Physics: The Beta Particle

Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom, along with an unusual particle called an antineutrino. The neutrino is an almost massless particle that carries away some of the energy from the decay process. Because this electron is from the nucleus of the atom, it is called a beta particle to distinguish it from the electrons which orbit the atom.

Like alpha decay, beta decay occurs in isotopes which are “neutron rich” (i.e. have a lot more neutrons in their nucleus than they do protons). Atoms which undergo beta decay are located below the line of stable elements on the chart of the nuclides, and are typically produced in nuclear reactors. When a nucleus ejects a beta particle, one of the neutrons in the nucleus is transformed into a proton. Since the number of protons in the nucleus has changed, a new daughter atom is formed which has one less neutron but one more proton than the parent. For example, when rhenium-187 decays (which has a Z of 75) by beta decay, osmium-187 is created (which has a Z of 76). Beta particles have a single negative charge and weigh only a small fraction of a neutron or proton. As a result, beta particles interact less readily with material than alpha particles. Depending on the beta particles energy (which depends on the radioactive atom), beta particles will travel up to several meters in air, and are stopped by thin layers of metal or plastic.

High energy betas that travel through water sometimes produce Cerenkov Radiation, which in turn produces the blue glow seen around fuel and reactors.

Cerenkov Radiation

A charged particle emits Cerenkov radiation (light) in a cone around its direction of travel when it travels through any medium faster than the speed of light through that medium. (Cerenkov - is the name of the scientist who first recognized the nature of this effect and its possible use for distinguishing particle types.) Although the speed of light in a vacuum is the fastest speed that any particle or light can have, in a medium of any type light travels more slowly  because of its interactions with the electric fields of the atoms in the medium and so it is possible for a high energy particle to be faster than light in some material . The blue light in the pools of water you may have seen in pictures of nuclear power plants is Cerenkov radiation from particles produced in the reactor.