Terrorist use of radioactive nuclear materials is a serious threat for mass destruction or disruption of civil and military activities. Most worrisome is the use of nuclear devices to cause massive casualties to people and damage to structures. Fortunately, the procurement of adequate material and the engineering design, construction, and transportation and triggering of a nuclear weapon are all difficult problems for terrorist organizations. More likely is a device that combines radioactive materials with conventional explosives to make a radiological dispersion device, commonly called a...