Spectral distributions for coherent and incoherent bremsstrahlung produced by electrons on thin diamond radiators are calculated accurately by a Monte Carlo procedure. Realistic descriptions of the electron beam and the physical processes within the radiator have been implemented. Results are compared to measured data. A faster calculation at only a slight loss of precision is possible using analytical expressions which can be derived after simplifying assumptions.

The ${}^{12}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},pp)$ and ${}^{12}\mathrm{C}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},pn)$ reactions have been studied for ${E}_{\ensuremath{\gamma}}=160\ensuremath{-}350$ MeV using linearly polarized photons from the Glasgow tagged photon spectrometer at the Mainz microtron MAMI. Both reaction channels show a negative photon asymmetry $\ensuremath{\Sigma}$ for missing energies ${E}_{m}$ below 70 MeV, where direct emission nucleon pairs is expected. A strong peak at low ${E}_{m}$ is observed in ${\ensuremath{\Sigma}}_{(\ensuremath{\gamma},pp)},$ but not in ${\ensuremath{\Sigma}}_{(\ensuremath{\gamma},pn)}.$ Further differences between the two reaction channels are observed in the ${E}_{\ensuremath{\gamma}}$ dependence of $\ensuremath{\Sigma}$ and in the angular distributions of differential cross sections for photons polarized parallel, or perpendicular, to the reaction plane. Theoretical calculations using an unfactorized distorted wave treatment of direct two-nucleon emission do not agree with the magnitude of the photon asymmetry or the angular dependence of the differential cross sections for either channel. For ${E}_{m}>70$ MeV and ${E}_{\ensuremath{\gamma}}>250$ MeV, $\ensuremath{\Sigma}$ has a substantial negative value which is similar for both reaction channels. This is attributed to two-step reactions following initial quasifree pion production.

The photon asymmetry measurement of 2N knock-out reactions on 4He provide new insights in the nature of correlations caused by the short distance repulsion of the NN interaction. Additionally the results show first indications of tensor correlations. A very precise description of the production of coherent bremsstrahlung will be presented which reduces systematic errors from the degree of polarisation.

The photon asymmetry (Σ) of the 12C(γ→,pn) reaction has been measured using linearly polarised tagged photons at the Mainz microtron MAMI for Eγ=180–340 MeV. The data have been analysed in separate missing energy (Em) regions corresponding to the ejection of nucleons from (1p)2 and (1p)(1s) shells. The measured Σ values for both Em regions are smaller in magnitude than corresponding 2H data, but the (1p)2 results have a similar Eγ dependence. Calculations of direct two-nucleon emission overestimate the magnitude of Σ at all photon energies.

The photon asymmetry (Sigma) of the C-12((gamma)over-right-arrow,pn) reaction has been measured using linearly polarised tagged photons at the Mainz microtron MAMI for E-gamma = 180-340 MeV. The data have been analysed in separate missing energy (E-m) regions corresponding to the ejection of nucleons from (lp)(2) and (lp)(ls) shells. The measured Sigma values for both E-m regions are smaller in magnitude than corresponding H-2 data, but the (lp)(2) results have a similar E-gamma dependence. Calculations of direct two-nucleon emission overestimate the magnitude of Sigma at all photon energies. (C) 1999 Elsevier Science B.V. All rights reserved.