Evaluation of the Resolvable Capacity of Bragg Reflections for a New Diffractometer at J-PARC/MLF Designed for Protein Crystals With Large Unit Cells

We aim to build a high-resolution neutron time-of-flight diffractometer for biomacromolecules at the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC) that allows the collection of neutron diffraction data from crystals with unit cells of ≈250 A. Considering both the flux and pulse width necessary to realize data collection covering a minimum d-spacing of 2.0 A and with a unit cell constant of ≈250 A, we chose a decoupled moderator (DM) as the appropriate source for this high-resolution diffractometer. We considered a simple instrumentation model that includes a moderator, neutron guide, sample size, and neutron detector; we then investigated its spot separation performance and estimated the instrumental parameters for the design of a new diffractometer for protein crystals with large unit cells at J-PARC/MLF.