Neutron diffractometer for protein crystallography covering large-unit-cell at J-PARC

Kurihara, Kazuo; Tomoyori, Katsuaki; Tamada, Taro

Many of membrane proteins and protein complexes have larger molecular weight and then unit cells of their crystals have larger volume. Therefore, our group had designed the diffractometer which is able to cover such a crystal with large unit cell volume (target lattice length: 250 ). This proposal was accepted by Neutron Instrument Program Review Committee of J-PARC in September 2012. Larger unit cell volume causes a problem to separate spots closer to each other in spatial and time distribution in diffraction images. Therefore, our proposed diffractometer adopted longer camera distance (800 mm) and decoupled moderator as neutron source which has shorter pulse width. The neutron guide tube was designed to use limited surface of the decoupled moderator with high luminescence (40 mm high 60 mm wide) whose luminosity is about 1.3 times as high as that of average of the whole surface in the wavelength range from 2.9 to 9.1 . Ellipsoidal and curved shape were introduced in the vertical and the horizontal design of the guide design, respectively, which provide maximum beam divergence of 0.8 in vertical and 0.6 in horizontal, respectively, at the sample position. According to ray-tracing simulation by McStas code, neutron flux at the sample position is estimated to be 510/cm/s in the wavelength range of 1.5 - 5.6 (first frame).