Nearly 80 years ago, a plutonium core that was nearly used to create an atomic bomb dropped on Japan resulted in the deaths of two physicists during dangerous experiments.
On August 15, 1945, after Emperor Hirohito unconditionally surrendered to the Allied forces, the third plutonium core prepared by scientists at the Los Alamos National Laboratory in the United States for the next attack was no longer needed for weapon production. At that time, nuclear scientists at the laboratory were allowed to keep the spherical mass made from a plutonium and gallium alloy, nicknamed “The Demon Core”.
Simulation of the experiment that caused Louis Slotin’s death. (Photo: Los Alamos Laboratory).
In a nuclear explosion, the radioactive core of the bomb is critical. The chain reaction begins and continues without further intervention. When the nuclear material reaches a supercritical threshold, the reaction accelerates. American scientists understood enough about the radioactive material to initiate the reaction in a bomb, but they wanted to gain a better understanding of the limits when the material transitions into a dangerously critical state.
One way to push the radioactive core to a critical state is to allow neutrons to bounce back into the core, making it increasingly unstable. The research team at Los Alamos conducted a series of experiments in which they built a neutron reflector around the radioactive core and monitored its state.
On the evening of August 21, 1945, physicist Harry Daghlian was alone in the laboratory, constructing a neutron reflector wall using tungsten bricks. At that time, the state of the core was highly unstable. When Daghlian placed a tungsten brick on top of the core, a powerful atomic reaction occurred, reaching supercritical levels, and Daghlian was exposed to a lethal dose of radiation. He died 25 days later.
However, Daghlian’s death did not deter the research team. Nine months later, they discovered another method to bring the Demon Core to the edge of criticality: by lowering a beryllium dome over the core. Louis Slotin, a Canadian physicist who had worked on the Manhattan Project, performed this operation in several previous experiments and took charge. He held the dome with one hand while using a screwdriver with the other to create a small gap to limit the number of neutrons hitting the core. On a day in May 1946, Slotin slipped, causing the dome to slam shut. The Demon Core once again reached supercritical levels, emitting gamma radiation towards Slotin and seven other scientists in the laboratory.
As the Demon Core released radiation, a blue light flashed in the room, the result of high-energy particles colliding with gas molecules, releasing a glowing stream of energy. The other scientists survived the accident, but Slotin, who was closest to the Demon Core, died from radiation exposure nine days later. This second death put an end to this dangerous research project.
After a period of storage, the Demon Core was used to create another weapon. Later, the U.S. military detonated the core in a nuclear test.
