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| Fig. 1: A mock-up of the May 21, 1946 demon core accident. (Courtesy of the DOE. Source: Wikimedia Commons) |
After the bombing of Hiroshima and Nagasaki on August 6 and August 9 1945, a plutonium core for a third atomic bomb was being prepared at the Los Alamos National Lab. [1] Following the casting process, it was determined that the plutonium core would not be used for a third atomic bomb and it was held for scientific research. [2] This core would eventually lead to the death of two scientists and the injury of many more, some of the first closely studied deaths due to acute radiation syndrome, giving it the name demon core.
On August 21, 1945, less than one month after the casting of the plutonium core that would be known as the demon core, Harry Daghlian, a Los Alamos scientist, began one of a series of criticality assembly experiments using the plutonium core. [3] The experiment involved Daghlian surrounding the core with neutron reflecting material to force the core to a critical state. [2] In this case, the neutron reflecting material was a set of tungsten carbide bricks that were stacked around the sphere. While Daghlian was stacking the final brick, he noticed an irregular reading and attempted to quickly remove the final brick. In the process of moving the brick, Daghlian dropped it onto the assembly causing the core to go supercritical and emit a large amount of radiation. Daghlian died 24 days later due to acute radiation syndrome. [4]
Despite this fatal accident, experimentation with the demon core continued until a second fatal accident nine months later on May 21, 1946. This second accident began as an impromptu training demonstration orchestrated by Louis Slotin. [2,3] The demonstration was part of a second set of criticality experiments that used two beryllium hemispheres as the neutron reflecting material. The hemispheres were designed to completely surround the core, except for a small gap held open by a screwdriver, as shown in Fig. 1. When Slotin was moving the screwdriver, it slipped out from between the spheres resulting in the sphere achieving supercriticality for a second time in nine months. Slotin quickly removed the top hemisphere from the core, but it was too late to prevent him from receiving a fatal dose of radiation. Slotin died of acute radiation syndrome nine days later. [2]
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| Table1: Radiation doses received by the demon core accident victims. [2,4,5] († γ emission from 24Na.) |
Following the demon core accidents, detailed records were kept of the radiation doses received by the victims and their subsequent symptoms. To determine the radiation doses received by everyone in the room of each accident, the induced radioactivity of the sodium and phosphorus in their blood serum was measured and used to infer average body radiation doses, as shown in Table 1. [4] It is important to note that a measure of the induced radioactivity of sodium in the blood serum does not provide any information on the location on the body that received the highest dose of radiation and is an average body dose measurement. The moderately fast nature of the high energy particles that were emitted by the supercritical plutonium core were not able to pass through human tissue effectively. This, combined with the fact that radiation energy follows an inverse square law, decreasing in energy by the square of the distance from the source, resulted in body parts that were closer to the core receiving a significantly higher dose of radiation than those farther away. [1] For Daghlian and Slotin, this meant that their hands and arms received large doses of radiation, while their heads and legs received smaller doses. [4] Due to these high radiation doses to the hands and arms, both scientists experienced severe degradation of the skin on their hands and arms in addition to the symptoms of acute radiation syndrome. [4]
The progression of acute radiation syndrome is typically consistent between patients, and this was the case for Daghlian and Slotin. Both scientists immediately experienced symptoms like that of a bad stomach illness before feeling better for a few days. By the end of the first week after exposure, their symptoms rebounded and became significantly worse, with both of them experiencing high fever, weight loss, and severe gastrointestinal problems followed by death. [4]
In a study commissioned over thirty years after the demon core incidents, the health of the those that were present in the rooms with Daghlian and Slotin during the accident was reexamined. Of the eight people who survived past one year, four died due to health conditions that may be attributable to their radiation exposure in 1945 and 1946. [2] The other four people were either alive at the time of the study or died due to unrelated causes. Table 1 lists additional information about each survivor.
© Zev Granowitz. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute, and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] A. Wellerstein, "The Demon Core and the Strange Death of Louis Slotin," New Yorker, 21 May 16.
[2] L. H. Hempelmann, C. C. Lushbauch, and G. L.Voelz, "What Has Happened to the Survivors of the Early Los Alamos Nuclear Accidents," Los Alamos National Laboratory, LA-UR-79-2802, October 1979.
[3] M. W. Hubbell, The Fundamentals of Nuclear Power Generation: Questions and Answers (Authorhouse, 2011).
[4] L. H. Hempelmann and J. G. Hoffman, "Practical Aspects of Radiation Injury," Annu. Rev. Nucl. Sci. 3, 369 (1953).
[5] T. A. Pitterle, "Evaluated Neutron Cross Sections of Sodium-23 for the ENDF/BFile," Atomic Power Development Associates, APDA-217, June 1968.
