Demon core

blocks acting as neutron reflectors. The demon core was a sphere of plutonium–gallium alloy that was involved in two fatal radiation accidents when scientists tested it as a fissile core of an early atomic bomb. It was manufactured in 1945 by the Manhattan Project, the U.S. nuclear weapon development effort during World War II. It was a subcritical mass that weighed and was in diameter. The core was prepared for shipment to the Pacific Theater as part of the third nuclear weapon intended to be dropped on Japan, but when Japan surrendered, the core was retained for testing and potential later use in the case of another conflict. The two criticality accidents occurred at the Los Alamos Laboratory in New Mexico on August 21, 1945, and May 21, 1946. In both cases, an experiment was intended to demonstrate how close the core was to criticality, using a neutron-reflective tamper (layer of dense material surrounding the fissile material). In both accidents, the core was accidentally put into a critical configuration. Physicists Harry Daghlian (in the first accident) and Louis Slotin (in the second accident) both suffered acute radiation syndrome and died shortly afterward. Others present in the laboratory were also exposed to radiation during the accidents. The core was melted down during the summer of 1946, and the material was recycled for use in other cores.

blocks acting as neutron reflectors.]] The demon core was a sphere of plutonium–gallium alloy that was involved in two fatal radiation accidents when scientists tested it as a fissile core of an early atomic bomb. It was manufactured in 1945 by the Manhattan Project, the U.S. nuclear weapon development effort during World War II. It was a subcritical mass that weighed and was in diameter. The core was prepared for shipment to the Pacific Theater as part of the third nuclear weapon intended to be dropped on Japan, but when Japan surrendered, the core was retained for testing and potential later use in the case of another conflict. The two criticality accidents occurred at the Los Alamos Laboratory in New Mexico on August 21, 1945, and May 21, 1946. In both cases, an experiment was intended to demonstrate how close the core was to criticality, using a neutron-reflective tamper (layer of dense material surrounding the fissile material). In both accidents, the core was accidentally put into a critical configuration. Physicists Harry Daghlian (in the first accident) and Louis Slotin (in the second accident) both suffered acute radiation syndrome and died shortly afterward. Others present in the laboratory were also exposed to radiation during the accidents. The core was melted down during the summer of 1946, and the material was recycled for use in other cores.

Manufacturing and early history

The demon core was a solid softball-sized sphere measuring in diameter; it was similar to the core used in the bombing of Nagasaki. It consisted of three parts made of plutonium–gallium: two hemispheres and an anti-jet ring, designed to keep neutron flux from "jetting" out of the joined surface between the hemispheres during implosion. The core of the device used in the Trinity Test at the Alamogordo Bombing and Gunnery Range in July did not have such a ring. . Both died following supercritical accidents involving the "demon core".]] The refined plutonium was shipped from the Hanford Site in Washington to the Los Alamos Laboratory; an inventory document dated August 30 shows Los Alamos had expended "HS-1, 2, 3, 4; R-1" (the components of the Trinity and Nagasaki bombs) and had in its possession "HS-5, 6; R-2", finished and in the hands of quality control. Material for "HS-7, R-3" was in the Los Alamos metallurgy section and would also be ready by September 5 (it is not certain whether this date allowed for the unmentioned "HS-8 s fabrication to complete the fourth core). The metallurgists used a plutonium–gallium alloy, which stabilized the delta ( ) phase allotrope of plutonium so it could be hot pressed into the desired spherical shape. As plutonium was found to corrode readily, the sphere was then coated with nickel. On August 10, Major General Leslie R. Groves Jr., wrote to General of the Army George C. Marshall, the Chief of Staff of the United States Army, to inform him that: Marshall added an annotation, "It is not to be released on Japan without express authority from the President", on President Harry S. Truman's orders. On August 13, the third bomb was scheduled. It was anticipated that it would be ready by August 16 to be dropped on August 19. This was pre-empted by Japan's surrender on August 15, 1945, while preparations were still being made for it to be couriered to Kirtland Field. The third core remained at Los Alamos.

First incident

The core, once assembled, was designed to be at "−5 cents". In this state, there is only a small safety margin against extraneous factors that might increase reactivity, causing the core to become supercritical, and then prompt critical, a brief state of rapid energy increase. These factors are not common in the environment; they are only likely to occur under conditions such as the compression of the solid metallic core (which would eventually be the method used to explode the bomb), the addition of more nuclear material, or provision of an external reflector which would reflect outbound neutrons back into the core. The experiments conducted at Los Alamos leading to the two fatal accidents were designed to see how much neutron reflection was required to approach supercriticality, and included arranging such reflectors in a way that would guarantee that the core was indeed close to the critical point. On August 21, 1945, the plutonium core produced a burst of neutron radiation that resulted in physicist Harry Daghlian's death. Daghlian made a mistake while performing neutron reflector experiments on the core. He was working alone; a security guard, Private Robert J. Hemmerly, was seated at a desk away. The core was placed within a stack of neutron-reflective tungsten carbide bricks, and the addition of each brick made 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 well into supercriticality, a self-sustaining critical chain reaction. He quickly moved the brick off the assembly, but he received a fatal dose of radiation. He died 25 days later from acute radiation poisoning.

Second incident

Medical studies

Later research was performed concerning the health of the men. An early report was published in 1951¹. A later report was compiled for the U.S. government and submitted in 1979. A summary of its findings: Two machinists, Paul Long and another, unidentified, in another part of the building, away, were not treated. After these incidents, the core, originally known as "Rufus", was referred to as the "demon core". Hands-on criticality experiments were stopped, and remote-control machines and TV cameras were designed by Schreiber, one of the survivors, to perform such experiments with all personnel at a quarter-mile distance.

Planned uses and fate of the core

The demon core was intended for use in the Operation Crossroads nuclear tests, but after the second criticality accident, time was needed for its radioactivity to decrease and for it to be re-evaluated for the effects of the fission products it held, some of which were very neutron poisonous to the desired level of fission. The next two cores were shipped for use in Able and Baker, and the demon core was scheduled to be shipped later for the third test of the series, provisionally named Charlie, but that test was canceled because of the unexpected level of radioactivity resulting from the underwater Baker test and the inability to decontaminate the target warships. The core was melted down during the summer of 1946, and the material was recycled for use in other cores.

See also

Cecil Kelley criticality accident

References

External links

Text derived from https://en.wikipedia.org/w/index.php?oldid=1377915236 under CC BY-SA 4.0; modifications have been made.