Wedges Used for Film Cassette Protection.
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
Pagination or Media Count:
High voltage flash x-ray systems are frequently used for observing explosive events. During such tests the x-ray screen and film must be protected from the blast from the charge, but the areal density of the protection must be small enough so that the x-rays are not blocked. In outdoor ranges this problem is minimized, but not eliminated, by letting the cassettes move in response to the blast. In enclosed chambers the problem is more severe because the motion of the cassettes must be restricted. Tests in our blast chambers are usually performed with the object about 2 - 4m from the x-ray tubes and about 0.6m from the cassette which holds the screen and film. The standard x-ray cassettes. consist of layers of aluminum, felt, foam, and a steel backing. They are typically 450mm by 530 mm in area. Based on the Hewlett Packard X-ray Manual, our 300kV flash x-rays will penetrate the equivalent of 50mm of aluminum at a distance of 3m. This means one can safely use 25 mm of aluminum on the front of the cassette and still have some ability to penetrate the test charge, Experience indicates that this is adequate to protect the cassette for explosive charges of up to 0.5 kg, but it is inadequate for larger charges. This report discusses the use of hollow wooden cones or wedges on the front of the cassette. The technique appears to offer excellent protection with a minimum of areal density.