The “Demon Core” refers to a plutonium-gallium sphere used in the Manhattan Project, the United States’ effort to develop atomic weapons. This spherical mass, weighing 6.2 kilograms and measuring 8.9 centimeters in diameter, was originally intended as the fissile core of a third atomic bomb. It consisted of two plutonium-gallium hemispheres and an anti-jet ring, designed to manage neutron flux during implosion.
Scientists at Los Alamos Laboratory used this core for criticality experiments, which aimed to understand how close the material was to initiating a self-sustaining nuclear chain reaction. These experiments helped determine the minimum amount of fissile material needed for a nuclear weapon. After Japan’s surrender in August 1945, the core was retained for further testing. This period of experimentation led to its ominous nickname due to two tragic accidents.
The Deadly Incidents
The Demon Core became infamous due to two criticality accidents that resulted in the deaths of two physicists. The first incident occurred on August 21, 1945, involving physicist Harry Daghlian at the Los Alamos Laboratory. Daghlian was conducting experiments to assess the core’s proximity to criticality by stacking neutron-reflective tungsten carbide bricks around it.
During the experiment, Daghlian accidentally dropped a brick directly onto the core, causing it to briefly become supercritical. This caused a burst of radiation and a visible blue flash, indicating a nuclear excursion. Despite quickly removing the brick, Daghlian received a lethal dose of radiation and succumbed to acute radiation syndrome 25 days later.
Less than a year later, on May 21, 1946, a second fatal accident transpired, this time involving physicist Louis Slotin. Slotin was demonstrating a criticality experiment known colloquially as “tickling the dragon’s tail,” which involved bringing two beryllium-coated hemispheres together around the core. He used a screwdriver to maintain a small gap between the hemispheres, preventing them from fully enclosing the core and reaching criticality.
During this demonstration, the screwdriver slipped, allowing the hemispheres to close completely around the Demon Core. This caused the core to immediately go supercritical, emitting a blinding blue flash and a surge of heat and radiation. Slotin instinctively knocked the hemispheres apart, stopping the reaction, but he had already received a massive, fatal dose of radiation. He died nine days later from acute radiation poisoning.
The Core’s Final Fate
Following the two criticality accidents, the Demon Core was deemed too hazardous for further direct use in criticality experiments. The risks associated with manual assembly and the loss of two scientists prompted a reevaluation of its future.
To prevent any further incidents, the core was dismantled. Its plutonium-gallium material was melted down during the summer of 1946. This process effectively destroyed the Demon Core as a distinct, assembled object. The recovered fissile material was then recycled and reused in other nuclear weapons programs. This marked the definitive end of the Demon Core’s existence.
Modern Nuclear Materials Safety and Handling
The incidents involving the Demon Core influenced the development of stringent safety protocols for handling fissile materials. Lessons learned from these early accidents highlighted the need for enhanced measures to prevent uncontrolled nuclear chain reactions. Today, the approach to nuclear materials prioritizes minimizing human proximity during experiments and operations.
Modern practices incorporate extensive use of remote handling equipment, allowing operators to manipulate radioactive materials from a safe distance, often behind substantial shielding. Regulatory bodies, such as the U.S. Department of Energy (DOE) and the Nuclear Regulatory Commission (NRC), establish frameworks for criticality safety. These frameworks dictate strict guidelines for the storage, transport, and experimental use of fissile materials.
Current safety standards include rigorous training, detailed procedural requirements, and multiple layers of engineering controls to prevent accidental criticality. Materials are stored in configurations that inherently prevent chain reactions, and transportation involves robust, certified containers. The aim is to ensure that incidents like those with the Demon Core are highly unlikely to occur.