In nuclear physics, beta decay represents the emission of a beta particle (an electron or a positron) from the nucleus. In the case of electron emission, it is referred to as beta minus (β−), while in the case of a positron emission as beta plus (β+). The emitted beta particles have a continuous kinetic energy spectrum, with energies starting from 0 to a maximum energy (Q) limited by the parent and daughter nuclear states. The most energetic beta particles are ultrarelativistic, with speeds close to the speed of light.
- β− decay
In β− decay, the weak interaction converts a neutron (n) into a proton (p) while emitting an electron (e−) and an electron antineutrino (νe):
n → p + e− + νe
This type of beta decay usually occurs in neutron rich nuclei.
- β+ decay
In β+ decay, energy is used to convert a proton into a neutron, a positron (e+) and a neutrino (νe):
energy + p → n + e+ + νe
So, unlike β−, β+ decay cannot occur in isolation, because it requires energy, the mass of the neutron being greater than the mass of the proton. β+ decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.
- Electron capture (K-capture)
Another type of decay is the K-capture. It consists of an electron being captured from the electron cloud by the nucleus and the emission of a neutrino (anytime the β+ decay can occur energetically, it is accompanied by a K-capture). The decay can be described as:
energy + p + e− → n + ν
This decay is called the K-capture because the closest electron is located in the K shell (the electron cloud is divided into shells, each one more further than the previous one from the nucleus; they are named K, L, M, N, P and so on) and it has the grater probability of being captured by the nucleus.
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