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

Los Alamos criticality accident, 1946

compiled by Wm. Robert Johnston
last modified 14 September 2005

Date: 21 May 1946

Location: Los Alamos Scientific Laboratory, New Mexico, USA

Type of event: criticality accident with plutonium metal assembly


An experimenter was demonstrating techniques to a group using a plutonium assembly. The assembly comprised two hemispheres of plutonium metal, total mass 6.2 kg (just short of bare critical mass). The experimenter had the two hemispheres together, separated by a screwdriver supporting the top hemisphere, when the assembly became supercritical. He separated the assembly within 0.5 seconds. The experimenter received a dose of 2100 rem, from which he died 9 days later. The other individuals in the room received doses of 360, 250, 160, 110, 65, 47, and 37 rem. The individual receiving the second highest dose, a woman, was the only other individual to develop radiation sickness.

Consequences: 1 fatality (2100 rem) and 1 injury (360 rem).


© 2004, 2005 by Wm. Robert Johnston.
Last modified 14 September 2005.
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