ASTM E2861-16 test method covers the design, materials, manufacture, and use of a divergence and alignment indicator (DAI) for determining the alignment of the imaging plane relative to the beam centerline and measuring the affective divergence of a thermal neutron beam used for neutron imaging. The values expressed in SI units should be considered the standard.
Scope:
The standard test method ASTM E2861-16 is used to test thermal neutron imaging. To obtain an image, typically, a high flux reactor source with a well-defined collimation mechanism is used by classical neutron radiography. In neutron computed tomography, knowing the beam’s centerline and degree of beam divergence with some precision is critical, especially if the beam does not closely resemble a parallel beam.
Procedure:
In ASTM E2861-16, for a thermal neutron beam, the alignment of the imaging plane with the beam centerline and the beam divergence is determined. Then, circular symmetry is used to simplify production. The DAI is positioned in the physical center of the beam with the five stand-off posts against the film cassette or radioscopic imaging device. The DAI is perpendicular to the beam radius chosen. Finally, the cadmium wire is used to determine the degree of misalignment.
Specimen size
The DAI is made of aluminum plate and rods, with cadmium wires for contrast.
Data:
α = )
where:
α = the divergence angle
Result
The result shows the misalignment in the x and y directions of the calculated divergence angle at each axial and radial location.
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