A One-Sided View of Mössbauer Spectroscopy
Most Fe57 Mössbauer spectra are obtained with transmission geometry. The thickness of the sample is chosen to limit photoelectric absorption at 14 keV to 10 to 90%. There are, however, many objects whose Mössbauer spectra could be usefully analyzed but which do not satisfy the transmission requirements. These include massive items such as lathe beds and irregular items such as ball bearings. The physics of a one-sided spectrometer are simple; the resonant capture of. a 14-keV gamma ray within the sample results in either a reemitted 14-keV gamma ray (9% probable) or internal conversion leading to iron X rays and a conversion electron (91% probable). A counter, shielded from the direct rays of thesource, intercepts the 6-keV X rays from the sample. The Mössbauer spectra are inverted, i.e., they result in enhanced count rates. Instrumental problems are severe since the effect is only 10% as large as one obtains in transmission. Two types of spectrometers will likely emerge, scanning and nonscanning. The nonscanning type is similar to nondispersive analyzers in that the sources are chemically or thermally tuned in lieu of Doppler shifting. Areas of application include the determination of phases in steels, the nature and kinetics of corrosion, and possibly surface stresses in ferritic steels.
KeywordsFerritic Steel Internal Conversion Armco Iron Transmission Geometry Internal Magnetic Field
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