A test of time-reversal invariance was performed by measuring the imaginary part $\left|\delta \right|sin\eta$ of the mixing ratio $\delta =\left|\delta \right|e^{i\eta }$ between $E2\mathrm{}$ and $M1\mathrm{}$ reduced matrix elements through the observation of two $\beta -\gamma -\gamma$ cascades in ${}_{}{}^{56}{}_{}{}^{}\mathrm{Mn}$. The imaginary part was found to be (-8.1±4.8)×${10}^{-3\mathrm{}}$ for the 1.81-MeV transition, and (-7.1±3.7)×${10}^{-3\mathrm{}}$ for the 2.12-MeV transition. In order to eliminate instrumental asymmetries, the difference between the two values was taken, $\Delta \mathrm{}\left(\right|\mathrm{}\delta \left|sin\eta \right)=(1\mathrm{}\pm 6)\times {10}^{-3\mathrm{}}$. With an average mixing ratio for the two transitions, $〈\left|\delta \right|〉=0.24\mathrm{}$, the difference in phases is $\Delta sin\eta \approx \Delta \eta \approx (0.4\mathrm{}\pm 2.6)\times {10}^{-2\mathrm{}}$, giving no evidence for time-reversal violation.

• Received 19 June 1969

DOI:https://doi.org/10.1103/PhysRev.187.1410