What is a beta particle?

• A. A helium nucleus emitted in alpha decay.
• B. A photon emitted in gamma decay.
• C. A high-speed electron emitted in the decay of a radioactive isotope.
• D. A neutron ejected during fission.

Answer: (C)

A beta particle is the fast electron released during beta decay. In beta minus decay, a neutron transforms into a proton and emits an electron plus an antineutrino; the emitted electron is the beta particle. In beta plus decay, a proton becomes a neutron and emits a positron plus a neutrino, which is also categorized as a beta particle in many contexts. This distinguishes it from other radiation types: an alpha particle is a helium nucleus from alpha decay, a gamma ray is electromagnetic radiation (a photon), and a neutron can be released in fission but is not a beta particle. Thus, a high-speed electron emitted in the decay of a radioactive isotope captures the essence of a beta particle.