The (p, n) reaction as a probe of beta decay strength

The evidence for a useful proportionality relationship between 0° (p, n) cross sections and the corresponding Gamow-Teller and Fermi beta-decay transition strengths is examined in detail. A simple parameterization for small momentum transfer L = 0 transitions is developed and used in the analysis of (p, n) data in the bombarding energy range 120–200 MeV. The parameterization describes the (p, n) differential cross section in terms of momentum transfer, energy loss, mass number, and bombarding energy and provides a straightforward way of extrapolating to zero momentum transfer. It is found that a single proportionality constant can serve to relate all Gamow-Teller transitions originating from the same target nucleus. The target dependence of this proportionality constant, however, is found to be unpredictable at the 20%–50% level, even within isotopic chains. Such large variations cannot be easily explained in the context of the standard single-step direct-reaction distorted-waves impulse approximation model.