Direct Nuclear Reactions

It is the contention of this paper that the large majority of nuclear reactions which proceed to a low-lying level of the final nucleus are predominantly direct reactions with stripping-like angular distributions. It is seen that reactions of the form ($n, p$), ($p, p^{\prime }$), ($\alpha , {\alpha }^{\prime }$), ($\alpha , p$), etc. have essentially as much chance of proceeding directly as does the deuteron stripping or pickup reaction. This latter reaction no longer appears in a category of its own, but merely as one example of a whole gamut of types of reactions which proceed via a characteristic direct process. Differential cross sections for the general class of direct reaction are calculated, and closed-form expressions obtained by means of the same approximations originally employed for the deuteron stripping reaction. It is seen that the angular distributions are dependent on the spins and parities of the initial and final nuclei involved, and are thus capable of yielding information regarding these properties; moreover the absolute magnitudes are capable of yielding interesting information concerning nuclear structure. Comparisons between theory and experiment are made for a few typical reactions.