Hiroshima Beach: X-ray echoes of glassy fallout

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  • Published: May 15, 2019
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Hiroshima Beach: X-ray echoes of glassy fallout

Glassy view

Researchers collected and studied beach sands from locations near Hiroshima including Japan’s Miyajima Island, home to this torii gate, which at high tide is surrounded by water. The torii and associated Itsukushima Shinto Shrine, near the city of Hiroshima, are popular tourist attractions. The sand samples contained a unique collection of particles, including several that were studied at Berkeley Lab and UC Berkeley. (Credit: Ajay Suresh/Wikimedia Commons)

An X-ray study has proven that tiny glassy particles in the sand on Japan’s Motoujina Peninsula came from the fallout of the Hiroshima atomic bomb. Retired geologist Mario Wannier, who was studying tiny marine life spotted the unexpected in samples of sand from the beach there and hopes his discovery will raise awareness in the scientific community and beyond.

Wannier was comparing biological debris from different beaches with a view to assessing the local environmental health of marine ecosystems. He had been examining tiny sand particles under the microscope when he noticed some odd, glassy spheres, and other particles that were more akin to the debris left by a meteor impact rather than the pounding of the waves. The surprise finding had a perhaps obvious, the unimaginably devastating effect of the atomic bomb detonated over Hiroshima towards the end of World War II.

Destroyer of worlds

"I had seen hundreds of beach samples from Southeast Asia, and I can immediately distinguish mineral grains from the particles created by animals or plants, so that’s very easy,” Wannier explains. In the Motoujina sands, collected by colleague, Marc de Urreiztieta, Wannier saw the familiar traces of single-celled shelled organisms, foraminifera, but among this debris were countless extraneous particles. "They are generally aerodynamic, glassy, rounded," says Wannier and reminded him of the debris known to be present in geological samples from the K-T boundary which marked a mass extinction event thought to have been caused by a massive meteorite impact 66 million years ago. However, some of the glassy particles Wannier examined were unlike those from meteor impact. Indeed, some of the particles had a rubber-like composition and were coated with multiple layers of glass or silica. Some of the particles are wholly iron or steel, and so presumably came from building materials.

Moreover, the particles are both diverse and unique with up to a couple of dozen grams of such particles in every kilogram of sand sampled. The researchers estimate that in a single square kilometre to a depth of 10 centimetres there could be up to 3000 tonnes of these particles. Wannier sorted around 10000 of the particles into six different groups depending on their physical traits. The consistently high concentrations of this strange assortment of particles in beach sands collected up to 10 kilometres from the city of Hiroshima raised the obvious question as to whether they had been generated by the atomic blast on the morning of 6th August 1945. The bomb instantly killed more than 70000 with radiation effects afterwards bringing the total number of deaths to around 166000 by the end of the year.

X-ray microdiffraction

To get more detailed information about the particles than is possible with microscopic observation, the team recruited Rudy Wenk and his team who used Berkeley Lab’s Advanced Light Source to conduct X-ray microdiffraction experiments. The data revealed the presence of the minerals anorthite and mullite in some of the particles. The data also showed that the particles had to have formed at a temperature of at least 1800 degrees Celsius because of the characteristics of these two minerals taken together. It is worth noting that melt debris from the Trinity test site in New Mexico – where the first nuclear explosion was triggered – is very different, mainly because the debris is purely geological rather than the remnants of a devastated city and its buildings and roads.

Related Links

Anthropocene 2019, online: "Fallout melt debris and aerodynamically-shaped glasses in beach sands of Hiroshima Bay, Japan"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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