Researchers Identify How Much Radiation Hiroshima Victims Were Exposed to

The scientists say their research is the first to use a human bone to precisely measure the radiation absorbed by an atomic bombing victim

Hiroshima the day after the nuclear bomb was dropped. Commons

On the morning of August 6, 1945, an American B-29 bomber dropped the first atomic bomb used in warfare on the city of Hiroshima, Japan. The nuclear bombardment decimated the city, killing between 90,000 and 166,000 people in a four-month period following the explosion.

Today, a rebuilt Hiroshima, home to a population of almost 1.2 million, renders the devastation inflicted on the city seven decades ago almost invisible.

But evidence of the atomic bomb lives on in the bones of victims of the blast. A recent study published in the journal PLOS ONE used the jawbone of one person who was less than a mile from the bomb’s hypocenter to reveal exactly how much radiation was absorbed by the city’s population.

As Laura Geggel reports for Live Science, the research team used a technique called Electron Spin Resonance spectroscopy to learn the jawbone contained 9.46 grays, or Gy (the unit to measure absorbed radiation), double the amount it would take to kill someone if their entire body is exposed.

The researchers say their work is the first to use human bones to precisely measure the radiation absorbed by atomic bombing victims. However, as the Washington Post's Kristine Phillips points out, in the late 1990s, a team of scientists from Japan were able to measure the radiation dose that nasopharyngeal cancer patients had absorbed from radiotherapy by studying their jawbones.

The new research is thanks to advances in technology. According to the study, in the 1970s, co-author Brazilian scientist Sérgio Mascarenhas discovered that X-Ray and gamma-ray radiation exposure caused human bones to become weakly magnetic. While his initial idea was to use his observation toward the archaeological dating of bones of prehistoric animals and humans in Brazil, he soon decided to test his methodology on nuclear bombing victims.

So, he traveled to Japan, where he was given the jawbone featured in the latest stduy from a Hiroshima victim. But the technology was not advanced enough, nor were there computers that could process the results in a precise manner. Making use of the instruments at hand, Mascarenhas presented evidence that the blast radiation aborbed by the jawbone sample could be observed at a meeting of the American Physical Society in 1973.

The jawbone was brought to Brazil, where it waited until science was ready for then-postdoctoral student Angela Kinoshita to continue Mascarenhas' research with co-author Oswaldo Baffa, her former professor at the University of São Paulo.

Kinoshita, who is now a professor at University of the Sacred Heart in Brazil, was able to use ESR to identify direct blast radiation in the jawbone from so-called background signal, which the press release explains as "a kind of noise...[that] may have resulted from the superheating of the material during the explosion."

To conduct their research, the team removed a small piece of the jawbone used in the previous study and then exposed it to radiation in a lab. This process is known as the additive dose method. Their result was similar to the dose found in physical objects taken from the site, including bricks and house tiles.

The scientists are currently looking into even more sensitive methodology, which they predict in the press release to be "about a thousand times more sensitive than spin resonance." They see their research becoming increasingly relevant in future events like in the case of a terrorism attack.

“Imagine someone in New York planting an ordinary bomb with a small amount of radioactive material stuck to the explosive,” Baffa tell Agência FAPESP. “Techniques like this can help identify who has been exposed to radioactive fallout and needs treatment.”

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