When each atomic bomb detonates, intense heat and light radiate from the blast site, “bleaching” areas left uncovered.
The Haunting Shadows of Hiroshima and Nagasaki
The eerie black shadows of people and objects, such as bicycles, appeared sporadically on sidewalks and structures in Hiroshima and Nagasaki, two of Japan’s largest cities, following the US atomic bombings on August 6 and 9, 1945, respectively. These shadows may have encapsulated the final moments of each person, akin to the ashes of victims in the ancient volcanic eruption at Pompeii. So how were these shadows formed?
When each bomb detonates, intense heat and light radiate from the blast site, according to Dr. Michael Hartshorne, an expert at the National Museum of Nuclear History and Science in New Mexico. Humans and objects shielded structures behind them by absorbing light and energy. The light bleached the concrete or stone surrounding these shadows.
In other words, the peculiar black shadows on sidewalks and buildings are essentially the silhouettes of those structures before the nuclear blast. As the rest of the surface was bleached, the normally colored area appeared black.
The immensely powerful energy released in the atomic bomb blast is the result of the nuclear fission process. According to the Atomic Heritage Foundation (AHF), fission occurs when a neutron collides with the nucleus of a heavy atom, such as uranium-235 or plutonium-239. Upon collision, the nucleus of that element breaks apart, releasing a significant amount of energy. The initial collision triggers a chain reaction that continues until all the original material is depleted.
“The chain reaction occurs in an exponentially growing manner, lasting about 1 millisecond. This reaction splits about one trillion atoms in that time,” said Alex Wellerstein, associate professor of science and technology studies at Stevens Institute of Technology.
The energy is transmitted in the form of photon waves with different wavelengths, including long waves like radio waves and short waves like X-rays and gamma rays. Between long and short waves are visible wavelengths containing energy perceived by the human eye as colors. However, unlike long-wave energy, gamma radiation is harmful to the human body because it can penetrate clothing and skin, causing ionization or electron loss, damaging tissue and DNA.
The gamma radiation emitted by atomic bombs also propagates as thermal energy, reaching temperatures of over 5,500 degrees Celsius. Upon striking an object such as a bicycle or a human, the energy is absorbed, creating the phenomenon of a black shadow amidst the bleached area surrounding it.
The atomic weapons used in the 1945 attacks employed uranium-235 and plutonium-239, releasing gamma radiation and immense heat. In reality, there may initially have been more shadows, but most were destroyed by heat and subsequent shockwaves, Hartshorne noted.
Over time, the long-term consequences of radiation from these bombs have raised significant questions about their use. Many shadows imprinted on stone surfaces have vanished due to weathering and erosion by wind and water. Some shadow imprints have been removed and preserved in the Hiroshima Peace Memorial Museum for future generations to observe and reflect upon.