The effective collimation ratio, L/D, of neutron radiography beams is measured using an empirical technique defined in ASTM E803-20. The method is based on examining a neutron radiography image and is unaffected by measurements and calculations based on the collimation system's physical dimensions. The values expressed in SI units should be considered standard.
Scope:
The standard test method L/D Ratio of Neutron Radiography Beams ASTM E803-20 is used to determine and periodically measure the actual collimation ratio. By using ASTM E803-20, neutron beamlines with cold or heat neutron spectrums are tested. For ASTM E803-20, neutron pictures can be created on radiographic film using a conversion screen described in Guide E748 or a CR screen with a neutron converter.
Procedure:
In the ASTM E803-20 test, the NU (no umbra) approach is used to determine the neutron beam L/D ratio by radiographing the NU device with the neutron beam to be measured and then evaluating the resulting image using one of three methods. The three methods are all dependent on determining the point at which the umbral shadow width reaches zero.
Specimen size
In ASTM E803-20, the NU device is used that consists of cadmium rods that are placed in V-grooves on the surface of an aluminum channel section that has been precisely cut.
Result
In ASTM E803-20, the specific image capture technique employed shall be reported, including the digitization process if film images are digitized, the calculation method(s), and the L/D ratio(s).
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