Gamma -ray polarization in transmission through a noncubic and nonmagnetic single crystal.

Abstract

A M\"ossbauer-effect experiment, with \ensuremath{\gamma}-ray wave vector k directed both along and normal to the c axis of a siderite (${\mathrm{FeCO}}_{3}$) single-crystal platelet, has been systematically performed in the temperature range 50T300 K. The T dependence of the integrated area S(T)=${\mathit{S}}_{\mathrm{\ensuremath{\pi}}}$(T)+${\mathit{S}}_{\mathrm{\ensuremath{\sigma}}}$(T) under the quadrupole doublet reveals that at 300 K the Debye-Waller factors are ${\mathit{f}}_{\mathit{c}}$=0.72(2) and ${\mathit{f}}_{\mathrm{\ensuremath{\perp}}\mathit{c}}$=0.75(2). Independently, the area ratios ${\mathit{S}}_{\mathrm{\ensuremath{\pi}}}$/${\mathit{S}}_{\mathrm{\ensuremath{\sigma}}}$ under the \ensuremath{\pi} and \ensuremath{\sigma} quadrupole components, measured at 300 K, confirm the lack of a spatial anisotropy of the f factor but, more significantly, confirm the theoretically predicted polarization-dependent resonant-absorption cross section in transmission through the crystal.