Capture reactions

Abstract

Capture reactions will be considered here from the viewpoint of the nuclear spectroscopist. Especially important to him are the capture of neutrons, protons, and alpha particles, which may proceed through narrow resonances, offering a well defined initial state for the subsequent deexcitation process. Each of these particles mentioned above has its own advantages and disadvantages, largely depending on particle energy and on the mass number region in which one is going to work.

The γ-radiation produced at a resonance may be investigated through measurements of the γ-ray spectrum and its angular distribution, and through coincidence and angular correlation measurements. The theory is well established, and has been fully supported by experiment in a large number of cases. Complications in the interpretation may arise from interference between different resonances (if these are broad), and from mixing of different channel spins, of different orbital momenta of the incoming particle, and of different γ-ray multipolarities.

Very fruitful have proved (p, γ) reactions on light elements. They offer an almost ideal opportunity for spin and parity determinations of resonance levels and lower levels. From γ-ray intensities it may be possible to test isobaric spin selection rules for E 1 radiation, or, inversely, to determine isobaric spins.