The Demon Core: A Story of Nuclear Aspiration and Tragic Consequences

Few accounts in the realm of atomic research are as captivating or cautionary as that of the demon core, a plutonium sphere crafted for one of the most destructive weapons ever devised. This narrative not only represents the pinnacle of nuclear ambition but also stands as a stark reminder of the human toll tied to such immense power.

Central to this tale are two scientists, Harry Daghlian and Louis Slotin, whose lives tragically intersected with the core's deadly nature. Their experiences highlight the delicate balance between pioneering scientific discovery and mortal peril.

The encounters of these two scientists with the demon core fundamentally transformed the trajectory of nuclear testing and safety measures, signifying a crucial turning point in the fields of nuclear physics and workplace safety.

What Is the Demon Core?

The demon core was a plutonium sphere, initially designed to serve as the core of the third atomic bomb the United States planned to deploy during World War II. As the war approached its conclusion, the U.S. launched two nuclear attacks on Japan — targeting Hiroshima and Nagasaki — aiming to hasten the end of the war.

Amid these historic events, plans were being made for a possible third attack. The plutonium core, which would later earn the ominous nickname "demon core," was intended to fuel this third nuclear device.

The purpose of its creation was evident: Should Japan refuse to surrender after the destruction of Hiroshima and Nagasaki, the U.S. was ready to deploy a third atomic bomb to compel their capitulation.

Yet, history unfolded differently. Japan's surrender following the two bombings halted the preparation and use of what could have been a third devastating strike. As a result, the demon core was never utilized as planned and remained at Los Alamos National Laboratory, shifting from a wartime weapon to a focus of scientific research.

Even in its inactive state, the core remained perilous due to its critical mass — a specific quantity of plutonium sufficient to maintain a nuclear fission chain reaction.

This latent ability to unleash immense energy marked the demon core as both an object of intrigue and dread, paving the way for incidents that highlighted the precarious balance between scientific progress and the value of human life.

Who Was Harry Daghlian?

Harry Daghlian, an American physicist, played a pivotal role in the United States' atomic research as part of the Manhattan Project. His tragic experience became a stark reminder of the hazards associated with handling radioactive materials.

During the summer of 1945, inside the Los Alamos laboratory, Daghlian conducted a crucial experiment aimed at exploring the limits of nuclear fission. His work involved assembling a neutron reflector around the demon core to gauge its proximity to criticality — the threshold where a nuclear chain reaction becomes self-sustaining.

Daghlian followed a meticulous process, carefully stacking layers of tungsten carbide bricks around the plutonium core. After completing five layers, he was on the verge of placing the final brick in the center when his monitoring equipment alerted him to the risk of the core becoming supercritical.

The setup was dangerously near achieving critical mass.

In response to the alert, Daghlian tried to remove the brick to stop the experiment and avert a critical reaction. Unfortunately, his hand slipped, causing the brick to fall onto the core. This accident initiated an immediate critical reaction, marked by a vivid blue flash and an intense wave of heat.

How Did Daghlian Lose His Life?

In that instant, Daghlian was exposed to a fatal dose of radiation from the plutonium, initiating a harrowing struggle with radiation sickness. Despite the dedicated efforts of medical staff, his health declined swiftly, and he succumbed to the illness 25 days later.

His untimely demise underscored the grave risks of the atomic era, acting as a stark warning about the immense power of the radioactive elements humanity had harnessed.

What Does 'Critical' Mean?

The word "critical" refers to a condition where a nuclear chain reaction becomes self-sustaining. This state is reached when fissile materials like plutonium or uranium attain a mass where each fission event releases enough neutrons to perpetuate a continuous series of reactions.

Reaching critical mass does not automatically lead to a nuclear explosion; instead, it signifies that the material has achieved a precise equilibrium between neutron generation and absorption. Under controlled environments, such as in nuclear reactors, maintaining criticality enables a stable energy output, which is harnessed for electricity production.

In contrast, for atomic weapons, exceeding criticality — entering a "supercritical" state — is intentionally pursued to trigger a swift, uncontrolled chain reaction, culminating in a catastrophic nuclear detonation.

Toying with the Sleeping Dragon

Even after Harry Daghlian's tragic death, researchers at Los Alamos persisted in their experiments with the core. Louis Slotin, a Canadian physicist renowned for his skill and confidence in managing radioactive materials, took up the challenge to push the limits of nuclear science.

Slotin was famous for performing a criticality experiment that involved pushing a plutonium core to the verge of criticality — essentially daring to approach the threshold of an uncontrolled nuclear chain reaction.

The experiment utilized two beryllium-coated metal hemispheres, which could be positioned near the demon core to reflect neutrons back into it, gradually nudging it toward criticality.

The pivotal moment in the procedure occurred when Slotin, using only a screwdriver, kept the two hemispheres slightly apart to prevent them from fully enclosing the plutonium core: a perilous technique famously referred to as "tickling the tail of the sleeping dragon."

On May 21, 1946, Slotin was showcasing this high-risk experiment to Alvin Graves, his designated successor, along with other scientists present. As Slotin conducted the experiment, a momentary lapse caused the metal hemispheres to close abruptly, instantly driving the core to criticality.

The room was suddenly filled with a blue flash of light and a surge of heat, indicating a sudden release of neutron radiation.

Although Slotin acted swiftly to separate the hemispheres and stop the reaction, the harm had already been inflicted. The others in the room survived with varying levels of radiation exposure, but Slotin was not as lucky. He received a lethal dose of radiation poisoning and passed away nine days later, becoming the demon core's second casualty.

How Many People Died From the Demon Core?

The demon core, a result of the Manhattan Project's ambitious pursuit of atomic energy, claimed the lives of two physicists. Harry Daghlian and Louis Slotin, the unfortunate victims, succumbed to fatal accidents that caused acute radiation syndrome, commonly referred to as radiation sickness.

The tragic deaths of Daghlian and Slotin underscored the grave dangers of working with radioactive materials and accelerated the establishment of stricter safety standards.

Following these accidents, improved safety measures, such as remote manipulation methods and rigorous criticality safety rules, were introduced to avoid similar tragedies.

While the demon core was directly responsible for two fatalities, its impact led to major progress in nuclear safety, protecting numerous lives in the years that followed during atomic research and energy generation.

Does the Demon Core Still Exist?

After its short but significant history, the demon core was melted down and repurposed into new cores for further testing.

After the second accident and Louis Slotin's death, the laboratory overhauled its approach to nuclear safety. Acknowledging the severe risks of hands-on criticality experiments, Los Alamos prohibited its scientists from ever engaging in such hazardous direct interactions again.

As part of these changes, criticality experiments at Los Alamos were carried out remotely, with scientists positioned approximately a quarter mile away from radioactive materials to guarantee their protection.

This transformation not only demonstrated a deeper understanding of the power and hazards of nuclear materials but also established a global standard for nuclear research. Since the U.S. has not deployed any additional nuclear weapons after Hiroshima and Nagasaki, the new cores derived from the demon core have remained unused.