Demon Core - Second Incident

Second Incident

On May 21, 1946, physicist Louis Slotin and seven other Los Alamos personnel were in a Los Alamos laboratory conducting an experiment to verify the exact point at which a subcritical mass (core) of fissile material could be made critical by the positioning of neutron reflectors. The test was known as "tickling the dragon's tail" for its extreme risk. It required the operator to place two half-spheres of beryllium (a neutron reflector) around the core to be tested and manually lower the top reflector over the core via a thumb hole on the top. As the reflectors were manually moved closer and farther away from each other, scintillation counters measured the relative activity from the core. Allowing them to close completely could result in the instantaneous formation of a critical mass and a lethal power excursion. Under Slotin's unapproved protocol, the only thing preventing this was the blade of a standard flathead screwdriver, manipulated by the scientist's other hand. Slotin, who was given to bravado, became the local expert, performing the test almost a dozen separate times, often in his trademark bluejeans and cowboy boots, in front of a roomful of observers. Enrico Fermi reportedly told Slotin and others they would be "dead within a year" if they continued performing it.

While lowering the top reflector, Slotin's screwdriver slipped outward a fraction of an inch, allowing the top reflector to fall into place around the core. Instantly there was a flash of blue light and a wave of heat across Slotin's skin; the core had become supercritical, releasing a massive burst of neutron radiation. He quickly knocked the two halves apart, stopping the chain reaction and likely saving the lives of the other men in the laboratory, though it is now known that the heating of the core and shells stopped the criticality within milliseconds of its initiation. Slotin's body's positioning over the apparatus also shielded the others from much of the neutron radiation. He received a lethal dose of 1000 rads neutron/114 rads gamma in under a second and died nine days later from acute radiation poisoning. The nearest person to Slotin, Dr. Alvin C. Graves, was watching over Slotin's shoulder and was thus partially shielded by him, received a high but non-lethal radiation dose of 34 neutron/166 gamma rads. Graves was hospitalized for several weeks with severe radiation poisoning, developed chronic neurological and vision problems as a result of the exposure, and died of a heart attack 20 years later.

Besides Graves, the others in the room were Stanley Allan Kline of Chicago, IL, physicist, died in 2001; Marion Edward Cieslicki of Mt Lebanon, PA, 11 neutron/11 gamma rads, physicist, died of acute myelocytic leukemia in 1967, 21 years after the accident; Dwight Smith Young of Chicago, IL, photographer, 51 neutron/11 gamma rads, died of aplastic anemia and bacterial endocarditis in 1973, 27 years after the accident; Dr. Raemer E. Schreiber of Lafayette, IN, physicist, 9 neutron/3 gamma rads, died of natural causes at 88 in 1998, 52 years after the accident; Theodore Perlman of Louisiana, engineer, 7 neutron/2 gamma rads), "alive and in good health and spirits" as of 1978; Pvt. Patrick J. Cleary of New York City, security guard, 33 neutron/9 gamma rads, died in Korea in 1952 during the Korean War; Paul Long, machinist, and another unidentified machinist, these latter two in another part of the building.

After Slotin's accident, hands-on criticality experiments were stopped, and remote-control machines were designed by Dr. Schreiber, one of the survivors, to perform such experiments with all personnel at a quarter mile distance.