Beta particles
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay.
. There are two forms of beta decay, beta-minus and beta-plus, which respectively give rise to the electron and the positron.Beta-minus decay.
An unstable atomic nucleus with an excess of neutrons may undergo beta-minus decay, where a neutron is converted into a proton, an electron and an electron-type antineutrino (the antiparticle of the neutrino)
This process is mediated by the weak interaction. The neutron turns into a proton through the emission of a virtual W- boson. At the quark level, W- emission turns a down-type quark into an up-type quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark). The virtual W- boson then decays into an electron and an antineutrino.
Beta decay commonly occurs among the neutron-rich fission byproducts produced in nuclear reactors. Free neutrons also decay via this process.
This is the source of the copious amount of electron antineutrinos produced by fission reactors.