E.3.7—Decay nuclear changes

Alpha decay

Alpha decay emits a ${}^{4}_{2}\mathrm{He}$ nucleus. The parent’s nucleon number decreases by 4 and proton number decreases by 2.

Beta decay

In beta-minus decay, a neutron becomes a proton and an electron is emitted, so $A$ is unchanged and $Z$ increases by 1. In beta-plus decay, a proton becomes a neutron and a positron is emitted, so $A$ is unchanged and $Z$ decreases by 1.

Gamma decay

Gamma emission changes the nucleus from an excited state to a lower energy state. Neither $A$ nor $Z$ changes.

Common trap

Do not change A during beta decay, and do not treat gamma emission as a change of element.