• When large atomic nuclei are hit with neutrons they can become highly unstable if the neutron is absorbed by the nucleus. The larger unstable nucleus breaks into two smaller 'daughter' nuclei and also release more neutrons, as well as beta and alpha particles and gamma.

• The two smaller atoms formed are themselves usually unstable and radioactive.

  • The nuclear fission equations below are a gross simplification of the process!

• This process is called nuclear fission and because it is accompanied by an enormous release of energy, it forms the basis of nuclear power. The radioisotope uranium-235  is particularly useful for energy generation by nuclear fission.

• Much of the energy released is initially the kinetic energy of the fission fragments, but collisions, radioactive decay etc. result in most of it changing to heat and some as electromagnetic radiation.

• The heat energy can be used to boil water to make steam to drive a turbine and electrical generator in a nuclear power station.

• The energy release is much greater than for exothermic chemical reactions eg 1g uranium nuclear fuel releases the same amount of energy as 1 tonne of coal (= 1000kg =  1000000g), a million x energy density factor!

• One consequence of fission is that more neutrons are formed, these in turn 'split' other atoms making even more neutrons.

• This is called a chain reaction and leads to acceleration in the atom 'splitting' and hence an even greater energy release.

• If uncontrolled a nuclear explosion results (a fission bomb based on uranium-235 was dropped on the Japanese city of Hiroshima in 1945, Nagasaki was hit by a plutonium based fission bomb).

• In nuclear reactors, rods of a 'moderator' like boron can lowered into the reactor core to absorb neutrons and slow down fission to keep the chain reaction under control. Note again, the balancing of nuclear equations for, in this case, fission reactions (somewhat simplified!) ...

, uranium split into lanthanum and bromine nuclei

, uranium split into molybdenum and lanthanum and a good balancing challenge!

• Unfortunately there is considerable amounts of highly radioactive waste from the nuclear power industry which must be disposed of safely. See health and safety, half-life and background radiation.

Website content copyright © Dr W P Brown 2000-2010 All rights reserved on revision notes, puzzles, quizzes, worksheets, x-words etc. * Copying of website material is not permitted * I do not personally endorse the adverts - but they do pay for the site!