Fission of an atomic nucleus into two parts of the same size caused by the collision of a particle. Nuclear fission may also occur spontaneously in the case of very heavy nuclei; (See ‘fission, spontaneous’). The capture of a neutron induces fission of the nucleus of uranium-235. During the fission, in general two – more rarely three – fission products, two to three neutrons and energy are generated.

Example for nuclear fission of U-235

In the uranium nucleus the nucleons are bound with an average energy of about 7.6 MeV per nucleon. In the fission product nuclei, the medium binding energy per nucleon amounts to approx. 8.5 MeV. This difference in binding energy of 0.9 MeV per nucleon is released in the nuclear fission. Since the uranium nucleus has 235 nucleons, a quantity of energy of about 210 MeV is released per fission. It is made up of the following partial amounts:

  • kinetic energy of fission products 175 MeV,
  • kinetic energy of fission neutrons 5 MeV,
  • energy of the gamma radiation occurring during the fission 7 MeV,
  • energy of beta and gamma radiation during the decay of the radioactive fission products 13 MeV,
  • energy of the neutrinos 10 MeV.

Course of nuclear binding energy

Due to the neutrons released during the nuclear fission a chain reaction is possible in principle. Facilities where fission chain reactions are initiated in a controlled manner are called nuclear reactors.