Parity Violation in Neutron Capture Reactions

In the last decade, the scattering of polarized neutrons on compound nucleus resonances proved to be a powerful experimental technique for probing nuclear parity violation. Longitudinal analyzing powers in neutron transmission measurements on p-wave resonances in nuclei such as La and Th were found to be as large as 10%. Here we examine the possibilities of carrying out a parallel program to measure asymmetries in the (n, γ) reaction on these same compound nuclear resonances. Symmetry-violating (n, γ) studies can also show asymmetries as large as 10%, and have the advantage over transmission experiments of allowing parity-odd asymmetries in several different gamma-decay branches from the same resonance. Thus, studies of parity violation in the (n, γ) reaction using high efficiency germanium detectors at the Los Alamos Lujan facility, for example, could determine the parity-odd nucleon-nucleon matrix elements in complex nuclei with high accuracy. Additionally, simultaneous studies of the E1 and VPNC matrix elements involved in these decays could be used to help constrain the statistical theory of parity non-conservation in compound nuclei.