Laue Diffractometer at a Long Pulse Spallation Source

The performance of a Laue diffractometer at a Long Pulse Spallation Source is illustrated by an example. The instrument is built at a thermal f = 25 Hz source and uses a neutron guide, which is 70m long, and a wavelength band of 2 Å at the position of the sample. The pulse of 2ms of the source can be chopped to provide a variable resolution of the order δλ/λ = 1–3%. The instrument is suited for the investigation of samples with unit cell volumes of the order of 100–1000 ų at a medium time resolution. For an averaged spallation beam power of 5MW the neutron flux at the sample position is estimated to amount to Φ = 3–8 × 10⁷ n cm⁻² s⁻¹, depending on the chopper speed. The performance of the instrument is demonstrated by a Monte Carlo simulation technique. Calculations with an idealised model sample focus on the peak-to-background ratio and the ability to resolve Bragg peaks.