Which radiation consists of high-speed electrons?

Radiation consisting of high-speed electrons is beta radiation. In beta-minus decay, an unstable atomic nucleus emits a high-energy electron, called a beta particle, along with an antineutrino.

Beta radiation is produced when a neutron in the nucleus changes into a proton. The atomic number increases by one while the mass number stays the same, so the atom becomes a different chemical element. In beta-plus decay, the emitted particle is a positron rather than an electron, but both processes are classified as beta decay.

Beta particles are ionizing because they can knock electrons out of atoms as they pass through matter. They penetrate farther than alpha particles but generally less far than gamma rays. A beta source can travel roughly a meter through air, depending on the particle’s energy, and is commonly shielded with materials such as plastic or thin aluminum.

Neutron radiation consists of neutrons, gamma radiation consists of high-energy electromagnetic photons, and alpha radiation consists of helium nuclei. Those distinctions describe the particles involved, not simply how dangerous or penetrating the radiation may be.