Tiny glassy particles that litter the beaches near Hiroshima in Japan are likely the resolidified remains of the city destroyed by a US atomic bomb on the morning of August 6, 1945, according to the results of a newly published study. The A-bomb dropped by the "Enola Gay" Boeing B-29 Superfortress bomber effectively levelled the city and caused the deaths of over 145,000 people from both the initial blast and subsequent radiation poisoning.
The debris first came to the attention of geologist Mario Wannier. Back in 2015, Wannier had been collecting beach samples from Japan's Motoujina Peninsula near the city of Hiroshima as part of a study assessing the health of marine ecosystems. As Wannier carried out his inspection of the debris, he noticed something strange among the ordinary fare of sand and single-cell organisms.
A significant number of tiny glassy spheres and other unusual structures measuring roughly 0.5 – 1 mm across were mixed in with the sand. The unexpected intruders were similar in appearance to particles that had been forged in the asteroid impact that triggered the extinction of all non-avian dinosaurs some 66 million years ago.
Following his initial discovery, Wannier returned to Japan to collect more samples. He discovered that the glassy debris accounted for 0.6 – 2.5 percent of the grains contained in each beach sample. All of the samples were collected within 4 – 7 miles (6.4 – 11.2 km) of Hiroshima, suggesting a connection between the cataclysmic 1945 atomic bomb air burst and the creation of the particles.
Wannier estimates that roughly 2,200 – 3,100 tons (1,996 – 2,812 tonnes) of the particles could be found in just 0.4 sq miles (1 sq km) of beach area, from the surface to a depth of four inches.
Pieces of debris were then analyzed using an electron microscope to narrow down their structure and makeup. The chemical composition of the particles was found to vary widely. Some were made entirely of iron, while others were rich in silicon and calcium. All of the materials were common in Hiroshima at the time of the 1945 explosion, including building materials such as concrete, stainless steel and marble.
Samples were then taken to Berkeley Lab in California, where they were probed using a technique called X-ray microdiffraction. This allowed the team to see ultra-fine details in the structure of the particles down to a millionth of a meter in scale. The presence of specific crystals within the tiny structures suggests that they were formed in an intensely hot environment with a temperature exceeding 3,300 °F (1,800 °C).
Based on their analysis, the scientists believe that the particles were created when material that once formed the city was swept up by the destructive force of the bomb. As they travelled with the rising fireball in the aftermath of the explosion, they mixed and bubbled, before cooling and condensing.
"This was the worst manmade event ever, by far," Wannier said. "In the surprise of finding these particles, the big question for me was: You have a city, and a minute later you have no city. There was the question of: 'Where is the city – where is the material?' It is a trove to have discovered these particles. It is an incredible story."
The researchers named the melt particles "Hiroshimaites," in reference to their likely origin, and hope that their work will encourage others to further study the debris left behind at Hiroshima and Nagasaki.
The findings have been published in the journal Anthropocene.
Source: Lawrence Berkeley National Lab
