Anomalous transmission of Mossbauer radiation in pure nuclear Laue diffraction. III. Anisotropic scattering

Abstract

For pt.II, see ibid., vol.19, p.2567 (1986). The angular dependence of the anomalous transmission of polarised Mossbauer radiation through a perfect single-crystal platelet of ⁵⁷FeBO₃ was studied. Rocking curves of the Laue reflected and of the Laue transmitted beams were simultaneously recorded for the pure nuclear reflection (001). Striking asymmetries were observed between the transmitted and the reflected intensities for the two polarisation components. The asymmetries were caused by the strong anisotropy of the nuclear resonance scattering. The asymmetry between the total intensities (transmitted plus reflected beam) for the two polarisation components was related to a strongly asymmetric division of the incident radiation into the two wavefields built up inside the crystal. The asymmetry between the intensities of the transmitted and reflected beams revealed a strongly asymmetric composition of the wavefield experiencing anomalous low resonance absorption. The observed anomalous transmission of such a strongly asymmetric wavefield uniquely demonstrated the origin of the suppression of the incoherent reaction channels, i.e. the cancellation of the total amplitude for the individual nuclear excitation (the Kagan-Afanasev rule) rather than the cancellation of the total amplitude of the radiation field at the nuclear position.