ELECTRIC-FIELD GRADIENT SIGN DETERMINATION IN LOW MAGNETIC-FIELDS PERPENDICULAR TO THE GAMMA-RAYS IN FE-57 MOSSBAUER-SPECTROSCOPY

The determination, by Mossbauer Fe-57 spectroscopy, of the sign and the asymmetry parameter of the electric field gradient (EFG), in a non-magnetic powder sample, needs the use of an external magnetic field. Usually a "parallel-magnetic-field-to-the-gamma-rays" configuration is employed. In the present work, theoretically generated spectra in both configurations, parallel an perpendicular, are compared. The result is that the spectra in the perpendicular configuration show always a larger asymmetry for the same fields intensities. In consequence, the sign determination of the EFG, is possible with magnetic fields significantly smaller in the perpendicular case than in the parallel one. Furthermore, the practical consequences are important, because EFG studies with conventional electromagnets, allowing only fields lower than 25 kGauss are feasible. As an example, Mossbauer experimental results obtained at room temperature for natural pyrite (FeS2) in perpendicular fields of 15 and 20 kGauss, created by a conventional electromagnet, are shown here.