Total external reflection of gamma-rays and mössbauer spectroscopy

TLDR: Guides for γ-rays can be constructed by using total external reflection as mentioned in this paper, which can be used to determine the transmission vs. position, as a source was moved across a diameter, provided a technique that greatly helped adjustment of successive sections to colinearity.

Abstract: Guides for γ-rays can be constructed by using total external reflection. Radiation incident at grazing angles less than a critical angle θc ≈ λ (Nee2/πmec2)1/2 may be nearly completely reflected depending upon the surface quality and the absorption coefficient. Sample guides have been constructed from long small-diameter glass laboratory tubing of good straightness. Determination of the transmission vs. position, as a source was moved across a diameter, provided a technique that greatly helped adjustment of successive sections to colinearity. Observation of an unbroadened 57Fe γ-ray resonance between a source and absorber separated by such a γ-ray guide demonstrated that the reflection process is essentially elastic. Computer calculations have analyzed the properties of guides of square cross-section which would be assembled from plates of float glass supported in a vacuum pipe. A large guide constructed in this way could facilitate an improved measurement of the gravitational red-shift. The proportionality to λ2 of the effective aperture of capture by a guide gives to it the properties of a low-pass filter. A bundle of small capillary tubing placed between a source and a detector resulted in a striking reduction in the intensity of high energy radiation reaching the detector relative to that of low energy. Use of lead glass reduced the direct penetration of the high energy γ-rays through the glass and also increased the aperture for low energy by increasing the critical angles.