Database of radiological incidents and related events--Johnston's Archive

Nagasaki atomic bombing, 1945

compiled by Wm. Robert Johnston
last modified 16 October 2005

Date: 9 August 1945

Location: Nagasaki, Japan

Type of event: combat use of nuclear weapon


Following prolonged strategic bombing of Japan during World War II, the United States conducted the second combat use of a nuclear weapon (following the attack on Hiroshima 3 days earlier). A B-29 bomber dropped a single Mk-II "Fat Man" atomic bomb over Nagasaki, estimated population 240,000. The Mk-II was an implosion design nuclear gravity bomb using plutonium. The primary target city, Kokura, had been covered by clouds, as was Nagasaki (the secondary target) when the bomber arrived. The bomb was dropped through a gap in the cloud cover over a point somewhat displaced from the city center. It detonated 500 meters over Nagasaki at 11:02 AM local time with a yield estimated at 21 kilotons. The airburst height was selected to maximize the extent of prompt effects and to minimize residual radiation (fallout). Individuals at ground zero received combined gamma and neutron doses of perhaps 200,000 rad, although flash and blast would have been immediately fatal. The thermal flash produced fires which swept through much of the city. Flash, blast, and prompt radiation killed most people within 1.5 km of ground zero; immediate fatalities were generally from flash and blast injuries, with many otherwise injured and uninjured dying of fatal prompt radiation doses over the following weeks and months. Small numbers of people were injured by residual radiations (neutron-induced radioactivity and residual material from the weapon).

On the day of the bombing, an estimated 263,000 were in Nagasaki, including 240,000 Japanese residents, 10,000 Korean residents, 2,500 conscripted Korean workers, 9,000 Japanese soldiers, 600 conscripted Chinese workers, and 400 prisoners of war. Casualty figures are uncertain, despite many surveys (some figures presented here are extrapolated from partial surveys). Estimated fatalities are 70,000 (various published estimates range from 22,000 to 74,000), including 2,000 Koreans and at least 100 POWs. After 1950, deaths attributed to radiation include about 35 leukaemia deaths, 175 other cancer deaths, and 85 non-cancer deaths. New cases of leukaemia peaked in 1952.

Those injured in the bombing numbered 74,900 (through December 1945). Thousands of injured survivors were transported by train and other means to neighboring cities. From 10,000 to 30,000 are registered as having entered Nagasaki shortly after the bombing. Survivor registries include 1,600 individuals exposed in utero.

Japan surrendered three days after the bombing, ending World War II. Portions of Nagasaki with little or no damage were continously inhabited, and the city was rebuilt. Nagasaki reattained its pre-attack population by 1954 and had a population of 441,000 in 1992.

Consequences: Estimated 70,000 fatalities (of which perhaps 30,000 are related to ionizing radiation injuries) and 75,000 injuries.


© 2004, 2005 by Wm. Robert Johnston.
Last modified 16 October 2005.
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