On 21 August 1945, laboratory assistant Harry Daghlian, one of Slotin's close colleagues, was performing a criticality experiment when he accidentally dropped a heavy tungsten carbide brick onto a 6.2-kilogram (14 lb) plutonium–gallium alloy bomb core, later nicknamed demon core, which would later also kill Slotin. The 24-year-old Daghlian was irradiated with a large dose of neutron radiation. Later estimates suggested that this dose might not have been fatal on its own, but he then received additional delayed gamma radiation and beta burns while disassembling his experiment. He quickly collapsed with acute radiation poisoning and died 25 days later in the Los Alamos base hospital.