Haroutyun Krikor Daghlian Jr., born May 4, 1921, was an American physicist with the Manhattan Project who accidentally irradiated himself on August 21, 1945, during a critical mass experiment at the remote Omega Site facility at Los Alamos National Laboratory in New Mexico, resulting in his death 25 days later, on September 15, 1945. Daghlian was memorialised on May 20, 2000, by the city of New London, with the erection of a memorial stone and flagpole in Calkins Park.
Daghlian was irradiated as a result of a criticality accident that occurred when he inadvertently dropped a tungsten carbide brick onto a 6.2 kg delta phase plutonium bomb core. This core, available at the close of World War II and later nicknamed the “Demon core”, also resulted in the death of Louis Slotin in a similar accident, and was used in the Able detonation, during the Crossroads series of nuclear weapon testing.
As a result of the incident, safety regulations for the project were scrutinized and revised. A special committee was established to review any similar experiments and recommend appropriate safety procedures. These procedures included needing a minimum of two people involved in such an experiment; at least two instruments monitoring neutron intensities, each with audible alerts; and a prepared plan for operating methods and any contingencies which may occur during an experiment. Additionally, discussions and designs for remote-controlled test devices were initiated, which eventually led to the creation of the Godiva device. These changes did not prevent another criticality accident at Los Alamos: Louis Slotin was killed in 1946 while performing criticality tests on the same core that killed Daghlian.