More than 50 years ago, in 1934, Chadwick and Goldhaber (ChG 34) published a paper entitled "A 'Nuclear Photo-effect': Disintegration of the Diplon by -y-Rays."l in the introduction: They noted "By analogy with the excitation and ionisation of atoms by light, one might expect that any complex nucleus should be excited or 'ionised', that is, disintegrated, by -y-rays of suitable energy", and furthermore: "Heavy hydrogen was chosen as the element first to be examined, because the diplon has a small mass defect and also because it is the simplest of all nuclear systems and its properties are as important in nuclear theory as the hydrogen is in atomic theory". Almost at the same time, in 1935, the first theoretical paper on the photodisinte gration of the deuteron entitled "Quantum theory of the diplon" by Bethe and Peierls (BeP 35) appeared. It is not without significance that these two papers mark the be ginning of photonuclear physics in general and emphasize in particular the special role the two-body system has played in nuclear physics since then and still plays. A steady flow of experimental and theoretical papers on deuteron photo disintegration and its inverse reaction, n-p capture, shows the continuing interest in this fundamental process (see fig. 1.1). 1 Introduction.- 2 Elementary theory and brief history.- 3 Formal theory for two-particle channels.- 3.1 Kinematics.- 3.2 The T-matrix.- 3.3 Density matrices.- 3.4 Cross section and polarization observables.- 3.5 Multipole decomposition and angular distributions.- 4 Methods of calculation for the T-matrix.- 4.1 Non-relativistic approach.- 4.2 Meson-exchange currents and isobar configurations.- 4.3 Relativistic effects.- 4.4 The diagrammatic approach.- 4.5 Covariant theory and dispersion relations.- 5 Unpolarized and polarized beam sources.- 5.1 Continuous bremsstrahlung and the monitoring problem.- 5.2 Monochromatic and quasi-monochromatic photon beams.- 5.3 Inverse reaction and detailed balance.- 5.4 Polarized beam sources.- 6 Experimental results for two-particle break-up.- 6.1 Total and differential cross sections.- 6.2 Information from analysis of all available experiments.- 6.3 Results from selected experiments.- 6.4 Experimental results for polarization observables.- 7 Comparison of theory and experiment.- 7.1 Total cross section and sum rules.- 7.2 Angular distributions.- 7.3 Differential cross section at 0° and 180°.- 7.4 Polarization observables.- 8 Conclusion and outlook.- References.
