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Last Updated: Thursday, 31 July, 2003, 10:37 GMT 11:37 UK
Radiation lessons of Hiroshima bomb
Hiroshima after the bomb
The US dropped an atomic bomb on Hiroshima on 6 August 1945
A study into the impact of the Hiroshima bomb has concluded that current safety limits on radiation exposure are correct.

It is almost 58 years to the day since two atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki.

The bombs claimed the lives of about 250,000 people. They also provided scientists with unique data on how radiation causes cancer.

In the years since World War II, this data has been used to set safety levels for exposure to radiation everywhere from hospitals to nuclear power plants.

Radiation exposure

Professor Tore Straume and colleagues at the University of Utah, US, carried out a study to see if the data and, by association, current safety limits are correct.

The last major study into the impact of the atom bomb on Hiroshima was carried out in 1986.

The risks are pretty much what we thought they were
Dr Mark Little,
Imperial College London
It estimated the amount of radiation people who were killed by the bomb and those who survived it were exposed to.

However, scientists involved in that project had acknowledged that their figures may be wrong.

This was because they were based on estimates of how much radiation was emitted by the bomb.

The scientists were unable to accurately test how many high-energy or fast neutrons were released by the device.

These neutrons or particles are believed to have been responsible for one in five cancers.

A new test has enabled Professor Straume's team to accurately test for these particles.

They analysed metal lightning rods and gutters from buildings taken from Hiroshima after the blast.

They tested for a nickel isotope produced when particles released from the bomb hit copper.

They found that levels of neutron exposure were in line with previous estimates.

This led them to conclude that there is no need to alter existing estimates of the health effects of fast neutrons.

Writing in the journal Nature, they said: "These findings provide, for the first time, clear measurement validation of the neutron doses to survivors in Hiroshima."

Dr Mark Little of Imperial College London, UK, said: "The risks are pretty much what we thought they were."

In pictures: Hiroshima remembers A-bomb
06 Aug 01  |  Asia-Pacific

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