The presence of the stable isotope 57Fe to an abundance of 2.2% in all natural compounds of iron makes it possible to study hemoglobin by the methods of Mossbauer spectroscopy (Wertheim, 1964; Greenwood and Gibb, 1971). In such experiments a sample of hemoglobin is exposed to a beam of highly monochromatic γ rays emanating from a radioactive source which contains 57Fe nuclei in an excited state (as a daughter product of 57Co). When the radioactive 57Co is embedded in any one of a number of solid matrices, the γ ray line is so narrow that its energy can easily be shifted several linewidths by means of the Doppler effect, that is, by oscillation of the source (or absorber) at moderate velocities. The velocity drive which provides a Doppler shift to the γ ray photons is therefore the analog of the dispersive device such as a prism or grating in optical spectroscopy. At certain velocities corresponding to shifted γ ray energies the absorption of γ photons in 57Fe nuclei (contained in hemoglobin) is accompanied by transitions from the nuclear ground state to the first excited state. A plot of the transmitted γ ray intensity as a function of Doppler velocity constitutes a Mossbauer spectrum in which characteristic absorptions are observed as a decrease in transmitted intensity at certain velocities. The convention is to consider the velocity as positive when the source and absorber are in relative motion toward each other.
KeywordsMossbauer Spectroscopy Isomer Shift Quadrupole Splitting Electric Field Gradient Magnetic Hyperfine
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