Multi-wavelength data collection strategies in inelastic neutron scattering

Abstract

The overwhelming tradition in neutron-scattering research was the use of a monochromatic incoming beam with a single wavelength for essentially all kinds of experiments, with only a very few exceptions in the practice at continuous neutrons sources. The situation dramatically changed with the spread of pulsed spallation sources, where the wavelength scanning “energy dispersive” time-of-flight approach is the natural rule in all diffraction type work and in inverted geometry inelastic spectroscopy. In recent years, a number of new applications of multi-wavelength data collection strategies emerged in inelastic neutron spectroscopy, both at continuous and pulsed sources. The aim of the present paper is to review these developments. Time-of-flight (TOF) and Neutron Spin Echo (NSE) lend themselves most easily to such methods, since they allow rather exact comparison of absolute scattering intensities measured at different instrumental configurations. The use of multiple wavelengths can offer different kinds of advantages in neutron spectroscopy. Since the resolution of spectrometers rapidly changes with the wavelength, its variation can be effectively used to extend the available dynamic range. Inelastic multiple scattering effects can be precisely identified and corrected for by their inherently strong wavelength dependence. At pulsed spallation sources the multi-wavelength approach opens up the way to enhance data collection rates by eliminating at least a large part of the dead time between too distant source pulses.