The analyzer in neutron protein crystallography

The use of a pyrolytic graphite analyzer is shown to contribute to the cleanliness of a neutron protein crystallographic study. If neutrons of approximately 1.5-A wavelength are used, higher orders are reduced by nearly an order of magnitude, and background (arising largely from incoherent inelastic neutron-proton scattering) is reduced by nearly a factor of five. These advantages are gained at the expense of approximately 50% of measured integrated intensity and a distortion of integrated intensity with scattering angle. Because background scatter is generally large compared with peak reflectivity of a protein, the large background reduction by the analyzer more than compensates for reduced peak intensity to improve the statistics of most peak reflectivity measurements. The luminance function distortion of intensity data is not large, produces a slight smearing of atomic scattering density, and can be calculated and adjusted for in the data.