Application of M\"{o}ssbauer spectroscopy to study vibrations of a granular medium excited by ultrasound
It is shown that analysis of M\"{o}ssbaur spectra of a granulated medium, immersed into the epoxy resin without hardener, allows to study mechanical vibrations of granules. In our experiments, small particles of the potassium ferrocyanide with a 1.25 micron mean size played a role of granules. This compound was enriched by $^{57}$Fe isotope. Particle vibrations in the vibrated resin with the frequency 12.72 MHz were induced by piezo polymer film. At rest, M\"{o}ssbauer spectrum of $^{57}$Fe in the potassium ferrocyanide consists of a single line. Ultrasonic vibration of nuclei splits the line into a comb structure with a period equal to the vibration frequency. The spectrum analysis allows to estimate the vibration amplitude of particles and decay of the ultrasound in this medium. The proposed method is unique since it allows to measure subangstrom displacements of particles vibrating with several MHz frequency.