Harry K. Daghlian, Jr.
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Harry K. Daghlian, Jr., (1921 – September 15, 1945) was a physicist who died from performing a critical mass experiment at the remote Omega Site laboratory at the Manhattan Project Los Alamos laboratory in New Mexico, on August 21, 1945.
Daghlian was irradiated as a result of a criticality accident which occurred when he accidentally dropped a small tungsten carbide brick onto a 6.2 kg plutonium bomb core. This core, available at the close of World War II, was probably the core for the next intended atomic bomb to be used on Japan, never dropped.
In the experiment, the tungsten bricks were being slowly added around the core, being used as neutron reflectors, which serve to reduce the mass required for plutonium to be critical. Eventually, enough bricks would have been added to allow the assembly to go into a controlled critical nuclear reaction, as a miniature nuclear reactor. This last step was not to have been done by a scientist working alone, however, and Daghlian was breaking regulations by working on it late at night in the lab. Since the assembly was nearly in the critical state, the accidental addition of the last brick caused the reaction to go immediately into the prompt critical region of supercritical behavior.
The radiation event which accompanied prompt criticality was accompanied by a blue glow of ionization. Although no explosion occurred, the release of heat was nearly enough to melt the sphere, and probably a meltdown was averted only by the thermal expansion of the sphere and by Daghlian's immediate and reflexive move to knock the extra brick away with his hand.
Daghlian died less than a month later, from acute radiation sickness.
This incident was fictionalized in the 1995 book "Los Alamos" by Joseph Kanon.
On May 20, 2000, Daghlian was memorialized by the city of New London, Connecticut.
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