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How can single crystals be used to measure atomic motion in specific directions?

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Figure 1: Spectrometer utilizing Mössbauer effect concept Effect is usually observed by measuring transmission of gamma rays from radioactive source through absorber containing resonant isotope. — Mössbauer effect Figure 1: *Spectrometer utilizing Mössbauer effect concept* Effect is usually observed by measuring transmission of gamma rays from radioactive source through absorber containing resonant isotope.

In the study of lattice dynamics, the Mössbauer effect allows for the precise measurement of atomic motion. The probability of a recoil-free gamma-ray emission depends on the amplitude of thermal vibrations relative to the gamma-ray wavelength. By measuring the fraction of these recoil-free events—determined by the ability of the gamma rays to be resonantly absorbed—researchers can calculate the mean square amplitude of thermal motion within a solid.1

When using single crystals, this technique enables the measurement of the amplitude of atomic motion in specific crystallographic directions. These measurements provide a stringent test for various lattice dynamical models, allowing physicists to observe how atoms vibrate along particular axes within the crystal structure.1