The Ibaraki prefecture materials design diffractometer for J-PARC; Designing neutron guide

Harjo, S.   ; Kamiyama, Takashi*; Torii, Shuki; Ishigaki, Toru; Yonemura, Masao*

Ibaraki Prefecture Materials Design Diffractometer of J-PARC is a time-of-flight neutron powder diffractometer with the resolution as good as / = 0.16 % (almost constant value) for (L1 of 26.5 m). Since this diffractometer has many detectors covering wide 2 range, measurements with wide range, , i.e., PDF analysis and small angle scattering can also be performed. Designing of neutron guide is therefore very important to enhance the performances mentioned above without sacrificing beam intensity. Non-parallel guides including elliptical ones have been compared with a linear-straight guide using the McStas simulation. The elliptical guide having the exit focal points away behind the sample position is available to increase the neutron flux at the sample but give a slight lowering of the instrumental resolution. This elliptical guide gives also Garland peaks at short wavelengths that may give large ambiguities in powder diffraction measurements. Therefore, the linear-straight guide is considered as the best choice for this instrument to keep a good resolution and also a relatively high flux.