Proton‐capture gamma rays as a spectroscopic tool

Proton‐capture gamma rays can be used to induce nuclear reactions at a well‐defined energy. The total intensity is considerably less (by a factor of at least a hundred) than the strong monoenergetic gamma rays from high‐flux nuclear reactors exploited for this purpose. On the other hand the energy of the gamma rays, depending on the target mass and the energies, can be varied over a range from 20 to 80 keV by changing the angle of observation with respect to the proton beam. This means that specific levels can be excited at will. Experiments done to data using these gamma rays are reviewed. These are resonance self‐absorption and fluorescence (capturing nucleus the same as resonating nucleus), resonance cross‐absorption and fluorescence (where use can be made of the polarization of capture gamma rays) of bound levels, and resonance absorption on unbound levels. A discussion of the relative merits of these techniques, in comparison with other methods of obtaining the same information, is given. It is concluded that the greatest promise for future experiments lies in the last category mentioned.