Isotopic Spin Selection Rule for Electric Dipole Transitions

The validity of the isotopic spin quantum number in nuclei provides a selection rule on electric dipole transitions. The extent to which this selection rule is violated provides a means of experimentally determining the isotopic spin impurity of nuclear states providing that the radiation widths for uninhibited $E1\mathrm{}$ radiation can be predicted. The sources of possible variations of $E1\mathrm{}$ matrix elements are discussed with reference to the reliability of predicted $E1\mathrm{}$ radiation widths in nuclei for $A\le 20$ and excitation energy ∼15 Mev. Higher order corrections to the $E1\mathrm{}$ selection rules are determined and found to be negligible compared to the effects of isotopic spin impurity. It is concluded that the isotopic spin selection rule on $E1\mathrm{}$ transitions provides a sensitive test of charge independence. Isotopic spin impurity determined in this way can be attributed solely to the Coulomb potential.