The12C(γ,2N) reactions have been studied using tagged photons ofE γ = 114–600 MeV at the Mainz microtron (MAMI). The cross sections of the12C(γ,pn) reaction and the shape of12C(γ,pp) spectra compare well to model predictions over a wide range of photon energies and missing energies, suggesting that the dominant mechanisms of photonuclear reactions are understood.

The 12C(γ,pn) and 12C(γ,pp) reactions have been studied using tagged photons of energy Eγ = 150–400 MeV. Recoil momentum distributions are compared to the results of Monte Carlo calculations based on a two-nucleon photon absorption model and two different phase space models. The 12C(γ,pn) data at low missing energy are consistent with absorption on 1p2 and 1s1p nucleon pairs.

The C-12(gamma,pn) and C-12(gamma,pp) reactions have been studied using tagged photons of energy E(gamma) = 150-400 MeV. Recoil momentum distributions are compared to the results of Monte Carlo calculations based on a two-nucleon photon absorption model and two different phase space models. The C-12(gamma,pn) data at low missing energy are consistent with absorption on 1p(2) and 1s1p nucleon pairs.

The (gamma,NN) reactions at intermediate energies have long been suggested as a source of information on nucleon-nucleon correlations in nuclei. In particular, the (gamma,pp) reaction may hold particular promise because it is much less sensitive to medium range MEC effects. In the past limited intensity and resolution of the available photon beams has hindered progress. Using the Galsgow photon tagging spectrometers at the Mainz MAMI-A and MAMI-B electron microtrons, data on both (gamma,pn) and (gamma,pp) reactions in 12C have now been obtained with much improved energy resolution (~7 MeV in missing energy). The very recent MAMI-B data extends up to 750 MeV which permits shorter range effects to be sought.

Because of its nuclear structure 6Li is particularly well suited for the study of the (gamma,np) reaction mechanisms. The large overlap of 6Li with an alpha-d cluster has been employed as a tool also in other reactions like pion absorption: (e,e'd) and two-nucleon transfer reactions. The knock-out of the two nucleons from the p-shell, i.e. the removal of the d-cluster leaving the 4He core intact is well separated in energy by ~20 MeV from the case where the alpha core is broken up. In particular for the ground state transition there exist good 3-body cluster wave functions to be used as theoretical input in studies of the reaction mechanjsms. So far we have investigated the 6Li(gamma,np) reaction at photon energies of ~73 MeV at MAXLAB in Lund, and around ~140 MeV at MAMI A, Mainz. Within limited statistical errors the quasideuteron model gave a good description of this process.