W0170

Design of a High Resolution Neutron Macromolecular Crystallography Diffractometer at the SNS. P. Thiyagarajan¹, Arthur J. Schultz¹, Christine Rehm² and Jason P. Hodges², ¹Intense Pulsed Neutron Source and ²Spallation Neutron Source, Argonne National Laboratory, 9700 South Cass Ave, Argonne, IL 60439, USA.

A high resolution Neutron Macromolecular Crystallography Diffractometer (NMCD) at the Spallation Neutron Source (SNS) has been designed for fast and efficient measurements of Bragg intensities from macromolecular single crystals. The goal of the NMCD is to be able to collect a set of Bragg data with a resolution of 1.5 Å on a macromolecular crystal with a lattice constant of 150 Å (Δd/d = 1%). NMCD will simultaneously use a wide neutron band width (1.85 Å <_ λ < 4.5 Å) sorted by time-of-flight and an array of high spatial resolution position-sensitive area detectors. The collected neutron diffraction data will provide direct observation of hydrogen atoms in both waters of hydration and within the macromolecule. Our design calculations show that the decoupled liquid hydrogen moderator at the SNS is the appropriate for NMCD as it provides a high flux of cold neutrons with an optimal pulse width. Monte Carlo simulations show that recently developed high index supermirror neutron guides can achieve flux gains as high as ×10 at the sample position. Furthermore, the use of Soller collimators offers flexibility to match the flux, angular divergence and consequently instrument resolution to the experiment requirements. The expected performance of NMCD will be ~70 times that of present world-class reactor based instruments such as BIX3 at JAERI.

This work carried out at IPNS at Argonne National Laboratory was funded by the Office of BES, US DOE under contract # W-31-109-ENG-38 and a grant from ORAU to the Structural Biology Task Force for this design project.