A.M. Afanas'ev

On excitation of isomeric nuclear states in a crystal by synchrotron radiation

The time dependence of delayed radiation is investigated when a pulse of synchrotron radiation undergoes resonance Bragg scattering by the nuclei in a crystal that have an isomeric level with a Mossbauer transition. Instead of the usual exponential law exp(-t/ tau 0) characteristic of an isolated nucleus, a time dependence in the form ( tau 0/t)2 exp(-t/ tau 0) was discovered at small deviations alpha from the Bragg angle. The acceleration of the decay is connected with the collective nature of the excitation of the nuclei in the crystal-the nuclear exciton formation. The exponential law remains at large alpha but the intensity decreases as 1/ alpha 2. In the case of large divergence of the incident beam the law ( tau 0/t) exp(-t/ tau 0) is obeyed. The frequency distribution of the reflected pulse and the possibility of formation of a resonance structure with sufficient resolution are analysed in detail.

The role of lattice vibrations in dynamical theory of X‐rays

A consistent dynamical theory of X-rays is developed which takes into account in explicit form the processes of Thomson scattering, photoelectric absorption, and Compton scattering as well as inelastic scattering of X-rays by phonons. Special attention is paid to analysis of the role played by lattice vibrations and temperature. Owing to inelastic scattering by phonons, the temperature dependence of the coefficients of dynamical equations is not determined by Debye–Waller factors but has a more complicated behaviour. A detailed analysis is given of the influence of lattice vibrations on the effect of anomalous transmission.

Time delay in the resonance scattering of synchrotron radiation by nuclei in a crystal

Abstract The time dependence of delayed radiation has been found when the pulse of synchrotron radiation undergoes the resonance Bragg scattering by nuclei in a crystal that have an isomeric Mossbauer level. A strong acceleration of the discovered is connected with a collective character of the nuclear excitation. A possibility to conserve the angle direction as well as the intensity and the resonance structure in the delayed reflected radiation is analysed.

Interference of nuclear resonance electron production and photoeffect for Mössbauer E2 and M1 γ-rays

Abstract It is shown that this type of interference can display itself for E2 and M1 nuclear transitions if one studies the angular distribution of the electron produced by the γ-rays rather than the total absorption.

On the lineshape of spin-relaxation broadened Mössbauer spectra of some Fe3+ paramagnets

Abstract The spin relaxation broadened Mossbauer spectra of alums and Fe(NO 3 ) 3 ·9H 2 O were studied. A correlation between the different types (α, β) of alums and the characteristics of the spin relaxation has been found.

Analysis of formation of the suppression effect of nuclear reaction. Inelastic channels in the presence of hyperfine splitting

The analysis, carried out in the work, of the emergence of the effect of suppression of the nuclear reaction (ES) during resonance Bragg scattering of Mössbauer gamma-quanto from nuclei under conditions of a hyperfine splitting allows to clearly reveal the fundamental features characteristic of this phenomenon. An is shown in sections 3 and 4, in a general case of realization of ES neither electric nor magnetic vectors of the wave field in the crystal turn to zero at the points of equilibrium positions of the nuclei. For the reaction to be suppressed, it is necessary that the total amplitude of the excited nucleus formation be zero. In this case, a rather peculiar picture of the electromagnetic field within the crystal sets in which depends on the character of the hyperfine splitting and on the multiplicity of the transition. In this work, conditions have been found of the coexistence of ES for both polarizations, and with these conditions being fulfilled, the strongly resonantly absorbing crystal becomes transparent for the whole of radiation. Special attention has been paid to the proof that lattice vibrations do not restore the nuclear absorption of gamma-quanta. It is interesting that all this takes place during resonant interaction with a separate nucleus when the cross-section of the inelastic process may be large as compared with the elastic scattering cross-section. Although all these features (and a number of others discussed in detail in the text) essentially distinguish ES from the Borrmann effect for X-rays, there is a circumstance which makes them related. In both cases it is necessary to produce a coherent superposition of waves within the crystal owning to the Bragg diffraction of the incident quanta, and in the both cases the crystal becomes more transparent for the radiation that comes through.