Positron emission

Although positron emission doesn’t occur with naturally occurring radioactive isotopes, it does occur naturally in a few human-made ones. A positron is essentially an electron that has a positive charge instead of a negative charge.  A positron is formed when a proton in the nucleus decays into a neutron and a positively charged electron. The positron is then emitted from the nucleus. This process occurs in a few isotopes, such as potassium-40 (K-40), as the following equation shows:

The K-40 emits the positron, leaving an element with a mass number of 40 (40 – 0) and an atomic number of 18 (19 – 1). An isotope of argon (Ar), Ar-40, has been formed.