During beta decay, the nucleus emits an electron (β⁻ decay) or a positron (β⁺ decay).

Here's a breakdown:

* β⁻ decay: A neutron in the nucleus transforms into a proton, emitting an electron and an antineutrino. This increases the atomic number of the element by 1.

* β⁺ decay: A proton in the nucleus transforms into a neutron, emitting a positron and a neutrino. This decreases the atomic number of the element by 1.

In both cases, the total number of nucleons (protons + neutrons) remains constant.