A Simple Monochromatic, Polarized Fe57 Mössbauer Source
The use of a polarized gamma-ray source in Mössbauer experiments leads to a significant simplification of complex spectra and the possibility of obtaining information not otherwise easily available. Polarization effects must be considered in all studies utilizing the intensities or relative intensities of absorption lines, such as finding the orientation of EFG tensor, mean-square displacements, magnetic structure, and powders with quadrupole effects in external magnetic fields.
Previous attempts to produce a polarized source have been expensive or cumbersome and did not always produce a monochromatic beam. One technique is to use radiation scattered from a magnetized foil. This is wasteful of source intensity. A second is to magnetize the source, producing several lines of definite polarization. The most promising approach is to use a filter. Thus far, that has meant moving an absorber at a constant velocity with respect to the source such that one polarization is absorbed by it and the other is allowed to pass to the absorber sample of interest. Until now, this has required two driving systems.
The recent availability of the source Co57 in CoO for use in the MOssbauer spectroscopy of iron has made possible the following development. The isomer shift of this material is on the order of — 1.0 mm/sec with respect to metallic iron, thus placing the right peak of the inner pair of the absorption spectrum of iron very nearly at zero velocity. Alloying iron with rhodium at a certain composition has produced a material one of whose absorption peaks is at zero velocity and is broad enough to cover the source line. When this material is attached to the source and suitably magnetized, a beam of monochromatic radiation of almost 100% linear, left or right circular, or elliptical polarization (depending on the orientatation of the magnetization) is produced.
Several spectra have been taken as examples and are presented. Other studies which will utilize this source are in progress.
KeywordsIsomer Shift Source Line Electric Field Gradient Metallic Iron Fe57 Nucleus
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