US bombing of Japanese cities of Hiroshima and Nagasaki in 1945 was the first and only use of nuclear weapons against civilian targets.
A series of studies subsequently began to measure the impact of fallout, both in terms of the radiation dose to which the victims were exposed and the impact of this exposure on DNA and health in general
Research conducted in the 1980s under the guidance of the physicist Sérgio Mascarenhas, full professor at the University of São Paulo (USP), Brazilian scientists have published an article in the journal PLOS ONE in which a method of accurate Measurement of the radiation dose of the bones of victims of nuclear bombs dropped on Japan is described.
The investigation was conducted during research by Angela Kinoshita, currently a professor at the Sagrado Coração University of Bauru, São Paulo State. Her supervisor was then Oswaldo Baffa, full professor at the Ribeirão Preto School of Philosophy, Science and Letters (FFCLRP-USP) of the University of São Paulo.
"We have used a technique called electron spin resonance spectroscopy for retrospective dosimetry, and there is currently renewed interest in this type of methodology due to the threat of terrorist attacks in countries like the United States," Baffa said.
Imagine, someone in New York is planting an ordinary bomb with a small amount of radioactive material stuck to the explosives. Techniques like these can help find out who has been exposed to radioactive fallout and needs to be treated. "
As Kinoshita explained, the study is unique in that it used samples of human tissue from victims of the bomb dropped on Hiroshima
There were serious doubts about the feasibility of using this method of determining the radiation dose contained in these Samples were deposited because of the processes involved in the episode, "she said. "The results confirm their feasibility and open up various possibilities for future research that could clarify details of the nuclear attack."
The equipment used for the investigation was purchased during a project co-ordinated by Baffa and supported by the São Paulo Research Foundation ̵
In the 1970s, when he arrived at São Carlos Physics Institute of the University of São Paulo (IFSC-USP) taught, discovered mascarene X-ray and gamma radiation made human bones weakly magnetic. The phenomenon known as paramagnetism occurs because the hydroxyapatite (crystalline calcium phosphate) absorbs carbon dioxide ions in the mineral part of the bone tissue, and when the sample is irradiated, the CO loses 2 electrons and becomes CO 2 -. This free radical serves as a marker for the radiation dose received by the material.
"I discovered that we could use this property for beam dosimetry and began to use this method in archaeological dating," recalls Mascaren.
His goal At that time, the age of the bones calculated in Sambaquis (heaps created by the original inhabitants of Brazil as rubble mountains, skeletons of prehistoric animals, human bones, stone or bone dishes and other wastes) was calculated on the basis of absorbed natural ones Radiation was found centuries ago through contact with elements such as thorium, which are present in the sand at the seashore.
Because of this research, he was invited to teach at Harvard University in the United States. However, before leaving for the United States, he decided to go to Japan to receive bone samples from the victims of the atomic bombs and test his method.
"They gave me a jawbone, and I decided to measure the radiation directly at Hiroshima University," he said. "I had to prove experimentally that my discovery was real."
Mascaren was able to show that a dosimetric signal could be obtained from the sample, even though the technology was still rudimentary and there were no computers that could process the results. The research was presented at the annual March meeting of the American Physical Society, where it made a strong impression. Mascarenhas brought the samples to Brazil, where they stay.
"There have been significant improvements in instrumentation to make it more sensitive over the past 40 years," Baffa said. "Now you see digitally processed data in spreadsheets and graphics on the computer screen, and basic physics has also evolved to simulate and manipulate the signal from the sample using computer techniques."
Thanks to these advances, he added that in the new study it was possible to separate the signal radiation dose, which is absorbed during the nuclear attack by the so-called background signal, a kind of noise researchers, who is suspected that it was caused by overheating of the material during the explosion.
"The background signal is a broad line that can be generated by different things and lacks a specific signature," said Baffa. "The dosimetric signal is spectral, and every free radical resonates at a certain point in the spectrum when it is exposed to a magnetic field."
To perform the measurements, the researchers removed millimeter-size Parts of the jawbone, in the previous study. The samples were re-irradiated in the laboratory using a technique called additive dosing.
"We added radiation to the material and measured the rise in the dosimetric signal," Baffa explained. "We then constructed a curve and extrapolated from it the initial dose, when the signal was probably zero, and this calibration method allowed us to measure different samples, since each bone and each part of the same bone has a different sensitivity to radiation, depending on its composition. "
Thanks to this combination of techniques they were able to measure a dose of about 9.46 Gray (Gy), which is high in Baffa's view. "About half of this dose or 5 Gy is fatal if the whole body is exposed to it," he said.
The value was comparable to the doses measured by other techniques used on non-biological samples, the luminescence of quartz grains in brick and roof tile fragments found at the bomb sites. According to the authors, they are also similar to the results of biological measurement techniques used as parameters in long-term studies using changes in survivor DNA.
"The measurement we have received in this recent study is more reliable and up to date than the preliminary result, but I currently evaluate a methodology that is about a thousand times more sensitive than spin resonance Months have news, "predicted Mascaren.
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