Mössbauer surface-guided waves in media with space modulation of Mössbauer isotope concentration.

Rapid progress in Mössbauer spectroscopy combined with synchrotron radiation (SR) makes it urgent to study the interaction of SR with structures which have a space modulation of the Mössbauer isotope concentration, and thereby to reveal new effects in this interaction. Presented here are theoretical studies of the Mössbauer surface-guided mode (MSGM) in such media. MSGMs are analogous to the well known surface-guided electromagnetic waves (SGEW) in periodic media. However, because of their resonant interaction with Mössbauer nuclei they reveal some qualitative peculiarities compared with the case of conventional SGEW. The MSGMs for the case of purely nuclear Bragg scattering of quanta at a plane interface between a homogeneous medium and a medium with a periodic space modulation of the Mössbauer isotope concentration are investigated theoretically. The conditions of MSGM existence and allowed spectral intervals for the MSGM and their dependence on the period of space modulation and the degree of medium enrichment by the Mössbauer isotope are found. It is shown that the allowed interval of the MSGM frequencies is located at one side relative to the exact Mössbauer resonant frequency. Its width is of the order of the Mössbauer line width and can be effectively changed by the variation of the modulation period or the Mössbauer isotope concentration. For the MSGM frequencies close to the boundary of the MSGM existence interval, the attenuation of an MSGM propagating along the interface may be essentially lower than the conventional Mössbauer radiation attenuation in the same medium. The possibilities of SR Mössbauer filtration by means of MSGM are briefly discussed.