Interference between Rayleigh and nuclear resonant scattering of γ-rays

Abstract

The possibility of observing interference between nuclear resonant scattering and Rayleigh scattering of y-rays is examined with reference to (1) thermally broadened medium -energy lines such as the 411 keV E 2 line of 198 Hg, (2) recoil-broadened lines of substantial natural width, for example, the 986 keV E l transition in 152 Sm, (3) lines of natural width only, as in 57 Fe. For the first two examples, where the incident spectral distribution is not of simple form, a graphical method shows that the interference term is small in comparison with the others whenever the resonant scattering is itself a substantial effect, even if full coherence exists between the resonant and Rayleigh components. It remains possible that interference may be observable in other examples of the second class, to which the graphical method could be extended. For the third class, an analytical approach is adopted and leads to the conclusion that coherence should be only partial, in the sense that part of the resonant scattering reflects the character and preserves the phase of the incident radiation, as does the Rayleigh scattering, while part is characteristic of the resonator and has no counterpart in the Rayleigh scattering. If the incident line is far off resonance these two parts of the resonance radiation will have distinctly different frequencies, a single incident line giving a scattered doublet. In some circumstances, interference with Rayleigh scattering may aid the observation of a weak resonance against a strong background