Today marks 76th anniversary of US atomic bomb dropped on Hiroshima, Japan

The Hiroshima government has long been outspoken about worldwide nuclear disarmament, and the community holds a Peace Ceremony every year to commemorate the loss of 140,000 lives in the 1945 attack by the US.

The immense destructive power of atomic weapons derives from a sudden release of energy produced by splitting the nuclei of the fissile elements making up the bombs’ core. The U.S. developed two types of atomic bombs during the Second World War.

The first, Little Boy, was a gun-type weapon with a uranium core. Little Boy was dropped on Hiroshima. The second weapon, dropped on Nagasaki, was called Fat Man and was an implosion-type device with a plutonium core.

Black shadows of humans and objects, like bicycles, were found scattered across the sidewalks and buildings of Hiroshima and Nagasaki, two of the largest cities in Japan, in the wake of the atomic blast detonated over each city on Aug. 6 and 9, 1945, respectively.

The photo above shows that the atomic bomb dropped on Hiroshima left shadows of people etched on sidewalks, an illusion created by bleaching the surface that was not obscured from the blast.

According to Dr. Michael Hartshorne, emeritus trustee of the National Museum of Nuclear Science and History in Albuquerque, New Mexico, and professor emeritus of radiology at the University of New Mexico School of Medicine, when each bomb exploded, the intense light and heat spread out from the point of implosion.

Objects and people in its path shielded objects behind them by absorbing the light and energy. The surrounding light bleached the concrete or stone around the “shadow.”

In other words, those eerie shadows are actually how the sidewalk or building looked, more or less, before the nuclear blast. It’s just that the rest of the surfaces were bleached, making the regularly colored area look like a dark shadow.

“The chain reaction occurs in a pattern of exponential growth that last[s] a millisecond or so,” said Alex Wellerstein, an assistant professor of science and technology studies at the Stevens Institute of Technology in New Jersey. “This reaction splits about a trillion, trillion atoms in that period of time before the reaction stop[s].”

The atomic weapons used in the 1945 attacks were fueled by uranium 235 and plutonium 239 and released a massive amount of heat and very shortwave, gamma radiation.

A year ago today, Hiroshima marked the 76th anniversary of the American atomic bomb dropped on Japan in the final days of World War II.

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