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An investigation into the Mossbauer effect in Fe57

University of British Columbia

In this thesis the Mossbauer effect in metallic iron has been studied as a function of the length of time of diffusion of the Co⁵⁷ source into metallic iron, of the source temperature over the range 156°K to 478°K, and of the absorber thickness. In each case, the line shape, width, intensity and shifts were measured. Measurements showed that the appearance of an appreciable Mossbauer effect, .122, arises within the first ten minutes of diffusion time at 900°C in a hydrogen atmosphere and that additional time is required to reduce the line width and to increase the intensity to .145. The observed temperature shift of the resonantly absorbed 14.4 kev radiation followed that which was predicted by the Josephson effect. However, corrections for an isomer and a hydrostatic compression shift were made to the data before comparing the measured shift with the theoretical shift. The results indicated a Debye temperature of Θ[subscript D] = (420±20)°K for both the source and absorber used. The measurements made over the temperature range indicated that the internal magnetic field H̰ followed the saturation magnetization curve (the Weiss Law) closely. For small temperature differences between the source and absorber, ΔΘ < 50°K, measurements were made indicating that the minimum line width occurred at ΔΘ = 24°K. These results indicated that the internal magnetic field at ΔΘ = 0°K for the source was .01x10⁵oe greater than that of the absorber. For ΔΘ ≥ 100°K, the Mossbauer line displayed a hyperfine structure arising from the temperature dependent difference in the internal magnetic field at the nuclei. The line profile, width, shift and intensity were measured for four absorber thicknesses - .0002", .00035", .00055", and .001". The detailed comparison of these line characteristics with the theoretical values required an extension of existing treatments, a discussion of which is given in chapter five. In each case it was observed that the Mossbauer line was accompanied by two small peaks, one on either side of the main line. The position of these peaks indicated that they were associated with a small or zero internal magnetic field at the site of some of the Fe⁵⁷ atoms.

Text

2011-12-15

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http://hdl.handle.net/2429/39704

Physics

University of British Columbia

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