The total photoabsorption cross section of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and the longitudinal response function in the range of momentum transfers from 200 to 500 MeV/c are evaluated in the random-phase approximation. The random-phase-approximation polarization propagator is calculated by generalizing the doorway-state method previously developed for the Tamm-Dancoff approximation. The random-phase-approximation result is compared to the Tamm-Dancoff approximation and to experiment. The random-phase-approximation correlations cannot resolve the problem of missing strength in the quasielastic region in the range of momentum transfers between 300 and 500 MeV/c. At lower momentum transfer (200 MeV/c), as well as for photoabsorption, very good agreement with experiment can be obtained, provided other many-body effects are also taken into account. In our approach these other effects are accounted for by the imaginary part of the surface optical potential and by the width of the deeply bound hole states.

• Received 29 December 1986

DOI:https://doi.org/10.1103/PhysRevC.36.899