Jakarta –
When the United States (US) dropped an atomic bomb on Hiroshima in August 1945, the Japanese city was engulfed in a powerful fireball that killed around 140 thousand people and vaporized the Earth and its infrastructure.
Seventy years later, scientists found debris from a nuclear explosion in the form of glass balls scattered along the coast of Motoujina, a small island in Hiroshima Bay.
The concrete and steel used to construct the buildings in Hiroshima seemed to have been shaken and burned at very hot temperatures, before cooling and falling back to Earth in round shapes, like glass beads.
Now, new analysis of the findings has revealed how they formed, namely through condensation inside a nuclear fireball.
The chemical and isotopic composition of the glass, analyzed by astrochemist Nathan Asset of the University of Paris Cité and colleagues, also shows similarities to primitive meteorites called chondrites that formed from interstellar dust and nebular gas in the early Solar System.
“The formation of Hiroshima glass through condensation implies that the glass may be analogous to the first condensate in the Solar System,” the researchers wrote in their paper, quoted from IFL Science.
These first condensates, or solids, also known as calcium-aluminum-rich inclusions (CAIs), also contain large amounts of the isotope oxygen-16 (16 O), a lighter form of oxygen with fewer neutrons than heavier varieties.
Scientists think that this 16O isotope may have been produced by UV light penetrating the clouds of interstellar dust gas where the first chondrites of the ancient Solar System formed, or it could have been produced through a specific mechanism when vaporized material condensed into a liquid before further solidifying.
Only a few laboratory experiments have tested this second explanation, so studying the wreckage of the Hiroshima explosion may provide new insights.
The team analyzed samples collected from the sandy beaches of Hiroshima Bay in 2015 by retired geologist Mario Wannier and his team. Analyzing 94 pieces of nuclear debris, Asset and colleagues identified four types of Hiroshima glass: melitic, anorthositic, soda-lime, and silica.
Hiroshima glass particles under a microscope, including melitic glass (A, B) and soda-lime glass (D). Photo: Nathan Asset
Chemically, silica glass looks the same as grains of quartz sand found on any beach, and soda-lime glass resembles industrially made glass. However, the four types of Hiroshima glass have strange oxygen and silicon isotope compositions that give researchers a new way to study how they might have formed.
To take a closer look, the team ran simulations that reconstructed the chemical makeup and physical conditions of nuclear explosions from previous studies, using those rough estimates to model possible condensation processes in the Hiroshima fireball.
Previous research estimated that the Hiroshima bomb exploded 580 meters above the city, too far from the surface to leave a crater. However, the temperature was so high, reaching 10 million degrees Celsius, inside the fireball itself and an estimated 6,287 °C at ground level, causing building materials to evaporate in a matter of seconds.
The team’s simulations reveal how the melitic fluid condenses from the gas cloud first, in a process known as fractionated condensation, followed by the anorthositic, soda-lime, and silica fluids. These droplets are then introduced into the glass when exposed to temperatures between 1,800 and 1,400 °C, depending on the composition.
A simulation sequence shows how material vaporized in the Hiroshima explosion condenses into droplets within seconds of the explosion. Photo: Nathan Asset
“Melitic glass is the first liquid to experience condensation and the last to cool, so it is the liquid that interacts the most with the material in the fireball,” explained Asset.
“This could explain why most inclusions are found in this type of glass,” he said.
Although the researchers are also interested in the prospect of the early Solar System through the lens of Hiroshima, they acknowledge that the pressure, temperature and gas mixture were very different between the Hiroshima fireball and the Sun’s accretion disk, where the chondrites first formed.
“Despite all these differences, the similarities between the Hiroshima and CAI glasses may point to similar processes, namely chemical reactions during condensation, to explain the similar 16 O enrichment,” the team concluded.
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2024-03-03 10:33:08
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