In other cases , and depending on the kinetic energy of the neutron , the capture of a neutron can cause nuclear fission — the splitting of the atomic nucleus into two smaller nuclei . If the fission requires an input of energy , that comes from the kinetic energy of the neutron . An example of this kind of fission in a light element can occur when the stable isotope of lithium , lithium-7 , is bombarded with fast neutrons and undergoes the following nuclear reaction : In other words , the capture of a neutron by lithium-7 causes it to split into an energetic helium nucleus ( alpha particle ) , a hydrogen-3 ( tritium ) nucleus and a free neutron . The Castle Bravo accident , in which the thermonuclear bomb test at Enewetak Atoll in 1954 exploded with 2.5 times the expected yield , was caused by the unexpectedly high probability of this reaction
Castle Bravo
Castle Bravo
Neutron activation