1. A secondary collimator, comprising: a body formed of a high density material; and a continuous spiral slit aperture formed in the body, wherein the continuous spiral slit aperture is oriented with a spirally increasing azimuth angle to enable multiple scatter beams to simultaneously pass through the continuous spiral slit aperture at different scatter angles for extending a range of momenta for which x-ray diffraction (XRD) intensities are measured for a predetermined range of photon intensities.