Demon core

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The demon core was a 6.2-kilogram (14 lb), 3.5-inch-diameter (89 mm) subcritical mass of plutonium which went briefly super-critical in two separate accidents at the Los Alamos laboratory in 1945 and 1946. Each incident resulted in the acute radiation poisoning and subsequent death of a scientist. After these incidents the spherical plutonium pit was referred to as the "demon core."

The demon core was used in the first atomic bomb test to be conducted after World War II, five weeks after the second fatal accident. It performed normally and with the same explosive yield as the next core used in this set of two tests.

Manufacturing and early history[edit]

The third core, like the second core (the one dropped on Nagasaki), consisted of three parts: the two hemispheres and a ring, designed to keep neutron flux from "jetting" out of the joined surface between the hemispheres during implosion (the Trinity gadget's core, tested at Alamagordo in July, did not have such a ring).[1][2] The refined plutonium was shipped from the Hanford Site in Washington state to Los Alamos; an inventory document dated August 30 shows Los Alamos had expended "HS-1, 2, 3, 4; R-1" (the components of Gadget and Fat Man) and had in its possession "HS-5, 6; R-2", finished and in the hands of quality control. Material for "HS-7, R-3" were in the Los Alamos metallurgy section, being hot pressed and nickel plated, and would also be ready by September 5 (it's not certain whether this date allowed for the unmentioned "HS-8"'s fabrication to complete the fourth pit).[3]

On August 10, General Groves wrote to General Marshall, chief of staff of the Army, that:

The next bomb of the implosion type had been scheduled to be ready for delivery on the target on the first good weather after August 24th, 1945. We have gained 4 days in manufacture and expect to ship the final components from New Mexico on August 12th or 13th. Providing there are no unforeseen difficulties in manufacture, in transportation to the theatre or after arrival in the theatre, the bomb should be ready for delivery on the first suitable weather after August 17th or 18th.

Marshall added an annotation, "It is not to be released on Japan without express authority from the President", as President Truman was exerting his exclusive authority to order the drop, and was waiting to see the effects of the first two drops.[3] On the 13th the third bomb was scheduled: "[On] Thursday [August 16] it [the third bomb] would be in readiness; the 19th it would be dropped."[3] Japan surrendered on August 15, 1945. Caught by news of the war's end while in preparation for being couriered to Kirtland Field, the third core remained at Los Alamos.[4]

The core, assembled, was designed to be at "-5 cents", or 5 % percent below critical. In this state it takes but a small amount of additional criticality-enhancing factors to cause the core to become supercritical, and then prompt critical. Fortunately these factors are not common in the environment; they are items like the compression of the solid metallic core, which would eventually cause it to explode, the addition of more nuclear material or perhaps an external reflector which would reflect outbound neutrons back into the critical mass. The experiments described below, conducted at Los Alamos were designed to guarantee that the core was indeed close to the critical point by arranging such reflectors and seeing how much (or little) was required to enter super-criticality.

First incident[edit]

A re-creation of the 1945 incident. The sphere of plutonium is surrounded by neutron-reflecting tungsten carbide blocks.

On August 21, 1945, the plutonium core produced a burst of neutron radiation that led to Harry Daghlian's death. Daghlian, a physicist, made a mistake while working alone performing neutron reflection experiments on the core. The core was placed within a stack of neutron-reflective tungsten carbide bricks and the addition of each brick moved the assembly closer to criticality. While attempting to stack another brick around the assembly, Daghlian accidentally dropped it onto the core and thereby caused the core to go critical, a self-sustaining prompt critical chain reaction. Despite quick action in moving the brick off the assembly, Daghlian received a fatal dose of radiation. He died 25 days later from acute radiation poisoning.[5]

Name Origin Age at accident Profession Dose[6][7] Aftermath Reference
Haroutune "Harry" Krikor Daghlian, Jr. New London, CT 24 physicist 200 rad (2.0 Gy) neutron
110 rad (1.1 Gy) gamma
died 25 days after the accident of acute radiation syndrome, haematopoietic focus [8]
Pvt. Robert J. Hemmerly Whitehall, OH 29 Special Engineering Detachment (SED) guard 8 rad (0.080 Gy) neutron
0.1 rad (0.0010 Gy) gamma
died in 1978 (33 years after accident) of acute myelogenous leukemia at the age of 62 [8]

Second incident[edit]

A re-creation of the 1946 incident. The half-sphere is seen but core inside is not. The beryllium hemisphere is held up with a screwdriver.

On May 21, 1946,[9] physicist Louis Slotin and seven other Los Alamos personnel were in a Los Alamos laboratory conducting an experiment to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors. Slotin, who was leaving Los Alamos, was showing the technique to Alvin Graves, who would use it in a final test before the Crossroads tests scheduled a month later at Bikini Atoll. It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core via a thumb hole on the top. As the reflectors were manually moved closer and farther away from each other, scintillation counters measured the relative activity from the core. Allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion. Under Slotin's unapproved protocol, the only thing preventing this was the blade of a standard flathead screwdriver, manipulated by the scientist's other hand. Slotin, who was given to bravado, became the local expert, performing the test almost a dozen separate times, often in his trademark bluejeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be "dead within a year" if they continued performing it.[10]

On the day of the accident, Slotin's screwdriver slipped outward a fraction of an inch while lowering the top reflector, allowing the reflector to fall into place around the core. Instantly there was a flash of blue light and a wave of heat across Slotin's skin; the core had become supercritical, releasing an intense burst of neutron radiation estimated to have lasted about a half second.[11] He quickly twisted his wrist, flipping the top shell to the floor. The heating of the core and shells stopped the criticality within seconds of its initiation,[12] but Slotin's reaction prevented a recurrence and ended the accident. Slotin's body's positioning over the apparatus also shielded the others from much of the neutron radiation. He received a lethal dose of 1000 rads neutron/114 rads gamma[6] in under a second and died nine days later from acute radiation poisoning. The nearest person to Slotin, Alvin C. Graves, was watching over Slotin's shoulder and was thus partially shielded by him, received a high but non-lethal radiation dose.[6] Graves was hospitalized for several weeks with severe radiation poisoning, developed chronic neurological and vision problems as a result of the exposure,[6] and died 20 years later of a heart attack. This heart attack may have been caused by hidden complications from radiation exposure, but its cause could also have been genetic, as his father had died from the same cause.[13][14][15]

The personnel in the room were:

Name Origin Age at accident Profession Dose[6][7] Aftermath
Louis Alexander Slotin Winnipeg, Manitoba, Canada 35 physicist 1,000 rad (10 Gy) neutron
114 rad (1.14 Gy) gamma
died 9 days after the accident of acute radiation syndrome, gastrointestinal focus [9]
Alvin C. Graves Austin, Texas 34 physicist 166 rad (1.66 Gy) neutron
26 rad (0.26 Gy) gamma
died in 1965 (19 years after the accident) of myocardial infarction, with aggravating "compensated myxedema and cataracts", while skiing [6]
Stanley Allan Kline Chicago, Illinois physicist died in 2001 (55 years after the accident); refused to take part in studies [6]
Marion Edward Cieslicki Mt. Lebanon, Pennsylvania 23 physicist 12 rad (0.12 Gy) neutron
4 rad (0.040 Gy) gamma
died of acute myelocytic leukemia in 1965 (19 years after the accident) [6]
Dwight Smith Young Chicago, Illinois 54 photographer 51 rad (0.51 Gy) neutron
11 rad (0.11 Gy) gamma
died of aplastic anemia and bacterial endocarditis in 1975 (29 years after the accident) [6]
Raemer Edgar Schreiber McMinnville, Oregon 36 physicist 9 rad (0.090 Gy) neutron
3 rad (0.030 Gy) gamma
died of natural causes in 1998 (52 years after the accident), at the age of 88 [6][12]
Theodore Perlman Louisiana 23 engineer 7 rad (0.070 Gy) neutron
2 rad (0.020 Gy) gamma
"alive and in good health and spirits" as of 1978 [6]
Pvt. Patrick J. Cleary New York City 21 security guard 33 rad (0.33 Gy) neutron
9 rad (0.090 Gy) gamma
killed in combat in Korea in 1952 during the Korean War [6]

Two machinists in another part of the building were not treated: Paul Long and another, unidentified.

After Slotin's accident, hands-on criticality experiments were stopped, and remote-control machines were designed by Schreiber, one of the survivors, to perform such experiments with all personnel at a quarter mile distance.[12]

Demon core in use[edit]

Crossroads Able, a 23-kiloton air-deployed nuclear weapon detonated on July 1, 1946 using the "demon core".

The demon core was used in the Able detonation test of the Operation Crossroads series at Bikini Atoll on July 1, 1946.[16] Its yield was 23 kilotons of TNT (96 TJ), the same as the Crossroads/Baker core.

Cultural references[edit]

Paul Mullin wrote a play based on the last nine days of Slotin's life, named the Louis Slotin Sonata. It premiered in 1999 at Circle X Theatre in Los Angeles and went on to win the Los Angeles Drama Critics Circle Award for Outstanding World Premiere.[17]

Charles Stross refers to the Daghlian incident in his novel The Atrocity Archives, specifically in the included short novel by similar title.

The 1989 film Fat Man and Little Boy portrays, in a character named Michael Merriman (played by John Cusack), a fictional composite of Harry K. Daghlian and Louis Slotin. The character dies of radiation poisoning after two neutron-reflection hemispheres, which are separated by a screwdriver, connect accidentally.

Joseph Kanon recounts events surrounding the first criticality accident, "Tickling the tail of the sleeping dragon [...] Testing how far we can go," in his 1997 novel Los Alamos.[18]

See also[edit]


  1. ^ Wellerstein, Alex. "You don't know Fat Man". Restricted data blog. Retrieved 2014-04-04. 
  2. ^ Coster-Mullen, John (2010). Core Differences, from "Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man". Retrieved 2014-04-04.  An error: the illustration caption states the Fat Man core was plated in silver; it was plated in nickel, as the silver plating on the gadget core blistered. The disk in the drawings is a gold foil gasket.
  3. ^ a b c Wellerstein, Alex. "The third core's revenge". Restricted data blog. Retrieved 2014-04-04. 
  4. ^ Shreiber, Raemer; Rhodes, Richard. "Raemer Schreiber's Interview (1993)". Retrieved 28 May 2015. Raemer Schreiber being interviewed by Richard Rhodes
  5. ^ Miller, Richard L. (1991). Under the Cloud: The Decades of Nuclear Testing. The Woodlands, Texas: Two Sixty Press. pp. 68, 77. ISBN 0-02-921620-6. 
  6. ^ a b c d e f g h i j k l Hempelman, Louis Henry; Lushbaugh, Clarence C. and Voelz, George L. (1979-10-19). What Has Happened to the Survivors of the Early Los Alamos Nuclear Accidents? (PDF). Conference for Radiation Accident Preparedness. Oak Ridge: Los Alamos Scientific Laboratory. LA-UR-79-2802. Retrieved 5 January 2013.  Patient numbers in this document have been identified as: 1 - Daghlian, 2 - Hemmerly, 3 - Slotin, 4 - Graves, 5 - Kline, 6 - Young, 7 - Cleary, 8 - Cieleski, 9 - Schreiber, 10 - Perlman
  7. ^ a b 1978 estimates from Hempelman
  8. ^ a b Dion, Arnold. "Acute Radiation Sickness". 
  9. ^ a b A Review of Criticality Accidents, Sept 26, 1967, LANL
  10. ^ Welsome, Eileen (1999). The Plutonium Files (PDF). p. 184. ISBN 978-0-385-31402-2. Retrieved 18 November 2012. 
  11. ^ McLaughlin, Thomas P.; Monahan, Shean P.; Pruvost, Norman L.; Frolov, Vladimir V.; Ryazanov, Boris G.; Sviridov, Victor I. (May 2000). "A review of criticality incidents, 2000 Revision (LA-13638)" (PDF). p. 75. Retrieved 18 May 2014. 
  12. ^ a b c Larry Calloway. "Nuclear Naiveté" (PDF). Albuquerque Journal. 
  13. ^ Clifford T. Honicker (1989-11-19). "America's Radiation Victims: The Hidden Files". New York Times. p. 11. 
  14. ^ Alsop, Stewart; Robert E. Lapp (March 6, 1954). "The Strange Death of Louis Slotin" (PDF). Saturday Evening Post 226 (36). pp. 25ff. Retrieved 2014-04-03. 
  15. ^ Clifford T. Honicker (1989-11-19). "AMERICA'S RADIATION VICTIMS: The Hidden Files". The New York Times Magazine. Retrieved 2011-04-23. 
  16. ^ Miller 1991, p. 69.
  17. ^ Paul Mullins. "Louis Slotin Sonata". 
  18. ^ Christopher Lehmann-Haupt (May 15, 1997). "Seeking Light: Manhattan Project Murder Mystery". The New York Times. Retrieved 3 May 2011. 

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