Weak interaction theories of the "current-current” form predict a weak parity-non-conserving force between nucleons. One manifestation of such a force is the net circular polarization of γ rays from unoriented nuclei. We have measured the circular polarization for four favorable nuclear γ transitions obtaining
180Hf 501 keV γ: pγ = (-23 ± 6) x 10-4
159Tb 363 keV γ: pγ = (-1 ± 5) x 10 -4
203Tl 279 keV γ: Pγ = (-0.04 ± 0.10) x 10-4
181Ta 482 keV γ: pγ = (-0.031 ± 0.025) x 10 -4
The measurements were performed with a forward-scattering rapidly reversing Compton polarimeter and a phase-sensitive detection system. The analyzing efficiency of the Compton polarimeter, including effects of multiple scattering, was determined by Monte Carlo calculations. It was necessary in most experiments to apply corrections for polarized bremsstrahlung associated with β decays. Calculations of bremsstrahlung effects were verified by experiments on 198 Au and 177Lu. The residual asymmetry of the polarimeter itself was determined by contro1 experiments on103Ru.
The values of Pγ obtained are compared with related experiments and discussed in the framework of nuclear and weak-interaction theories.
