# Why does Se-82 undergo double beta decay?

Looking at the decay chain, I saw it undergoes double beta decay. How is it feasible for something to undergo a simultaneous double decay?

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The condition for double beta decay to be the preferred mode are that the energy (mass) of the three states

• The initial nucleus (m)
• The would-be single-beta-decay daughter plus the electron and the anti-neutrino (s)
• The double-beta-decay daughter plus the two electrons and the two anti-neutrinos (d)

have a relationship like

$$E_d < E_m < E_s \,.$$

The result is that it is not possible for a single decay to proceed (there is not enough energy) but it is possible for a double decay to happen (though it will be a slow process).

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