Angular width of a narrow beam for X-ray linear attenuation coefficient measurements

The detection of scattered radiation can be a major source of systematic errors when measuring the X-ray linear attenuation coefficient, μμ. Angular distributions of scattered photons are studied for Z=1Z=1 to 20 at energies 6 keV to 100 MeV, using tabulated atomic form factors and incoherent scattering functions. A circularly symmetric pencil beam irradiation geometry is considered, and scatter acceptance angles, equal to the sum of the incident and exit beam divergence, are evaluated for systematic errors of 0.5–1.0% in measuring μμ. The analysis is extended to water, comparing predictions based upon the independent atomic model to values obtained from tabulated molecular form factors.