The Demon Core a story for Halloween

31/10/2019 | Posted by Tony Hitchens

A suitably scary (and true) story for Halloween

During the Manhattan Project – the top-secret project to build an atomic bomb – four bomb cores were produced. These cores provided the explosive component of the atomic weapons by fission through reaching critical mass.

This story concerns the last of these cores that remained after the detonation of the Trinity weapon, and the two used in the bombing of Hiroshima and Nagasaki. The core itself was composed of a fist-sized ball of plutonium. The Manhattan Project scientists, in an effort to better understand these materials, wished to understand the mass and composition of isotopes required to generate a critical chain reaction if used in an atomic bomb.

The demon core

The ball of plutonium was surrounded with material that reflected neutrons produced by the plutonium back into the sphere, liberating more neutrons which in turn would also be reflected back.

The work was dangerous and delicate.

The first accident occurred on the 21st of August 1945. Physicist Harry Daghlian was using bricks of tungsten carbide to reflect neutrons into the core. While moving one brick into place the level of radiation increased sharply, and so he started to move the brick away again. The brick was dropped onto the core by accident, which immediately brought it to a state of supercriticality, and it began emitting huge amounts of radiation. Harry worked to removes the bricks to reduce the activity, but he had already received a fatal dose of radiation and died 25 days later from the exposure. The burst of neutron radiation also reached the security guard in the room, 29-year-old Private Robert Hemmerly, who was 3 to 4 metres away from the experiment. Although Hemmerly did not die until he was 62, the cause of death was radiation-related leukaemia.

The core earned its nickname, the Demon Core, after the second accident nearly a year later in May 1946.

Physicist Louis Slotin was investigating the core before it’s intended use in the Operation Crossroads nuclear tests at Bikini Atoll. In these tests, the neutrons emitted from the core were deflected by two surrounding hemispheres of beryllium. If the two halves of beryllium were allowed to fully close around the core, it would become supercritical releasing a wave of radiation. The safety protocol required spacers to be placed between the two halves so they could never meet, however, Slotin omitted them and used a screwdriver instead to raise and lower the upper sphere. The second accident occurred when during one test the screwdriver slipped and the two halves came into full contact. There was a blue flash of radiation before Slotin moved the two halves apart. The radiation burst lasted half a second. Slotin asked everyone in the room to use chalk to mark their position and he calculated the dose they would receive, knowing he would have received a fatal dose (he had taken a dose of greater than 1000 rad). He died nine days later from radiation poisoning. It is likely that Slotin’s body acted as a shield for the other people in the room, but they still suffered. Alvin C. Graves, immediately behind Slotin during the accident, developed cataracts and thyroid problems and died 19 years later of a heart attack which may have been caused by complications from the exposure. Others in the room were also exposed, but none receiving a lethal dose as they were further away from the core (radiation exposure drops off sharply with distance). While some of the others present during the accident died of complications involving blood leukaemia and disorders which could be linked to their exposures, they lived for several decades following the incident.

Where is the Demon Core now

The core was eventually melted down and used for other atomic bomb tests.

Of course, while no demonic forces or supernatural agents played a part in these incidents, radiation is an invisible spectre that when not treated with respect can mean the end for those who carelessly handle it.


The Demon Core is popular culture and finding our more

There are a number of great articles about the Demon Core. The best place to start is Wikipedia

There was also a great piece in The New Yorker by Alex Wellerstein which includes pictures showing a reconstruction of the room where the second incident occurred, you can read it here;

In the film Fat Man and Little Boy (released 1989) the Slotin and Daghlian incidents were combined and fictionalized. You can see the clip on YouTube here:

The complete film can be bought here:

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