From Big Medical Encyclopedia

BETA DECAY — the radioactive transformation of an atomic nucleus which is followed by emission of beta particles. At B. - the river happens intranuclear transformation of a neutron into a proton to emission from a kernel of an electron and a neutrino (electronic, a beta - - disintegration) or transformation of a proton into a neutron with emission of a positron and neutrino (positron a beta + - disintegration).

B. - river — the main type of radioactive transformation for isotopes with sequence numbers less than 60. The kernels having surplus of neutrons in relation to number of neutrons in a steady kernel with the same mass number the most part test electronic B. - river. The kernels having surplus of protons usually test positron B. - the river or electron capture consisting in capture by a kernel of an electron from an electron shell of atom. At electron capture, as well as at positron B. - river, one of protons of a kernel turns into a neutron therefore electron capture competes with a beta + - by disintegration it is also observed most often at heavy elements.

For the majority of beta and radioactive kernels half-life (see) makes size from fractions of a second up to several years, however there are kernels with very big half-lives. E.g., half-life for radioactive potassium-40 reaches more than one billion years, for chlorine-36 — several hundred thousands of years and for carbon-14 — more than five thousand years.

See also Beta radiation .