In 90° scattering of 14.4-keV $\gamma$ rays from ${\mathrm{Fe}}^{57}$, we have observed several percent difference in the intensities of the conjugate lines in the six-line hyperfine spectrum depending on the vectorial relations between the wave vectors for the incident $\gamma$ ray ${\overrightarrow{\mathrm{k}}}_i$, the outgoing wave vectors ${\overrightarrow{\mathrm{k}}}_f$, and the magnetic induction field $\overrightarrow{\mathrm{B}}$. The intensity of the line corresponding to the $m=\frac{1}{2}\to \frac{3}{2}\to \frac{1}{2}$ transition differs from that of the conjugate transition $m=-\frac{1}{2}\to -\frac{3}{2}\to -\frac{1}{2}$, by +6.8 ± 2.4%. Intensity differences are also found between the $m=\frac{1}{2}\to -\frac{1}{2}\to (\frac{1}{2},-\frac{1}{2})$ line and its conjugate transition (-6.0 ± 3.5%). The sign of these asymmetries depends on whether ${\overrightarrow{\mathrm{k}}}_i\times {\overrightarrow{\mathrm{k}}}_f$ is parallel or antiparallel to the internal magnetic field $\overrightarrow{\mathrm{B}}$. It is likely that these asymmetries result from interference between electronic (Rayleigh) scattering and nuclear resonant scattering. The signs and the calculated values for the asymmetries based on theory agree with the observed values.

• Received 9 August 1971

DOI:https://doi.org/10.1103/PhysRevC.6.836