Second‐Order Doppler Shift of Fe57 Mössbauer Resonance in Al‐0.01% Fe57 Alloy Solid Solution

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Abstract
The Mössbauer effect of Fe57 in aluminum was measured over a temperature range from 4.2 °K to 453 °K, using a specimen of supersaturated solid solution of Al‐0.01% Fe57 alloy. From the temperature dependence of the Mössbauer peak position, the second‐order Doppler shift and the isomeric shift of Fe57 in aluminum were estimated separately from the observed total shifts assuming the isomeric shift to be temperature independent. The estimated temperature independent isomeric shift was (0.52 ± 0.02) mm/s relative to metallic iron, somewhat different from the usual room temperature value of (0.43 ± 0.02) mm/s. The temperature dependent second‐order Doppler shift was analysed by the recent Mannheim's expression and the Debye formula. The best fitted force‐constant ratio, λ′/λ, for the iron atom in aluminum host lattice was estimated to be 0.5 < λ′/λ < 1. The zero point kinetic energy of Fe57 in Al was also evaluated by differences between the shifts at 4.2 °K and those at high temperatures.