Opinion

by Hiromi Morita, Staff Writer

The rain that fell shortly after the atomic bombing was described by a character with the name of Yasuko, a niece of the protagonist in the book Black Rain, authored by Masuji Ibuse, as “something like splashes of mud” and “a sudden, black downpour.”

The Record of the Hiroshima A-bomb War Disaster, an account published in 1971, describes the situation as follows — “On the day of the bombing, huge tower-like cumulonimbus clouds formed all through the day. Sudden downpours occurred between around 9 a.m. and 4 p.m.”

There are three main possible causes of the clouds that produced the “black rain.” One were the clouds created by the fireball. After the atomic bomb exploded about 600 meters aboveground, a high-temperature fireball expanded and rose in the sky, gradually cooling and forming a mushroom cloud.

In addition, the shock waves reaching the ground sent dust and other particles up into the sky, creating clouds of dust. Finally, clouds were also created by the fires that completely incinerated the area within about two kilometers of the hypocenter.

All these clouds contained cesium generated by the fission of uranium, the raw material used in the Hiroshima atomic bomb, as well as dust and soot that contained radiation. Those particles are why the rain was black, and in some places the rain that fell had the consistency of mud.

People who were exposed to the rain have complained of health problems, but according to Nanao Kamata, professor emeritus at Hiroshima University who has conducted research over many years on the late effects of radiation exposure, “Exposure to residual radiation has not been adequately studied, and its effects on health have been neglected.”

When Mr. Kamata was director of a care facility for A-bomb survivors, he met a woman who developed four cancers when she was in her 80s. She had been living in the area of Takasu (now part of Hiroshima’s Nishi Ward), about 4.1 kilometers from the hypocenter, when the bomb was dropped. For about two weeks after the bombing, she consumed vegetables and water from the area around her home. An examination of her cancer tissue, which had been preserved, showed traces of alpha or beta rays from radioactive materials derived from uranium. For that reason, it is thought that her cancers might have been caused by internal exposure to radiation.

The black rain gives us insight into the widespread and long-lasting suffering experienced by people because of the atomic bombing.

(Originally published on June 11, 2024)