Critical historical revision of LA-1; the first criticality accident in history

This work of historic character and interest, examines the mechanical, physical, dosimetric and clinical aspects of the first criticality accident in history, the so called LA-1 (for Los Alamos-1) event, reference is made to the volume of literature this event has generated in the past 30 years and attempts are made to interpret this literature. On August 21 1945, the first uncontrolled criticality excursion in history occurred at the Los Alamos Scientific Laboratory, in New Mexico. In 1952 Hempelmann published what until the mid 1960´s was considered the definitive account of the accident. Subsequently, a number of then secret but recently declassified studies have seriously questioned Hempelmann´s account. The accident occurred during the course of experiments with a subcritical 6.19 kg. sphere of Pu-239. The operator, aware of the risks, decided nevertheless to control the experiment manually since a reliable remote control mechanism was not available. The sphere was surrounded with enough tungsten carbide bricks of high neutron reflectivity to just bring the structure to criticality. For reasons that remain unclear to this day, the neutron flux increased abruptly and attempting to remove one of the bricks, the operator accidentally dropped it on top of the Pu sphere. The assembly instantly achieved prompt-criticality releasing such power that a bright blue light (Cerenkov radiation) illuminated the newspaper that a security guard was reading at distance of 4 m. The operator manually removed the fallen brick and the structure reverted to a subcritical state. Based on careful physical reconstructions and numerical simulations of the accident, the neutron-gamma exposure rate around the structure was estimated to be of the order of 10⁸ R/sec. The operator was admitted to Los Alamos Hospital and within hours developed severe leukopenia (3000 mm^-1) and was placed in a reverse isolation chamber with positive pressure. He was treated with high doses of antibiotics and blood coagulating agents, in addition to the administration of multiple blood transfusions. He expired on the 29^th day after the accident from generalized infection. The security guard survived for 33 years and his clinical evolution until death from acute myelogenous leukemia is presented