Optimisation of Analyser Geometry for a Near Back-Scattering Spectrometer: IRIS211 on the ISIS Pulsed Source

摘要

The report describes the upgrade of the pyrolytic graphite (PG) analyzer bank on211u001ethe IRIS high-resolution inelastic spectrometer at ISIS from 1350 graphite pieces 211u001e(6 rows by 225 columns) to 4212 crystal pieces (18 rows by 234 columns). The new 211u001eanalyzer array will achieve a three-fold increase in area and in addition the 211u001egraphite crystals will be cooled close to liquid helium temperature to reduce 211u001ethermal diffuse scattering, thereby furter improving the sensitivity of the 211u001espectrometer. For an instrument such as IRIS, with its analyzer out of exact back-211u001escattering geometry, optical aberration and variation in the time-of-flight of 211u001ethe analyzed neutrons is introduced as one moves out from the horizontal 211u001escattering plane. To minimize such effects, the profile of the analyzer array has 211u001ebeen redesigned. The concept behind the design of the new analyzer bank and the 211u001efactors that effect the overall resolution of the instrument are discussed.