Nucleon-Antinucleon Interaction at Intermediate Energies

The Yukawa interaction between nucleon and antinucleon is investigated in the intermediate energy range (50 to 200 Mev) where it is shown that the details of the short-range forces are unimportant; that is, cross sections are primarily determined by the pion exchange potential for distances greater than 10^-13 cm. Numerical calculations by the WKB method, using two possible forms of the potential, give nucleon-antinucleon cross sections several times larger than the nucleon-nucleon cross sections at corresponding energies. This large difference is due to systematic cancellation effects in the nucleon-nucleon interaction which are removed in the nucleon-antinucleon system. It is shown that irregularities in the annihilation cross section as a function of energy are to be expected as a result of the sudden onset of individual partial waves.