The relativistic nuclear shell model with large scalar and time-component vector potentials predicts very strongly bound negative-sea states. Such states may be absent in alternative versions of the model which contains a tensor term. The process (γ,pp¯) in the presence of a nucleus could form a highly excited p¯-nucleus with gamma ray energy less than 2M. The predicted cross section for γ${+}^{16}$O${\to }_{{}_{p¯}{}^{15}{}_{}{}^{}\mathrm{N}+\mathit{p}}$ has a threshold 1.2 GeV and rises to about 5 μb by 1.6 GeV.

• Received 14 March 1988

DOI:https://doi.org/10.1103/PhysRevC.38.813