Conceptual design of a macromolecular neutron diffractometer (MaNDi) for the SNS

This paper describes the design criteria, calculations and simulations for a high-resolution macromolecular neutron diffractometer (MaNDi) for the Spallation Neutron Source (SNS). MaNDi is optimized to achieve 1.5 Å resolution from crystals of 0.1–1 mm³ with lattice repeats in the range of 150 Å. It was determined that locating MaNDi on a decoupled hydrogen moderator beamline with a curved guide will provide data of higher resolution and higher signal-to-noise than a coupled hydrogen moderator at the SNS. In addition, for an instrument with an initial flight path of 24 m at the 60 Hz source and a wavelength bandwidth of Δλ ≃ 2.7 Å, bandwidth selection disk choppers can shift the wavelength range higher or lower for different experiments. With a wavelength range of 1.5–4.2 Å and d_min = 2.0 Å, simulations predict experiment duration times of 1–7 d, which is expected to revolutionize neutron macromolecular crystallography (NMC) for applications in the fields of structural biology, enzymology and computational chemistry.