August 26, 1945. Los Alamos National Laboratory, New Mexico.

Twenty four year old Harry Daghlian is working late, and alone. Both are violations of safety protocol, but Harry doesn’t care. He’s good at his job, and he’s careful. He doesn’t have to be working this late, six days ago the Japanese surrendered, and the war is over. But, that doesn’t mean his work isn’t still important. The bombs he helped build won the war, and he’s going to keep making them as long as he can.

This night, Harry is working on placing the final tungsten bricks in a neutron reflector around plutonium bomb core. The reflector would lessen the amount of plutonium needed for the bomb to go critical. When he was placing the final brick, his hand slipped. The small brick hit the core, and sent it critical. A blue light issued out from the core, dosing him with radiation. Frantic, Harry knocks off the brick in hopes that it will stop the reaction. Unfortunately, it doesn’t and he’s forced to disassemble much of the neutron reflector before the core retreats from criticality.

He saved the lives of everyone at the lab, but there was nothing to be done for Harry Daghlian. He died twenty one days later from accute radiation poisoning.

For many of those twenty one days, one of the old guard of Los Alamos, Louis Slotin, could be found by Harry’s side. Louis was known informally as the chief armorer of the United States. He had built the test bomb that was detonated at Trinity. He wanted to get out of military work, but there wasn’t anyone else with his experience or skill for building bombs.

Nine months after the accident that took the life of his friend Harry, Louis was working with the same core. Instead of using several tungsten bricks for the neutron reflector, the new construction relied on two beryllium hemispheres to encapsulate the plutonium core. The core was already placed in the bottom hemisphere as Louis moved the top into position. He was aligning the top with the use of his hand and a screwdriver, when he slipped. The top hemisphere struck the core, causing it to go critical. A burst of blue light and a wave of heat struck the scientists in the room. Instinctively, Louis pulled his hand up, his thumb still hooked into the beryllium hemisphere. The criticality was stopped, and the lives of the men in the room were saved. But, like his friend, Louis wasn’t so lucky.

Louis Slotin died nine days later of acute radiation poisoning. Another victim of what came to be known as the demon core.

The assembly Louis was working on was to be the final test of the demon core. It was fitted into a bomb and used as the ABLE test during Operation Crossroads at the Bikini Atoll.