Harry K. Daghlian, Jr.

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Harry K. Daghlian, Jr.
Born Haroutune Krikor Daghlian, Jr.
(1921-05-04)May 4, 1921
Waterbury, Connecticut
Died September 15, 1945(1945-09-15) (aged 24)
Los Alamos, New Mexico
Cause of death Radiation poisoning
Education Bachelor of Science
Alma mater Purdue University
Occupation Physicist
Home town New London, Connecticut

Haroutune Krikor Daghlian, Jr. (May 4, 1921 – September 15, 1945) was an Armenian American physicist with the Manhattan Project who accidentally irradiated himself on August 21, 1945, during a critical mass experiment at the remote Omega Site facility at Los Alamos National Laboratory in New Mexico, resulting in his death 25 days later.

Daghlian was irradiated as a result of a criticality accident that occurred when he accidentally dropped a tungsten carbide brick onto a 6.2 kg delta phase plutonium bomb core. This core, available at the close of World War II and later nicknamed the "demon core", also resulted in the death of Louis Slotin in a similar accident, and was used in the Able detonation, during the Crossroads series of nuclear weapon testing.

Early life[edit]

Daghlian was the first of three children born to Margaret Rose Currie and Haroutune Krikor Daghlian. Soon after his birth in Waterbury, Connecticut, the family moved across state to the coastal town of New London. He was educated at Harbor Elementary School, where he played violin in the school orchestra, and at Bulkeley High School. In 1938, at the age of 17, he entered the Massachusetts Institute of Technology, intending to study mathematics, but became interested in physics, particularly particle physics, which was then emerging as an exciting new field. This led him to transfer to the West Lafayette, Indiana, campus of Purdue University, from which he obtained a bachelor of Science degree in 1942. He then commenced work on his doctorate. In 1944, he joined Otto Frisch's Critical Assembly Group at Los Alamos.[1]

Criticality accident[edit]

The sphere of plutonium surrounded by neutron-reflecting tungsten carbide blocks in a re-enactment of Harry Daghlian's 1945 experiment.[2]

In the experiment on August 21, 1945, Daghlian was attempting to build a neutron reflector by manually stacking a set of 4.4 kg 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.[2]

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 superprompt critical region of neutronic behavior. This resulted in a criticality accident.[2]

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.[3] Daghlian was estimated to have received a dose of 510 rem (5.1 Sv) of neutron radiation, from a yield of 1016 fissions.[2] Despite intensive medical care, he soon developed symptoms of severe radiation poisoning and died 25 days later after falling into a coma.[1][3] He was the first known fatality caused by a criticality accident.[4]


As a result of the incident, safety regulations for the project were scrutinized and revised. A special committee was established to review any similar experiments and recommend appropriate safety procedures. These procedures included needing a minimum of two people involved in such an experiment; at least two instruments monitoring neutron intensities, each with audible alerts; and a prepared plan for operating methods and any contingencies which may occur during an experiment. Additionally, discussions and designs for remote-controlled test devices were initiated, which eventually led to the creation of the Godiva device.[5] These changes did not prevent another criticality accident at Los Alamos: Louis Slotin was killed in 1946 while performing criticality tests on the same core that killed Daghlian.[2] Daghlian was memorialized on May 20, 2000, by the city of New London, with the erection of a memorial stone and flagpole in Calkins Park.[1]

See also[edit]


  1. ^ a b c Dion, Arnold S., Harry Daghlian: America's first peacetime atom bomb fatality, retrieved April 13, 2010 
  2. ^ a b c d e McLaughlin, Thomas P.; Monahan, Shean P.; Pruvost, Norman L.; Frolov, Vladimir V.; Ryazanov, Boris G.; Sviridov, Victor I. (May 2000), A Review of Criticality Accidents (PDF), Los Alamos, New Mexico: Los Alamos National Laboratory, pp. 74–75, LA-13638, retrieved April 21, 2010 
  3. ^ a b Miller, Richard L. (1991). Under the Cloud: The Decades of Nuclear Testing. The Woodlands, Texas: Two Sixty Press. pp. 68, 69, 77. ISBN 0-02-921620-6. 
  4. ^ Nuclear industry. Atomic Industrial Forum. 1959. p. 29. ISBN 9781463424411. Retrieved 19 August 2012. 
  5. ^ Hayes, Daniel F. (August 1956), A Summary of Accidents and Incidents Involving Radiation in Atomic Energy Activities, June 1945 through December 1955 (PDF), Oak Ridge, Tennessee: U.S. Atomic Energy Commission, pp. 2–3, TID-5360, retrieved April 12, 2010