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

A M\"ossbauer-effect experiment, with {γ}-ray wave vector k directed both along and normal to the c axis of a siderite (FeCO₃) single-crystal platelet, has been systematically performed in the temperature range 50T300 K. The T dependence of the integrated area S(T)=S_π(T)+S_σ(T) under the quadrupole doublet reveals that at 300 K the Debye-Waller factors are fc=0.72(2) and f_⊥c=0.75(2). Independently, the area ratios S_π/S_σ under the {π} and {σ} 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.