ABSTRACT
Systems with spin one–half are of especial interest, since this is the spin encountered in the stable particles: electrons, positrons, protons, and neutrons. (The neutron is stable only in an atomic nucleus.) In this case, the wave function is of the form ψ ¯ = [ a 1 / 2 ( r , t ) a − 1 / 2 ( r , t ) ] https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429136528/397e01c1-e101-4a47-b552-a910642bbb8c/content/eqn12_1.tif"/>
