Experimental detection of specular reflection of $\gamma$ quanta

Scattering of bremsstrahlung electron beam ($E_e$ = 6.25 MeV) collimated with a vertical divergence $\delta\gamma\approx\pm$ 60 $\mu$rad and incident on the mercury surface at glancing angles $\alpha$ = -37, -83, and -140 $\mu$rad is studied on the 118-m-long path length. The specular reflection effect is detected in the spectral and angular distributions of $\gamma$ quanta with energies up to 3 MeV. The reflection coefficients vary from 0 to $\sim$17% depending on the angles of incidence and the $\gamma$ quanta energy.