Instrumental design and expected performance of coupled-moderator near-backscattering spectrometer at J-PARC

Takahashi, Nobuaki; Shibata, Kaoru  ; Sato, Taku*; Tamura, Itaru  ; Kajimoto, Ryoichi  ; Harjo, S.   ; Oikawa, Kenichi   ; Arai, Masatoshi; Mezei, F.*

A near-backscattering crystal-analyzer neutron inelastic spectrometer, DIANA has been proposed to construct at Materials and Life Science Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). It has firstly been designed to see a decoupled non-poisoned moderator in order to obtain higher intensity and better energy resolution. In deed, the decoupled moderator has a narrower pulse width than a coupled moderator, and so it will give us a better energy resolution. However, the peak neutron flux of the decoupled moderator has only a half of the coupled moderator. In order to decide the best choice of this type of near-backscattering instruments, we have reconsidered instrumental parameters including the type of moderators. We have performed Monte-Carlo neutron ray-tracing simulations, using McStas and have compared these results in various viewpoints such as intensities, resolutions, shape of resolution functions, scan ranges and so on.