f Measurements with Black Absorbers

Abstract

The Mössbauer fraction f of emitted or absorbed gamma radiation intensity is simply related to the localization of the atom in its host material, and it can in principle be analyzed in terms of the atomic force constants and lattice vibration spectra. As is often the case with measurements of radiation intensities, f is difficult to measure with precision. The measurement requires that one compare the intensity in a very narrow energy interval with the total in a much more diffuse part of a characteristic gamma ray. In the case of Fe⁵⁷, the sharp fraction has energy within a range of about 10⁻⁶ eV at 14 keV, while the intensity of the recoil radiation has a spread of 0.1 eV; this comparison must be made in the presence of other direct and indirect gamma rays and X rays. The situation with respect to the 14-keV Fe⁵⁷ gamma ray is illustrated in Fig. 1. Insert A shows a very simple example of a possible Mössbauer spectrum: two lines of unequal intensities, well resolved by a spacing greater than their natural widths. We must compare the intensity in these two lines with the more diffuse recoil radiation, as shown in Fig. 1B. Both components of the primary 14-keV gamma ray are only a portion of the total primary spectrum of other gamma rays and X rays, shown in C.

This work has been supported by the Air Force Office of Scientific Research, Grant AF-AFOSR-594-64.