Does positron decay result in nuclear transmutation?

1 Answer
May 21, 2014

Yes, Positron decay results in nuclear transmutation.

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

The atomic number Z decreases by 1 while the mass number A remains the same.

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

The neutrino is often emitted in nuclear equations because it has no mass and no charge. Its only function is to carry off some of the excess energy.

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. This makes the nucleus more stable.

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.

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

Sodium-23 has 12 neutrons and 11 protons. The neutron:proton ratio is 12:11 = 1.09:1, so sodium-23 has a stable nucleus.

Other examples of positron emission are:

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

#""_5^8"B" → ""_4^8"Be" + ""_1^0e + ν_e#

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