Demon core

Demon core
source
Name	Demon core
Caption	A re-creation of the core assembly used in the experiments.
Type	Subcritical mass
Origin	United States
Service	1945–1946
Used by	Manhattan Project
Designer	Los Alamos Laboratory
Weight	6.2 kg (13.7 lb)
Length	89 mm (3.5 in) diameter
Filling	Plutonium

Demon core. The Demon core was a spherical subcritical mass of plutonium that was involved in two separate criticality accidents at the Los Alamos Laboratory in 1945 and 1946, resulting in the acute radiation poisoning and subsequent deaths of two scientists. It was originally intended for use in a potential third nuclear weapon during World War II, but the end of the war with Japan following the atomic bombings of Hiroshima and Nagasaki rendered it surplus. The core became infamous for the fatal experiments conducted by physicists Harry Daghlian and Louis Slotin, who each suffered lethal doses of radiation while manually manipulating the assembly in separate incidents.

History and design

The core was manufactured at Los Alamos Laboratory as part of the wartime Manhattan Project. It consisted of a solid sphere of plutonium-gallium alloy, weighing 6.2 kilograms and measuring 3.5 inches in diameter, and was designed to be used in an implosion-type nuclear weapon. Following the surrender of Japan after the atomic bombings of Hiroshima and Nagasaki, the core was retained for research purposes at Los Alamos National Laboratory. Scientists, including members of the P-1 Division, began conducting experiments to determine the precise point of criticality by bringing the core to the edge of a self-sustaining nuclear chain reaction. These tests involved surrounding the sphere with neutron reflector materials, such as blocks of beryllium or a beryllium shell, to increase the efficiency of neutron reflection and push the assembly toward criticality.

Criticality accidents

The first accident occurred on August 21, 1945, when physicist Harry Daghlian was performing a solo experiment after hours. While stacking tungsten carbide bricks around the core as a neutron reflector, he accidentally dropped a brick onto the assembly, creating a supercritical configuration. Daghlian immediately disassembled the stack but received an estimated dose of 510 rems of neutron radiation. He was hospitalized at the Los Alamos Hospital and transferred to the Oak Ridge Hospital, where he died 25 days later from acute radiation sickness. The second, more famous accident took place on May 21, 1946, involving physicist Louis Slotin. During a demonstration for several colleagues, including Alvin C. Graves and Raemer Schreiber, Slotin used a screwdriver to manually lower a beryllium hemisphere over the core. The screwdriver slipped, allowing the hemispheres to fully enclose the core and instantly create a supercritical state, producing a bright blue flash of ionizing radiation and a surge of heat. Slotin received a lethal dose estimated at 2100 rems and died nine days later at the Los Alamos Hospital; several observers also suffered from varying degrees of radiation poisoning.

Aftermath and legacy

Following the second accident, all hands-on criticality experiments were immediately halted at Los Alamos National Laboratory. The core itself was later melted down and its material was recycled into other nuclear weapons as part of the postwar United States nuclear weapons program. The accidents led to the establishment of stringent new safety protocols for handling fissile material, emphasizing the use of remote manipulation and the implementation of the "one-point safe" design principle in nuclear weapons. Investigations by the United States Atomic Energy Commission resulted in significant changes to laboratory procedures, and the incidents became foundational case studies in the field of criticality safety. Memorials to Harry Daghlian and Louis Slotin were later established, and their deaths are commemorated in the history of the Manhattan Project National Historical Park.

In popular culture

The story of the Demon core and the accident involving Louis Slotin has been depicted in various films and other media. It served as a central plot element in the 1989 film *Fat Man and Little Boy*, where the character of Michael Merriman is based on Slotin. The core and the 1946 incident are also featured in the 2023 film *Oppenheimer*, directed by Christopher Nolan, which dramatizes the life of J. Robert Oppenheimer. Additionally, the events have been the subject of numerous documentary series, including episodes of Dark Matters: Twisted But True and Mysteries at the Museum, and have inspired storylines in television series such as The Blacklist. The term "Demon core" itself has entered popular lexicon as a cautionary symbol of scientific hubris and the dangers of nuclear technology.

Category:Manhattan Project Category:Nuclear accidents and incidents in the United States Category:Nuclear weapons of the United States Category:Los Alamos National Laboratory