Time Dependence of Mössbauer Scattered Radiation

Time distributions of resonantly scattered 14.4-keV ${\mathrm{Fe}}^{57}$ $\gamma$ rays were measured by using as time-zero signals the preceding 122-keV $\gamma$ rays. A ${\mathrm{Co}}^{57}$ source coplated with Fe was used with two different metallic scatterers (2.54×${10}^{-2\mathrm{}}$-mm-thick 92.8% ${\mathrm{Fe}}^{57}$ and 4.53×${10}^{-3\mathrm{}}$-mm-thick 2.19% ${\mathrm{Fe}}^{57}$) in a cylindrical geometry. Measurements were performed at different relative source velocities. From the measured time spectra, contributions due to random coincidences and to Rayleigh scattering were subtracted. A theory based on a classical model in which the scattering nuclei are represented by randomly situated harmonic oscillators was developed. The experimental results are compared with computed theoretical curves. Good agreement was found in most of the cases. Discrepancies observed in two instances are discussed.