In nuclear physics, beta decay is a type of radioactive decay in which a beta particle (an electron or a positron) is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus (β−), while in the case of a positron emission as beta plus (β+).
Beta minus decay:
If the nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron. This electron is called a beta minus (β-) particle - this process is known as beta radiation.
A beta particle has a relative mass of zero, so its mass number is zero. As the beta particle is an electron, it can be written as 0-1e. However, sometimes it is also written as 0-1β.
The beta particle is an electron but it has come from the nucleus, not the outside of the atom.
Electrons are not normally expected to be found in the nucleus but neutrons can split into a positive proton (same mass but positive charge) and an electron (which has a negative charge to balance the positive charge) which is then ejected at high speed and carries away a lot of energy.
Beta decay causes the atomic number of the nucleus to increase by one and the mass number remains the same.
Positron (ß+) emission:
If the nucleus has too few neutrons, a proton will turn into a neutron and emit a fast-moving positron. This positron can be called a beta plus (β+) particle - this process is known as positron emission.
A positron is the antimatter version of an electron. It has the same relative mass of zero, so its mass number is zero, but a +1 relative charge. It can be written as 0+1e, however sometimes it is also written as 0+1β.
Beta plus decay - positron emission - causes the atomic number of the nucleus to decrease by one and the mass number remains the same.