4.1 One of the factors affecting the quality of a radiographic image is geometric unsharpness. The degree of geometric unsharpness is dependent upon the size of the source, the distance between the source and the object to be radiographed, and the distance between the object to be radiographed and the film or digital detector. This test method allows the user to determine the size of the source and to use this result to establish source to object and object to film or detector distances appropriate for maintaining the desired degree of geometric unsharpness.

Note 1: The European standard CEN EN 12579 describes a simplified procedure for measurement of source sizes of Ir-192, Co-60, and Se-75. The resulting source size of Ir-192 is comparable to the results obtained by this test method.

1.1 This test method covers the determination of the size of Iridium-192, Cobalt-60, and Selenium-75 radiographic sources. The determination is based upon measurement of the image of the source in a projection radiograph of the source assembly and comparison to the measurement of the image of a reference sample in the same radiograph or the source guide tube.

1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.

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.