Isotopic Spin and Antinucleon-Nucleon Scattering

The total isotopic spin operator and its square are determined for the quantized nucleon-antinucleon field. In the customary configuration space representation, it is found that in the formula for the total isotopic spin of a system of nucleons and antinucleons, the antinucleons contribute terms with the transposed negatives of the $\tau$ operators replacing the corresponding $\tau \text{'}\mathrm{s}$. The form that has been usually anticipated is found only after a suitable canonical transformation. The results are specifically applied to a two-particle system consisting of a nucleon and an antinucleon.