A beta particle is often an electron, but can also be a positron, a positively-charged particle that is the anti-matter equivalent of the electron. In terms of safety, beta particles are much more penetrating than alpha particles, but much less than gamma particles.

An important process in beta decay involves a neutron turning into a proton by giving up an electron:

The extra particle on the end is an antineutrino, with the e subscript denoting that it is an electron antineutrino. The existence of the neutrino was proposed by Pauli in 1930 to explain what seemed like violations of the laws of conservation of energy and conservation of momentum in the beta decay process.

If an electron is involved, the number of neutrons in the nucleus decreases by one and the number of protons increases by one. An example of such a process is:

Use the data from Appendix F to analyze this reaction:

The atomic mass of Th-234 is 234.043596 u
The atomic mass of Pa-234 is 234.043302 u

We don't have to add the mass of the electron because the mass for Pa-234 includes 91 electrons, and we had 90 to start with. It's already built into the mass for Pa-234, in other words.

The mass difference is 0.000294 u, equivalent to 0.274 MeV of energy. This is primarily carried away by the electron and the antineutrino after the reaction. Recent experiments indicate that neutrinos (and antineutrinos) have some mass, but it is negligible compared to the masses we're using here.

If a nucleus decays by releasing a positron, the reaction looks like this:

In that case a proton turns into a neutron, and there is an electron neutrino on the right side of the equation. A positron has a charge of +e and has the same mass as an electron.