Single-particle parity-nonconserving matrix elements in 207Pb

Measurements of the helicity dependence of neutron scattering off of heavy nuclei by the TRIPLE collaboration have yielded multiple parity-nonconserving asymmetries. The asymmetries are predominantly positive, in contradiction to the zero average asymmetry predicted by the statistical model of neutron- nucleus scattering. Theoretical calculations that explain the non-zero average asymmetry require single-particle parity- nonconserving matrix elements 10-100 times larger than those predicted by meson exchange models. We are determining the single-particle parity non-conserving mixing in 207Pb by measuring the circular polarization of the 1.064 MeV γ ray. The experiment uses a transmission polarimeter and a fast data acquisition system. Initial results are presented