Energy Resolution and Focusing in Inelastic Scattering Experiments

Abstract

In elastic scattering experiments, it is appropriate to consider the scattering pattern in the space of momentum and energy transfers, and a proper treatment of resolution takes account of momentum and energy together, both as regards the correlation of momentum and energy increments in the beams of incident and scattered particles and as regards the structure of the cross section under observation. A description is given of the calculation of resolution widths in measurements on a phonon dispersion surface with a three‐axis crystal spectrometer, and of the manner in which the two main contributions to the energy resolution width may be minimized by focusing— which involves a suitable choice of the monochromator and analyser crystals, the beam path, and the incident and scattered energies. Focusing usually improves resolution markedly without loss of intensity, and often with a gain in the peak intensity of a recorded resonance. An experimental illustration is given. Cases where focusing entails loss of intensity are discussed in connection with intensity formulas.