Added precision in 57Fe Mossbauer spectroscopy

Abstract

This paper contains (1) the necessary mathematics for a precise interpretation of Mossbauer data, and (2) a characterization of a spectrometer designed specifically to maximize the information avalable from these data. The innovative aspects of this spectrometer are that it provides a known absorber lineshape, that it is quantitative, and that is provides information of the vibrational states of the absorber via the second order Doppler shift vs temperature and the total absorption vs temperature. The spectrometer allows sample temperature and applied magnetic field to be varied in any combination of 2-350 K or 0-6 T, respectively. Simultaneous collection of four data streams allows an accurate representation of the transmission spectrum. Sophisticated computer treatment with extensive use of least squares fitting procedures and fast Fourier transform techniques provides the final output display of sample cross-section vs standardized source velocity. The cross-section display is shown to be independent of the thickness of samples with Mossbauer optical densities up to 3. In addition, we report the method and results of measurements which must precede the operation of the spectrometer: (1) the absorption coefficient of iron at 14 keV: (498+/-7)cm-1, (2) the Debye temperature of our source (57Co in rhodium matrix): (361+/-20)K, (3) the source lineshape: three Lorentzians with Heisenberg linewidth, a center line with twice the intensity of the symmetrically placed outer lines which are spaced 0.055 mm/s apart, (4) the Mossbauer effect cross-section for 57Fe: (2.4+/-0.2) x 10-18 cm2, (5) the Debye temperature of iron (NBS # 1541): (430+/-30) K, and (6) the values for the Hamiltonian parameters of iron metal (NBS # 1541) at 290, 101 and 4.2 K. The precision of the determined Hamiltonian parameters is defined in terms of a statistic with a weighted [chi]2 distribution.