Liveblogging the Cold War: August 21, 1945: Harry K. Daghlian, Jr.

Wikipedia: Harry K. Daghlian, Jr.: “Haroutune Krikor Daghlian, Jr… accidentally irradiated himself on August 21, 1945…

…during a critical mass experiment at the remote Omega Site facility at the Los Alamos Laboratory in New Mexico, resulting in his death 25 days later…. He accidentally dropped a tungsten carbide brick onto a 6.2 kg plutonium-gallium alloy bomb core. This core, subsequently nicknamed the ‘demon core’, also caused the death of another physicist, Louis Slotin, in an accident the following year, before it was used in the Operation Crossroads… tests….
In the experiment on August 21, 1945, Daghlian was attempting to build a neutron reflector by manually stacking a set of 4.4-kilogram (9.7 lb) tungsten carbide bricks in an incremental fashion around a plutonium core. The purpose of the neutron reflector was to reduce the mass required for the plutonium core to attain criticality. As he was moving the final brick over the assembly, neutron counters alerted Daghlian to the fact that the addition of this brick would render the system supercritical. As he withdrew his hand, he accidentally dropped the brick onto the center of the assembly. 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 supercritical region of neutronic behavior. This resulted in a criticality accident.
Daghlian reacted immediately after dropping the brick and attempted to knock off the brick without success; he was forced to partially disassemble the tungsten-carbide pile to halt the reaction. Daghlian was estimated to have received a dose of 510 rem (5.1 Sv) of neutron radiation, from a yield of 1016 fissions…. Despite intensive medical care, he developed symptoms of severe radiation poisoning, and died 25 days later after falling into a coma. He was the first known fatality caused by a criticality accident…

Originally published at www.bradford-delong.com.