Which Technicians Handled The Demon Core During Fatal Tests?

I still get a chill thinking about those cramped lab rooms at Los Alamos, the hum of equipment and the quiet confidence everyone had back then. The two technicians who actually handled the infamous 'demon core' during the fatal incidents were Harry Daghlian and Louis Slotin. Harry Daghlian, a young physicist in his twenties, was working alone in late August 1945 stacking tungsten-carbide bricks as a neutron reflector around the core when one brick slipped and fell onto the assembly. That single mistake produced a prompt increase in reactivity — he received a lethal dose of radiation and died a few weeks later. The accident was heartbreaking because it came down to one moment of bad luck and the brutal physics of a supercritical assembly.

The second incident, less than a year later in May 1946, involved Louis Slotin. He was famous for performing delicate criticality experiments — the so-called 'tickling the dragon's tail' technique — where a beryllium shell was used as a reflector around the plutonium core and separated by a small gap. Slotin used a screwdriver to keep the halves apart during a demonstration; when the screwdriver slipped the shells closed, the core went prompt critical. Slotin took the brunt of the radiation and passed away about a week and a half later. Several colleagues and supervisors were present in the room during that test, and the event led to a major tightening of safety procedures and a rethinking of how these experiments should be performed. Reading about these incidents always reminds me how dangerous hands-on work with fissile material was before remote tooling and strict protocols became standard—human curiosity and skill were mixed with dreadful risk, and the losses left a deep mark on the laboratory community.

If you want the short, direct version I usually tell friends at meetups: the two technicians who actually handled the plutonium assembly in the fatal tests were Harry Daghlian (he dropped a tungsten-carbide brick onto the core in August 1945) and Louis Slotin (he was performing the mirror/reflector test in May 1946 and the screwdriver slipped). Both incidents produced a prompt critical excursion; Daghlian died a few weeks after his exposure, and Slotin died about nine days after his accident. There were other scientists and technicians around — supervisors and observers who later documented the events — but Daghlian and Slotin were the ones physically manipulating the core during the catastrophic moments. These tragedies are often referenced when people talk about how the Los Alamos labs shifted to remote handling and stricter safety rules, and they stick with me as stark lessons about how tiny mistakes can have enormous consequences.