Are Hiroshima and Nagasaki still radioactive? (2024)

Nuclear weapons are feared the world over due to their unparalleled destructive strength and their potential to sicken populations with radiation. These effects are known not just from thousands of test detonations, but also from the aftermath of the only time nuclear weapons have ever been used in warfare. In 1945, the U.S. bombed the Japanese cities of Hiroshima and Nagasaki on August 6 and August 9, respectively.

According to the Bulletin of the Atomic Scientists, the most credible estimates of the total death toll from both bombings range from 110,000 to 210,000 fatalities, including men, women, and children—most of who were civilians. These deaths were caused by both the initial destructive blast and fires as well as radiation poisoning.

Radiation poisoning is part of what makes nuclear weapons so destructive. Nuclear weapons explode because of a rapid nuclear reaction in which atoms are either split apart or fused together. This releases radioactive particles and harmful electromagnetic waves such as gamma rays that can harm people not just immediately after the explosion, but also for some time afterward in the form of residual radiation.

Residual radiation is partly the result of nuclear fallout—radioactive particles that are sent up into the atmosphere and fall back to Earth. Radioactive materials decay over a period of time known as a half-life. Depending on the material, this could be a fraction of a second or multiple decades.

Does this mean that the cities of Hiroshima and Nagasaki are still radioactive today? The answer is a definitive no.

After the Hiroshima and Nagasaki bombs, residual radiation was left behind but this declined rapidly. According to the city of Hiroshima local government website, research has indicated that 80 percent of residual radiation was emitted within 24 hours of the bombing.

According to the University of Columbia Center for Nuclear Studies, most nuclear fallout from the bombings was dispersed in the atmosphere or blown away by the wind. Since the bombs were detonated far above the ground there was little contamination in terms of neutron activation, which causes non-radioactive materials to become radioactive.

Peter Kuznick is director of the Nuclear Studies Institute and professor in the Department of History at American University. He told Newsweek: "'No' is really the correct answer. I think the scientific consensus is that most of the radiation would have dissipated quickly. It would be down to 1/1000th in 24 hours and 1/1,000,000 after a week."

However, Kuznick added that anecdotal evidence sometimes contradicts this, referring to the experience of Koko Kondo, a Hibakusha—a Japanese term referring to a survivor of the bombings.

Koko, who was 8 months old at the time, survived the bombing despite getting radiation poisoning and being less than a mile from the detonation. Her aunt and the aunt's young daughter came to the city to search for family three days later, "when experts now say radiation levels were greatly reduced," Kuznick said.

"Koko's young cousin, however, was not as lucky and died from the radiation poisoning," he added. "Experts contend that most of the radiation damage was done within the first minute of the detonation. I know scientists in Japan who challenge these findings and accuse the Radiation Effects Research Foundation of downplaying the effects of radiation, but no knowledgeable person believes there is any lingering health risk from living in Hiroshima or Nagasaki."

Today, both cities are bustling urban centers and radiation levels there are on par with the general levels of background radiation experienced the world over.