Standard Test Method for Measurement of Beam Divergence and Alignment in Neutron Radiologic Beams

As discussed in Practice E748, traditional neutron radiography typically employs a high flux reactor source with a well defined collimation system to produce an image on film. The alignment of the imaging plane and the divergence angle are generally well defined and a small degree of misalignment or uncertainty in divergence angle makes little difference in the final image. These systems are well characterized by their physical dimension, the L/D ratio, and image quality indicators (Beam Purity Indicator and Sensitivity Indicator) described in Test Method E545. Neutron computed tomography is an example where it is important to know with some precision both the beam’s centerline and the degree of beam divergence, especially if the beam does not closely approximate a parallel beam. Portable or movable neutron imaging systems often utilize shorter collimation systems, a less precise alignment and poor symmetry in divergence angles, which may affect image analysis. In these example cases, direct measurement of the alignment and the divergence angles is desirable as calculation from system geometry would be less straightforward and accurate. Fabrication of the device is an extension of the Test Method E803 L/D device, providing different information through a similar approach.