R.C. Byrd

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.

Source properties of intermediate mass fragments emitted in the 270 MeV3He + 232Th reaction☆

Abstract Triple coincidences between intermediate mass fragments (IMFs) and angle-correlated fission fragments were measured in the 270 MeV 3 He + 232 Th reaction. These measurements demonstrate that on the average IMF emission occurs prior to fission from a source which carriers 75–80% of the beam momentum. It was deduced that the average number of IMFs per fragmentation event is close to unity. The dependence of the fission probability on the IMF emission angle and atomic number suggests that fragments emitted at forward angles come from more peripheral collisions than those emitted at very backward angles.

Gamow-Teller strength distribution in 81Kr and the consequences for a 81Br solar neutrino detector

Abstract Neutron time-of-flight measurements have been performed on the 81 Br(p,n) 81 Kr reaction at E p = 190 and 200 MeV. Gamow-Teller transition strengths have been deduced for final 81 Kr states accessible through solar neutrino capture on 81 Br. For the standard solar model, 81 Br is most sensitive to 8 B neutrinos, not — as previously believed — 7 Be neutrinos.