Realization of wide angle NSE: The spectrometer SPAN

Abstract

Simultaneous measurements over a large angular range are commonly used to improve the data acquisition rate of neutron spectrometers. Almost thirty years after the discovery of Neutron Spin Echo (NSE) [l], however, all NSE spectrometers, with the exception of INllC [2], are single-detector type. This is due to the strict conditions for the homogeneity of the magnetic field integral (10−4 − 10−5) along all neutron trajectories. A substantial enhancement of the NSE data collection rate has been achieved with the magnetic field configuration of the spectrometer SPAN at BENSC. We developed a novel setup with cylindrical symmetry, which allows for NSE data to be taken simultaneously over the whole range of scattering angles accessible by a spectrometer, typically from −150° to 150°. The high symmetry and homogeneity of the magnetic field configuration allows for using a large incoming beam cross section, of actually 58 mm × 100 mm on SPAN, and a large vertical beam divergence of up to 3°, leading to a most efficient use of neutrons and to a substantial improvement of the data acquisition rate.