How does positron emission occur?

1 Answer
Mar 27, 2014

Positron emission occurs when a proton in a radioactive nucleus changes into a neutron and releases a positron and an electron neutrino.


A positron is a type of beta particle (β⁺). Another symbol for a positron is #" "_1^0e#. The symbol for an electron neutrino is #ν_e#.

Most nuclei are unstable if the neutron-proton ratio is less than 1:1, that is, if there are too many protons. They will decay to correct the imbalance.

Positron emission increases the number of neutrons and decreases the number of protons, making the nucleus more stable. In positron emission, the atomic number Z decreases by one while the mass number A remains the same.

Magnesium-23 has 12 protons and 11 neutrons. The neutron:proton ratio is 11:12 or 0.92:1. It undergoes positron emission to form sodium-23.

#" "_12^23Mg → _11^23Na + _1^0e + ν_e#

#" "_11^23Na# has 12 neutrons and 11 neutrons. The neutron:proton ratio is 12:11 = 1.09:1, so sodium-23 has a stable nucleus.

Other examples of positron emission are:

#" "_11^22Na → _10^22Ne + _1^0e + ν_e#

#" "_5^8B → _4^8Be + _1^0e + ν_e#

#" "_25^50Mg → _24^50Cr + _1^0e + ν_e#