PARITY NONCONSERVATION IN NEUTRON RESONANCES IN TH-232

Parity nonconservation (PNC) was measured for 24 p-wave resonances fro m 8 to 300 eV in Th-232 by measuring the helicity dependence of the to tal neutron cross section for epithermal neutrons with an improved exp erimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all posi tive, thus confirming the previously observed sign correlation. The da ta are fit to the sum of two terms, a constant asymmetry and a fluctua ting asymmetry. With this ansatz the root-mean-square PNC matrix eleme nt M = 1.12 meV, which corresponds to a weak spreading width Gamma(w) = 4.7 x 10(-7) eV. For the neighboring nuclide U-238 there is no const ant offset, suggesting that the sign correlation is specific to Th-232 .