Daily Mail (Reino Unido) online

Jawbone from Hiroshima victim reveals the terrifying radiation doses citizens were exposed to after the atomic bomb was dropped in 1945

Publicado em 30 abril 2018

Scientists have calculated how much radiation the people of Hiroshima may have been subjected to after the 1945 bombing, using tissue from one of the victims for the first time.

The study provides unsettling new insight on the effects of the nuclear fallout after the bomb was dropped; while thousands of people were killed in the initial blast, thousands more suffered at the hands of radiation sickness in the months to follow.

Using a technique designed for dating fossils and archaeological artifacts, researchers have analyzed a fragment of a jawbone from a Hiroshima victim, uncovering radiation levels nearly double the fatal dose.

The study relied on technique known as electron spin resonance spectroscopy to retrospectively measure the radiation doses Hiroshima victims were exposed to 73 years ago.

Up until now, the researchers say, samples of human tissue from the site have never been analyzed for this purpose.

The measurements showed a dose of roughly 9.46 grays (Gy) in the Hiroshima jawbone – a high dose, according to the team.

‘About half that dose, or 5 Gy, is fatal if the entire body is exposed to it,’ says Oswaldo Baffa, Full Professor at the University of São Paulo's Ribeirão Preto School of Philosophy, Science & Letters (FFCLRP-USP), who supervised the study.

The latest work builds upon research started in the 1980s under the leadership of physicist Sérgio Mascarenhas, Full Professor at the University of São Paulo (USP).

In the decade prior, Mascarenhas discovered that X-ray and gamma-ray irradiation induced a phenomenon known as paramegnetism in human bones – meaning they become weakly magnetic.

The process causes the sample to lose electrons, revealing how much radiation the material received.

After first using the technique to date archaeological remains, including skeletons of prehistoric animals and ancient utensils, Mascarenhas tested it on bone samples contained at Hiroshima University in attempt to measure the radiation.

The mushroom cloud over Hiroshima on August 6, 1945 is pictured

And, this experimentally proved that the method worked, the researcher says.

In the decades since, it has become far more precise thanks to recent advancements in technology, allowing researchers to differentiate between radiation from the attack and the background signal.

‘The background signal is a broad line that may be produced by various different things and lacks a specific signature,’ Baffa said.

‘The dosimetric signal is spectral. Each free radical resonates at a certain point on the spectrum when exposed to a magnetic field.’

The new study used tiny, millimeter-scale pieces of the same jawbone analyzed in the earlier work.

Researchers irradiated the samples again, calibrating for each of the different pieces, and measured how the signal rose.


The first atomic bomb was dropped on the Japanese city of Hiroshima on 6 August 1945 by an American B-29 bomber dubbed the Enola Gay.

The 9,000lb uranium-235 bomb exploded 1,900 feet (580 metres) above the ground, killing between 60,000 and 80,000 people instantly, some vanishing instantly from the heat of the vast explosion.

Others died as fire ripped through the city and some 135,000 people in total are thought to have perished from radiation sickness.

The blast flattened more than six square miles (10 square km) of the city, with fires burning for three days, leaving thousands of survivors burnt and homeless.

With major buildings like hospitals destroyed and more than 90 per cent of the city's doctors and nurses killed in the blast, there was little help available to the injured.

Ten years later, the longer-term effects of the bomb were being noticed, including a rise in leukaemia - a blood cancer not included in the study.

The cancer was said to disproportionately affect children, with cases appearing two years after the bomb and peaking four to six years later, The IBT reported.

The Radiation Effects Research Foundation estimates 46 per cent of leukaemia deaths at the bomb sites from 1950 to 2000 were due to radiation from the bombs, with 1,900 cancer deaths linked to the atomic bomb, in total.

According to the researchers, the measurements obtained in the study line up with estimates made previously using non-biological samples, including brick and roof tile fragments from the sites, and biological techniques based on survivors’ DNA.

The team is now working on a technique that’s even more reliable than the latest work, which they say is the most precise measurement yet.

‘There were serious doubts about the feasibility of using this methodology to determine the radiation dose deposited in these samples, because of the processes involved in the episode,’ said Angela Kinoshita, a professor at Universidade do Sagrado Coração in Bauru, São Paulo State who conducted the new research as a postdoctoral scholar.

‘The results confirm its feasibility and open up various possibilities for future research that may clarify details of the nuclear attack.’