Mystery material hidden for 80 years found at Hiroshima atomic bomb site

Scientists have identified a previously unknown metal alloy created during the atomic bomb explosion over Hiroshima in 1945. Researchers discovered the microscopic alloy inside tiny grains of radioactive fallout, known as “hiroshimaite,” collected from beach sands in Hiroshima Bay nearly 80 years after the bombing.

The team believes the alloy formed inside the nuclear fireball, where temperatures exceeded 7,000°C, instantly vaporising buildings, steel, glass and soil before the materials cooled within moments. Those extreme conditions produced a substance unlike any previously recorded by scientists.

The newly discovered alloy consists of iron, chromium, nickel, manganese, molybdenum, silicon and aluminium — elements commonly found in stainless steel. However, researchers found that the atoms combined into a completely new crystal structure as the fireball cooled at an extraordinary rate.

Scientists from the University of Florence made the discovery while analysing 34 glassy fallout particles recovered from Hiroshima Bay. Using advanced microscopes and X-ray analysis, they searched for unusual materials created during the explosion.

One metallic grain, measuring only a few thousandths of a millimetre across, stood out because its internal atomic structure did not match any known material. After comparing it with thousands of existing alloys, the researchers concluded they had identified a previously unknown multicomponent alloy.

Writing in the journal Science Advances, the researchers said: “We report the discovery of a previously unknown multicomponent alloy recovered from beach sands of Hiroshima Bay, formed during the August 6, 1945 atomic airburst.”

The scientists believe the finding suggests other unknown materials may still be hidden among microscopic debris left behind by the bombing. They added that studying such materials could improve understanding of how matter behaves under extreme temperatures and pressures.

The atomic bomb, codenamed “Little Boy,” was dropped on Hiroshima at 8:15 a.m. on August 6, 1945. It detonated approximately 1,900 feet above the city with an explosive force equivalent to about 15,000 tons of TNT. An estimated 60,000 to 80,000 people were killed instantly. By the end of 1945, the death toll had risen to about 140,000 as thousands more died from burns, injuries and radiation sickness.