D20 high-flux two-axis neutron diffractometer

Abstract

The monochromatic beam of D20 has a high flux of up to 6 x 10 7 n cm −2 s −1. The two monochromators, HOPG (0 0 2) plus graphite filters and Cu (2 0 0), are vertically focusing and give wavelengths from λ = 0.8 to 2.5 A ̊ . The position-sensitive detector (PSD) has an aperture of 160° with 10 cells per degree (2θ) with ‘microstrip’ detection electrodes. The 1600 cells are connected to 1600 amplifiers, followed by anti-coincidence logics and a fast data acquisition system (DAS) with parallel input. This parallelism allows counting rates up to 50 000 s −1 per cell. High flux and the stationary large PSD permit numerous short-time measurements as used for investigation of phase transitions (thermodiffractometry), kinetic studies, etc. The DAS allows stroboscopic measurements. The time resolution is about 15–40 μs. Due to the high counting rate, a high precision of intensity is obtained by long measurements as used for studying disordered systems and physisorption.