The interesting thing to me was the the two supercritical experiments that led to imminent death were both with the same core, dubbed by the research team the &quot;demon core.&quot;<p>Daghlian was experimenting with the plutonium core to determine exactly how close the core was to supercriticality by stacking bricks of tungsten carbide (a neutron reflector about twice the density of steel.) He slipped and one of the bricks fell directly onto the core. Daghlian said later he knew at that moment he was dead. He threw the brick off the core, but it was too late. The resulting neutron burst killed him a few weeks later.<p>Interestingly, this same core also caused the death of a second professor, Loius Slotin. Slotin was attempting to perform the same task, determining the point of supercriticality, but using a different approach.<p>In this case a beryllium sphere(!), another neutron reflector, cut into two hemispheres were slowly lowered together, and the resulting neutron levels were measured.<p>Slotin was famously reckless, and in his insanity, he developed the apparatus such that the only thing keeping the two hemispheres from completely joining and producing an immediate reaction was a flat head screwdriver he slowly twisted. Enrico Fermi said several times &quot;He&#x27;s already dead. It&#x27;s only a matter of whether others die with him.&quot;<p>Sure enough, one day Slotin slipped, the core went briefly supercritical, and the massive dose of radiation killed him.<p>A superstition developed around the core, and although it was originally slated for wartime testing, the team left it on the shelf until after the war, when it was eventually detonated in a test at Bikini Atoll.