The demon core was a sphere of plutonium that was involved in two fatal radiation accidents when scientists tested it as a fissile core of an early atomic bomb. It was manufactured by the Manhattan Project, the U.S. nuclear weapon development effort during World War II. It was a subcritical mass that weighed 6.2 kilograms (14 lb) and was 8.9 centimeters (3.5 in) in diameter.
The core was prepared for shipment to the Pacific Theater as part of the third nuclear weapon 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 with a tamper (layer of dense material surrounding the fissile material). Still, the core was accidentally put into a critical configuration. Physicists Harry Daghlian (in the first accident) and Louis Slotin (in the second accident) suffered acute radiation syndrome and died shortly afterward. At the same time, others present in the laboratory were also exposed. The core was melted down during the summer of 1946, and the material was recycled for use in other cores.
The demon core (like the core used in the bombing of Nagasaki) was, when assembled, a solid 6.2-kilogram (14 lb) sphere measuring 8.9 centimeters (3.5 in) in diameter. It consisted of three parts: two plutonium-gallium hemispheres and a 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. [1] [2]
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). [3] The metallurgists used a plutonium-gallium alloy, which stabilized the delta (δ) 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. [4]
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:
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. [3]
Marshall added an annotation, "It is not to be released on Japan without express authority from the President", as President Harry S. Truman was waiting to see the effects of the first two attacks. [3] 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. [3] 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. [5]
The core, assembled, was designed to be at "−5 cents". [6] 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. [7] These factors are not common in the environment; they are circumstances like 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 guarantee that the core was indeed close to the critical point by arranging such reflectors and seeing how much neutron reflection was required to approach supercriticality. [6]
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 10 to 12 feet (3 to 4 m) away. [8] 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. [9]
Name | Age at accident | Profession | Dose [8] : 20 | Aftermath |
---|---|---|---|---|
Haroutune "Harry" Krikor Daghlian Jr. | 24 | Physicist | 200 rad (2.0 Gy ) neutron 110 rad (1.1 Gy) gamma | Died 25 days after the accident of acute radiation syndrome, hematopoietic focus [8] : 22 |
Private Robert J. Hemmerly | 29 | Special Engineer Detachment 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 age 62 [8] : 9–11, 22 |
On May 21, 1946, [10] physicist Louis Slotin and seven other personnel were in a Los Alamos laboratory conducting another experiment to verify the closeness of the core to criticality by the positioning of neutron reflectors. Slotin, who was leaving Los Alamos, was showing the technique to Alvin C. Graves, who would use it in a final test before the Operation Crossroads nuclear 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 using a thumb hole at the polar point. As the reflectors were manually moved closer and farther away from each other, neutron detectors indicated the core's neutron multiplication rate. The experimenter needed to maintain a slight separation between the reflector halves to allow enough neutrons to escape from the core in order to stay below criticality. The standard protocol was to use shims between the halves, as allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion.
By Slotin's own unapproved protocol, the shims were not used. The top half of the reflector was resting directly on the bottom half at one point, while 180 degrees from this point a gap was maintained by the blade of a flat-tipped screwdriver in Slotin's hand. The size of the gap between the reflectors was changed by twisting the screwdriver. Slotin, who was given to bravado, [11] became the local expert, performing the test on almost a dozen occasions, often in his trademark blue jeans 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 the test in that manner. [12] Scientists referred to this flirting with the possibility of a nuclear chain reaction as "tickling the dragon's tail", based on a remark by physicist Richard Feynman, who compared the experiments to "tickling the tail of a sleeping dragon". [13] [14]
On the day of the accident, Slotin's screwdriver slipped outward a fraction of an inch while he was lowering the top reflector, allowing the reflector to fall into place around the core. Instantly, there was a flash of light; the core had become supercritical, releasing an intense burst of neutron radiation, the exposure of which was calculated based on the estimated half second between when the sphere closed to when Slotin removed the top reflector. [6] Slotin quickly twisted his wrist, flipping the top shell to the floor. [15] The position of Slotin's body over the apparatus shielded the others from much of the neutron radiation, but he received a lethal dose of 1,000 rad (10 Gy ) neutron and 114 rad (1.14 Gy) gamma radiation in less than a second. Slotin died nine days later from acute radiation poisoning.
Graves, the next nearest person to the core, was watching over Slotin's shoulder and was thus partially shielded by him. He received a high but non-lethal radiation dose. Graves was hospitalized for several weeks with severe radiation poisoning. [8] He died 19 years later, at age 55, of heart failure. While this may have been caused by Graves' exposure to radiation, the condition may have been hereditary as his father also died of heart failure. [16] [17] [18]
The second accident was reported by the Associated Press on May 26, 1946: "Four men injured through accidental exposure to radiation in the government's atomic laboratory here [Los Alamos] have been discharged from the hospital and 'immediate condition' of four others is satisfactory, the Army reported today. Dr. Norris E. Bradbury, project director, said the men were injured last Tuesday in what he described as an experiment with fissionable material." [19]
Later research was performed concerning the health of the men. An early report was published in 1951. A later report was compiled for the U.S. government and submitted in 1979. [8] A summary of its findings:
Name | Origin | Age at accident | Profession | Dose [8] | Aftermath | Ref. |
---|---|---|---|---|---|---|
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. | [10] |
Alvin C. Graves | Austin, Texas | 36 | 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. | [8] |
Samuel Allan Kline | Chicago, Illinois | 26 | Physics student, later patent attorney | Died in 2001 (55 years after the accident) at age 81; refused to participate with studies and was prevented from obtaining his own medical records from the incident. | [8] | |
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). | [8] |
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) at age 83. | [8] |
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 age 88. | [8] [15] |
Theodore Perlman | New Orleans, Louisiana [20] | 23 | Engineer | 7 rad (0.070 Gy) neutron 2 rad (0.020 Gy) gamma | "Alive and in good health and spirits" as of 1978; most likely died in June 1988 (42 years after the accident), in Livermore, California. | [8] [21] |
Private Patrick Joseph Cleary | New York City, New York | 21 | Security guard | 33 rad (0.33 Gy) neutron 9 rad (0.090 Gy) gamma | Sergeant 1st Class Cleary was killed in action on 3 September 1950 (4 years after the accident) while serving with the 8th Cavalry Regiment, US Army in the Korean War. | [8] [22] |
Two machinists, Paul Long and another, unidentified, in another part of the building, 20–25 ft (6–7.5 m) away, were not treated. [23]
After these incidents the core, originally known as "Rufus", was referred to as the "demon core". [3] [24] 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. [15]
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 in summer 1946 and the material recycled for use in other cores. [24]
"Fat Man" was the codename for the type of nuclear weapon the United States detonated over the Japanese city of Nagasaki on 9 August 1945. It was the second of the only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation marked the third nuclear explosion in history. The first one was built by scientists and engineers at Los Alamos Laboratory using plutonium manufactured at the Hanford Site and was dropped from the Boeing B-29 Superfortress Bockscar piloted by Major Charles Sweeney.
Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types:
A nuclear and radiation accident is defined by the International Atomic Energy Agency (IAEA) as "an event that has led to significant consequences to people, the environment or the facility." Examples include lethal effects to individuals, large radioactivity release to the environment, or a reactor core melt. The prime example of a "major nuclear accident" is one in which a reactor core is damaged and significant amounts of radioactive isotopes are released, such as in the Chernobyl disaster in 1986 and Fukushima nuclear disaster in 2011.
Louis Alexander Slotin was a Canadian physicist and chemist who took part in the Manhattan Project. Born and raised in the North End of Winnipeg, Manitoba, Slotin earned both his Bachelor of Science and Master of Science degrees from the University of Manitoba, before obtaining his doctorate in physical chemistry at King's College London in 1936. Afterwards, he joined the University of Chicago as a research associate to help design a cyclotron.
A criticality accident is an accidental uncontrolled nuclear fission chain reaction. It is sometimes referred to as a critical excursion, critical power excursion, divergent chain reaction, or simply critical. Any such event involves the unintended accumulation or arrangement of a critical mass of fissile material, for example enriched uranium or plutonium. Criticality accidents can release potentially fatal radiation doses if they occur in an unprotected environment.
Haroutune Krikor Daghlian Jr. was an American physicist with the Manhattan Project, which designed and produced the atomic bombs that were used in World War II. He accidentally irradiated himself on August 21, 1945, during a critical mass experiment at the remote Omega Site of the Los Alamos Laboratory in New Mexico and died 25 days later from the resultant radiation poisoning.
In nuclear engineering, prompt criticality describes a nuclear fission event in which criticality is achieved with prompt neutrons alone and does not rely on delayed neutrons. As a result, prompt supercriticality causes a much more rapid growth in the rate of energy release than other forms of criticality. Nuclear weapons are based on prompt criticality, while nuclear reactors rely on delayed neutrons or external neutrons to achieve criticality.
Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another. Although this is sometimes pictured as two sub-critical hemispheres driven together to make a supercritical sphere, typically a hollow projectile is shot onto a spike, which fills the hole in its center. Its name is a reference to the fact that it is shooting the material through an artillery barrel as if it were a projectile.
Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous.
Alvin Cushman Graves was an American nuclear physicist who served at the Manhattan Project's Metallurgical Laboratory and the Los Alamos Laboratory during World War II. After the war, he became the head of the J (Test) Division at Los Alamos and was director or assistant director of numerous nuclear weapons tests during the 1940s and 1950s. Graves was severely injured in the 1946 laboratory criticality accident in Los Alamos that killed Louis Slotin, but recovered.
In nuclear weapon design, the pit is the core of an implosion nuclear weapon, consisting of fissile material and any neutron reflector or tamper bonded to it. Some weapons tested during the 1950s used pits made with uranium-235 alone, or as a composite with plutonium. All-plutonium pits are the smallest in diameter and have been the standard since the early 1960s. The pit is named after the hard core found in stonefruit such as peaches and apricots.
A criticality accident occurred on December 30, 1958, at the Los Alamos National Laboratory in Los Alamos, New Mexico, in the United States. It is one of 60 known criticality events that have occurred globally outside the controlled conditions of a nuclear reactor or test, though it was the third such event that took place in 1958 after events on June 16 at the Y-12 Plant in Oak Ridge, Tennessee, and on October 15 at the Vinča Nuclear Institute in Vinča, Yugoslavia. The accident involved plutonium compounds dissolved in liquid chemical reagents; within 35 hours, it killed chemical operator Cecil Kelley by severe radiation poisoning.
Flattop is a benchmark critical assembly that is used to study the nuclear characteristics of uranium-233, uranium-235, and plutonium-239 in spherical geometries surrounded by a relatively thick natural uranium neutron reflector.
Raemer Edgar Schreiber was an American physicist from McMinnville, Oregon who served Los Alamos National Laboratory during World War II, participating in the development of the atomic bomb. He saw the first one detonated in the Trinity nuclear test in July 1945, and prepared the Fat Man bomb that was used in the bombing of Nagasaki. After the war, he served at Los Alamos as a group leader, and was involved in the design of the hydrogen bomb. In 1955, he became the head of its Nuclear Rocket Propulsion (N) Division, which developed the first nuclear-powered rockets. He served as deputy director of the laboratory from 1972 until his retirement in 1974.
Marshall Glecker Holloway was an American physicist who worked at the Los Alamos Laboratory during and after World War II. He was its representative, and the deputy scientific director, at the Operation Crossroads nuclear tests at Bikini Atoll in the Pacific in July 1946. Holloway became the head of the Laboratory's W Division, responsible for new weapons development. In September 1952 he was charged with designing, building and testing a thermonuclear weapon, popularly known as a hydrogen bomb. This culminated in the Ivy Mike test in November of that year.
The Los Alamos Laboratory, also known as Project Y, was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II. Its mission was to design and build the first atomic bombs. Robert Oppenheimer was its first director, serving from 1943 to December 1945, when he was succeeded by Norris Bradbury. In order to enable scientists to freely discuss their work while preserving security, the laboratory was located on the isolated Pajarito Plateau in Northern New Mexico. The wartime laboratory occupied buildings that had once been part of the Los Alamos Ranch School.
Dwight Smith Young was an American "carpenter, photographer, archaeologist, cook, meteorologist, poet and self-made physicist" who took part in the Manhattan Project. He was given the nickname "The Hermit of Pajarito Canyon" after making his home in an old log cabin in a remote canyon on the Los Alamos testing site from roughly 1946 to 1952.
Louis Henry Hempelmann Jr, was an American physician who was the director of the Health Group at the Manhattan Project's Los Alamos Laboratory during World War II. After the war he was involved in research into radiology. A paper he published in the New England Journal of Medicine in 1949 warned of the dangers of using fluoroscopes to measure the size of children's feet.
The Third Shot was the first of a series of American nuclear weapons intended for use against Japan in World War II, subsequent to the nuclear attacks on Hiroshima and Nagasaki. It was originally intended to be used on 19 August 1945, ten days after the bombing of Nagasaki. It was never used, as the surrender of Japan on 15 August brought the war to a close first.