Complex sentence: On August 21,1945, the plutonium core produced a burst of neutron radiation that irradiated Harry Daghlian, a physicist who made a mistake while working alone doing neutron reflection experiments on the core.
Split into simpler sentences: On August 21,1945 the plutonium core produced a burst of neutron radiation that caught Harry Daghlian in its path. Daghlian was a physicist who made a mistake while working alone performing neutron reflection experiments on the core.