n.
or isobaric spin or isotopic spin
Property characteristic of families of related subatomic particles differing mainly in the values of their electric charge .
The families are known as isospin multiplets. The components of atomic nuclei, the neutron and the proton , form an isospin doublet since they differ only in electric charge and subsidiary properties. They are considered different versions of the same object, called a nucleon. The isospin of a nucleon has a value of 1 2 .