Harry K . Daghlian , Jr . Haroutune Krikor Daghlian , Jr . ( May 4 , 1921 – September 15 , 1945 ) was an Armenian - 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 . Daghlian was irradiated as a result of a criticality accident that occurred when he accidentally 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 . Early life . Daghlian was the first of three children born to Margaret Rose Currie and Haroutune Krikor Daghlian . Soon after his birth in Waterbury , Connecticut , the family moved across state to the coastal town of New London . He was educated at Harbor Elementary School , where he played violin in the school orchestra , and at Bulkeley High School . In 1938 , at the age of 17 , he entered the Massachusetts Institute of Technology , intending to study mathematics , but became interested in physics , particularly particle physics , which was then emerging as an exciting new field . This led him to transfer to the West Lafayette , Indiana campus of Purdue University , from which he obtained a Bachelor of Science degree in 1942 . He then commenced work on his doctorate . In 1944 , he joined Otto Frisch ' s Critical Assembly Group at Los Alamos . Criticality accident . In the experiment on August 21 , 1945 , Daghlian was attempting to build a neutron reflector by manually stacking a set of 4 . 4 kg tungsten carbide bricks in an incremental fashion around a plutonium core . The purpose of the neutron reflector was to reduce the mass required for the plutonium core to attain criticality . As he was moving the final brick over the assembly , neutron counters alerted Daghlian to the fact that the addition of this brick would render the system supercritical . As he withdrew his hand , he accidentally dropped the brick onto the center of the assembly . Since the assembly was nearly in the critical state , the accidental addition of the last brick caused the reaction to go immediately into the prompt critical region of supercritical behavior . This resulted in a power excursion . Daghlian reacted immediately after dropping the brick and attempted to knock off the brick without success ; he was forced to partially disassemble the tungsten - carbide pile to halt the reaction . Daghlian was estimated to have received a dose of 510 rem ( 5 . 1 Sv ) of neutron radiation , from a yield of 10 fissions . Despite intensive medical care , he soon developed symptoms of severe radiation poisoning and died 25 days later after falling into a coma . He was the first known fatality caused by a criticality accident . Legacy . 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 . Daghlian was memorialized on May 20 , 2000 , by the city of New London , with the erection of a memorial stone and flagpole in Calkins Park .