This standard specifies the operational and performance requirements for active interrogation systems for use in homeland security applications. These systems employ penetrating ionizing radiation (e.g., neutrons, high-energy x-rays, gamma-rays) to detect and identify hidden chemical, nuclear, and explosive agents by detection of stimulated secondary radiations or by nuclear resonance contrast, giving elemental and/or nuclidic identification of the composition of the substances-of-interest. These inspection systems may be designed for open inspection zones of various sizes or for various sizes of containers such as small packages, briefcases, suitcases, air cargo containers, passenger vehicles, two-axle trucks, intermodal cargo containers, semi-trailers/tractor rigs, or rail cars. The systems may be designed for operation in indoor, outdoor, or mobile facilities. At the time of this writing, there are only a few commercially available active interrogation systems, and most of these are still in a stage of rapid development. None are yet deployed on a very broad scale, either domestically or internationally. The requirements of this standard provide a set of minimally acceptable performance criteria for preliminary screening of candidate systems for further consideration. Prior to deployment on a broad scale, more detailed and realistic testing beyond the scope of this standard should be carried out, with some test specifications outside of the public domain. Detectable amounts of substances in this standard may correspond to quantities that are larger or smaller than those of significance in particular circumstances. Successful completion of the tests described in this standard should not be construed as certification of an ability to successfully detect and identify all chemical, nuclear, and explosive agents in all possible cargos, nor as a certification that false positive rates in actual stream-of-commerce applications will be no larger than in these tests. This standard does not consider radiographic imaging characteristics. However, if active interrogation features that provide chemical or nuclidic identification of substances are included in a system that is primarily intended for radiography, then the active interrogation features of the system may be tested and evaluated under this standard.