Polarized radiation in Mössbauer spectroscopy

Mössbauer polarimetry is a spectroscopic technique sensitive to the orientations of hyperfine fields. The technique is particularly effective with monochromatic, polarized radiation: the measured spectra do not contain many additional transitions present when nonmonochromatic radiation is used. The paper reviews recent achievements in the construction of sources of polarized monochromatic radiation. Recently, filter techniques were adopted for achieving circularly and linearly polarized radiation from commercially available radioactive isotopes. A synchrotron source with nano-eV energy width, suitable for Mössbauer measurements was constructed. Applications are reviewed, in particular determination of the direction of the hyperfine magnetic field and the orientation of the electric field gradient. Special attention is paid to cases when the distributions of the hyperfine fields and mixed interactions result in poorly resolved spectra. Recent achievements in methodology are described. An explicit form of the intensity tensor is derived, which allows the transition probabilities to be calculated omitting the diagonalization of the Hamiltonian. The concept of the velocity moments is introduced. It is shown that some averages of the whole Mössbauer spectra relate to the averages of hyperfine fields and possess tensor properties.