Manhattan Project Scientists: Harry Daghlian

Harry Daghlian was among the promising young scientists who came to work at Los Alamos as part of the Manhattan Project. Harotune Krikor Daghlian Jr. (1921-1945), known as Harry, was raised in Illinois, attended MIT, and had graduated from Purdue University. He had not yet earned his doctorate in physics when he joined Project Y. Daghlian was assigned to work with Otto Frisch’s Criticality Assembly Group. He helped transport the plutonium core to the Trinity Site and was present for the test on July 16, 1945.

Just a few weeks later, on August 21, back at Los Alamos Daghlian was working alone at the remote Omega Site. His experiment involved building a neutron reflector using 9.7 pound (4.4 kg) tungsten carbide bricks stacked by hand around a spherical plutonium core. The objective was to reduce the mass required for the core to reach criticality. While moving the final brick, neutron sensors let him know that adding that brick would cause the system to go critical. As Daghlian attempted to withdraw it, he accidentally dropped the brick into the center of the assembly, and it went critical. He tried unsuccessfully to knock the brick away but had to remove some of the others to halt the reaction. The radiation he received led to severe radiation poisoning. Although Daghlian was given intensive medical care, he fell into a coma and died 25 days later. His was the first known death due to exposure to radiation in a laboratory setting.

Safety procedures for experiments were revised, including a requirement that at least two people be present. Discussions and designs were begun for creating remote-controlled test devices. Before they were in place a second criticality experiment accident occurred about a year later, May 21, 1946, causing the death of Daghlian’s co-worker Louis Slotin. He was using the same plutonium sphere, which came to be known as the “demon core.”

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