Abstract
The thickness dependence of the Mossbauer absorption in single crystals of monoclinic Fe(NH4)2(SO4)2.2H2O has been studied. A redetermination of the orientation of the electric field gradient tensor at the iron resolves the contradictions in previously published data. The value of the asymmetry parameter at 295K is close to unity, and the first excited electronic state is at 135+or-15 cm-1 above the ground state. A twin-crystal experiment was devised to give additional polarization data in the plane normal to the axis of observation.