan and survivors' medical histories were widely used to set individual radiation limits for gamma ray and neutron exposure to protects workers' health and predict radiation-induced cancers.

In 1987, some scientists questioned whether the standards were adequate, especially for neutrons. That's because detection methods used in 1945 were too crude to detect the radioactive products even a half-mile from the bomb's impact.

To settle the debate, researchers at the University of Utah isolated an isotope of the metal nickel _ produced when fast neutrons hit copper atoms. In Hiroshima, they measured trace amounts of the isotope in copper samples like lightning conductors, rain gutters, and roofs. The process took more than 10 years.

The amount of neutrons within a mile of ground zero made up only 1 percent to 2 percent of the total radiation dose suffered by blast survivors, the Utah team reports in Thursday's issue of the journal Nature. The new measurements are consistent with the limited measurements made in 1945.

``We can finally say that a large discrepancy in neutron dose to Hiroshima survivors does not exist,'' said lead researcher Tore Straume.

Scientists who reviewed the new data agreed.

``The collective data from the survivors of the atomic bomb are likely to remain a valuable predictor of the risks of ionizing radiation,'' Mark Little of Imperial College in London, wrote in a Nature commentary.

Some of the estimated 300,000 survivors suffer from an increase in leukemia and thyroid, colon and breast cancers, as well as heart-related diseases.

The United States dropped the first A-bomb on Hiroshima on Aug. 6, 1945, killing an estimated 140,000 people. A second A-bomb was dropped on Nagasaki with similar results.

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