【国外标准】 Standard Test Method for Measurement of Beam Divergence and Alignment in Neutron Radiologic Beams

5.1 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.1.1 This test method covers the design, materials, manufacture, and use of a divergence and alignment indicator (DAI) for measuring the effective divergence of a thermal neutron beam used for neutron imaging as well as determining the alignment of the imaging plane relative (usually normal) to the centerline of the beam. This test method is applicable to thermal neutron imaging.1.2 The values stated in SI units are to be regarded as the standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.