Unless parity conservation breaks down in strong interactions the radiations emitted from an isolated level cannot display odd powers of $cos\theta$ in their angular distribution or correlation. A search for such powers is then an approach to the conservation problem. The ½- first excited state of ${\mathrm{Li}}^7$ at 477 kev has been excited by inelastic proton scattering. The expected angular distribution of the gamma rays of de-excitation relative to the bombarding proton beam is $1+\alpha cos\theta$ where $\alpha$ is of order $\mathcal{R}{\mathfrak{F}}^2$, $\mathfrak{F}$ being the amplitude of the parity nonconserving part of the relevant wave functions and $\mathcal{R}$ is a matrix element factor. By comparison with the radiation following $K$ capture in ${\mathrm{Be}}^7$ it is shown that $\alpha$ is zero within a standard deviation of 6 parts in ${10}^4$. This corresponds to ${\mathfrak{F}}^2\lesssim 1\times {10}^{-4\mathrm{}}$.

• Received 22 October 1957

DOI:https://doi.org/10.1103/PhysRev.109.1614