Because of intelligence assessments of the likelihood that terrorists will attempt to attack targets in the United States with a radiological bomb, efforts to erect defenses to detect radiation-emitting weapons entering the United States are now a top priority. With partial funding from the Department of Homeland Security and the National Institute of Standards and Technology's (NIST's) Office of Law Enforcement Standards, NIST researchers are investigating a wide variety of detection devices, ranging from 3-meter-high portal towers that can scan truck trailers as they move through checkpoints, to small monitors that act as personal dosimeters. The new standards being developed will ensure that the devices work as intended under the new conditions of homeland security tasks. Because the smuggling of materials or weapons in shipping containers is a clear threat to the United States, NIST is developing a cargo-container inspection test bed to provide a means for calibrating detectors used for radioactivity measurements in the field. Because of increased concerns about a terrorist attack with a "dirty" bomb, NIST has begun new research in gamma-ray measurements. The speed with which these devices can be deployed is crucial, since there is evidence that terrorists are racing to construct radiological weapons and means of delivering them before the United States can create and/or fortify the necessary defenses.