In nuclear physics , beta decay is a type of radioactive decay where a beta particle (an electron or a positron ) is made and sent away, or emitted. When it is an electron, it is called beta minus , and changes a neutron into a proton . When it is a positron, it is beta plus and changes a proton into a neutron. The weak force makes Beta decay possible.

In regular matter ^† , as the neutron becomes a proton, but the number of nucleons stays the same, the atomic mass will change by 0, but the atomic number will increase by +1. In effect, we can say the β particle has an atomic number of "-1".

$${\displaystyle {\ce {^{16}_{6}C -> ^{16}_{7}N + ^{0}_{-1}\beta}}}$$

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