Читать книгу Encyclopedia of Renewable Energy - James Speight G., James G. Speight - Страница 138

Beta decay (β-decay) is a type of radioactive in which a beta particle (a fast energetic electron or positron) is emitted from an atomic nucleus which transforms the original nuclide to an isobar of that nuclide.

By definition, an isobar is an atom (nuclide) of different chemical elements that have the same number of nucleons. Correspondingly, an isobar differs in atomic number (or the number of protons) but has the same mass number. An example of a series of isobars is ⁴⁰S, ⁴⁰Cl, ⁴⁰Ar, ⁴⁰K, and ⁴⁰Ca.

Thus, the beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino or, conversely, a proton is converted into a neutron by the emission of a positron with a neutrino in the positron emission reaction. Neither the beta particle nor its associated (anti-)neutrino exist within the nucleus prior to beta decay, but are created in the decay process. By this process, unstable atoms obtain a more stable ratio of protons to neutrons. The probability of a nuclide decaying due to beta and other forms of decay is determined by the nuclear binding energy.

Thus, the two types of beta decay are known as beta minus and beta plus. In the former [beta minus decay (β⁻ decay)], a neutron is converted to a proton, and the process creates an electron and an electron antineutrino, while in beta plus decay (β⁺ decay, also known as positron emission), a proton is converted to a neutron and the process creates a positron and an electron neutrino.

An example of electron emission (β⁻ decay) is the decay of carbon-14 (1⁴C) into nitrogen-14 (¹⁴N) with a half-life on the order of 5,730 years:

In this form of decay, the original element becomes a new chemical element (nuclear transmutation) and the new element has an unchanged mass number (A) but anatomic number (Z) that is increased by one. As in all nuclear decays, the decaying element (in this case ¹⁴₆C) is the parent nuclide, while the resulting element (in this case ¹⁴₇N) is known as the daughter nuclide.

Another example is the decay of hydrogen-3 (³H, tritium) into helium-3 (³He) with a half-life on the order of 12.3 years:

An example of positron emission (β⁺ decay) is the decay of magnesium-23 (²³Mg) into sodium-23 (²³Na) with a half-life on the order of 11.3 seconds:

Beta+ decay (β⁺ decay) also results in nuclear transmutation, with the resulting element having an atomic number that is decreased by one.

See also: Alpha Decay, Alpha Particle, Nuclear Energy.