On May 21, 1946, Slotin and seven other colleagues performed an experiment that involved the creation of one of the first steps of a fission reaction by placing two half-spheres of beryllium (a neutron reflector) around a plutonium core. The experiment used the same 6.2-kilogram (13.7 lb) plutonium core that had irradiated Daghlian, later called the “Demon core” for its role in the two accidents. Slotin grasped the upper beryllium hemisphere with his left hand through a thumb hole at the top while he maintained the separation of the half-spheres using the blade of a screwdriver with his right hand, having removed the shims normally used. Using a screwdriver was not a normal part of the experimental protocol. Graves was standing right behind Slotin.
At 3:20 p.m., the screwdriver slipped and the upper beryllium hemisphere fell, causing a “prompt critical” reaction and a burst of hard radiation. At the time, the scientists in the room observed the “blue glow” of air ionization and felt a “heat wave”. In addition, Slotin experienced a sour taste in his mouth and an intense burning sensation in his left hand. Slotin instinctively jerked his left hand upward, lifting the upper beryllium hemisphere and dropping it to the floor, ending the reaction. However, he had already been exposed to a lethal dose (around 2100 rems, or 21 Sv) of neutron and gamma radiation. Slotin's radiation dose was equivalent to the amount that he would have been exposed to by being 1500 m (4800 ft) away from the detonation of an atomic bomb.
This is why I’m somewhat worried about anything radioactive.