Experiments on Parity Nonconservation in Nuclear Forces. III. Gamma Transitions inHf180,Tb159,Ta181,Tl203, andW182

We have further studied the parity admixtures in nuclear $\gamma$ transitions by measuring the circular polarization of $\gamma$ rays from five nuclei with a technique different from that of our work I and II in this series. The experiments 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 $\beta$ decays. Calculations of bremsstrahlung effects were verified by experiments on ${}_{}{}^{198}{}_{}{}^{}\mathrm{Au}$ and ${}_{}{}^{177}{}_{}{}^{}\mathrm{Lu}$. The residual asymmetry of the polarimeter itself was determined by control experiments on ${}_{}{}^{103}{}_{}{}^{}\mathrm{Ru}$. The values of $P_{\gamma }$ obtained were ${}_{}{}^{180}{}_{}{}^{}\mathrm{Hf}$ 501 keV, $P_{\gamma }=(-23\mathrm{}\pm 6)\times {10}^{-4\mathrm{}}$; ${}_{}{}^{159}{}_{}{}^{}\mathrm{Tb}$ 363 keV, $P_{\gamma }=(-1\mathrm{}\pm 5)\times {10}^{-4\mathrm{}}$; ${}_{}{}^{203}{}_{}{}^{}\mathrm{Tl}$ 279 keV, $P_{\gamma }=(-0.04\mathrm{}\pm 0.10)\times {10}^{-4\mathrm{}}$; ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ 482 keV, $P_{\gamma }=(-0.031\mathrm{}\pm 0.025)\times {10}^{-4\mathrm{}}$; ${}_{}{}^{182}{}_{}{}^{}\mathrm{W}$ 1189 keV, $P_{\gamma }=(-0.25\mathrm{}\pm 0.40)\times {10}^{-4\mathrm{}}$. A survey and a discussion of these results is presented.