One reaction that some large nuclei can undergo is fission, where the nucleus splits into two or more pieces if struck by a neutron with enough energy. This process generates two more atoms plus often more neutrons: if the neutrons have the right energy they can then cause other nuclei to fission and so on. This is a chain reaction and is the source of power behind A-bombs and nuclear power plants, although the fissioning rate in the former is a wee bit faster than in the latter.

Quite often there are multiple possible fission products: for example, the isotope ²³⁵₉₂U used in nuclear power plants has several possible fission products

• ²³⁵₉₂U + ¹₀n -> ⁹⁰₃₇Rb + ¹⁴⁴₅₅Cs + 2¹₀n
• ²³⁵₉₂U + ¹₀n -> ⁸⁷₃₅Br + ¹⁴⁶₅₇La + 3¹₀n
• ²³⁵₉₂U + ¹₀n -> ⁷²₃₀Zn + ¹⁶⁰₆₂Sm + 4¹₀n

The energy released by a fission reaction can be computed by comparing the masses of the products and the reactants and using the mass-energy relationship DE = Dmc² to convert this to energy.

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