With more than 70 years having passed since Hiroshima and Nagasaki were bombed in World War II, researchers have determined the amount of radiation Hiroshima’s victims were exposed to when the United States bombed the city on August 6, 1945.
According to a report from Science Daily, the research kicked off several decades ago and was originally led by University of Sao Paulo professor Sergio Mascarenhas, then later led by Universidade do Sagrado Coracao professor Angela Kinoshita as part of her postdoctoral research. The findings were based on a phenomenon Mascarenhas observed in the 1970s, when he found that X-ray and gamma ray irradiation caused human bones to become “weakly magnetic,” resulting in what is now known as paramagnetism.
While Mascarenhas originally planned to use his discovery to determine the age of bones of Brazil’s earliest inhabitants based on the accumulated natural radiation they had absorbed over time, he also obtained a jawbone belonging to a victim of the Hiroshima bombing to prove that his discovery was “genuine.” This involved measuring the amount of radiation the bones had absorbed during the catastrophic event, based on dosimetric signals obtained through the paramagnetism phenomenon.
Decades later, the researchers behind the new study, which was published in PLOS One, used modern methodologies, including electronic spin resonance (ESR) spectroscopy, to get a more specific estimate of radiation levels. Science Daily wrote that the researchers used the jawbone previously tested by Mascarenhas, removing tiny pieces, then irradiating the samples with a technique known as the additive dose method.
Once the analysis was complete, the researchers determined that the Hiroshima victim’s jawbone was exposed to about 9.46 grays (Gy) worth of radiation. According to study co-author and University of Sao Paulo professor Oswaldo Baffa, this is a very high figure, as it only takes about 5 Gy of radiation to kill a human, assuming their entire body is exposed. Furthermore, it was also found that the figure was similar to the radiation levels found in brick and roof tile fragments from the Hiroshima and Nagasaki bomb sites.