The present invention relates generally to a method and apparatus for the detection of radioactive material and, more particularly, to a method and apparatus for detecting the presence of radioactive material within a vessel or container during shipment from one location to another. 
There is a growing concern that terrorists or others may at some time in the near future attempt to import into the United States or some other country radioactive or nuclear material which may then be used for the construction of a nuclear weapon for carrying out terrorist objectives.  One way of shipping such radioactive or nuclear material is to hide the material among or within seemingly innocuous cargo.  For example, such nuclear material could be placed within a standard, sealed cargo container of the type typically employed for shipping cargo by sea, rail, air or by truck.  The nuclear material could be positioned within such a sealed cargo container along with other innocuous goods with the container being positioned, for example, within the hold of a large container ship which may be transporting a thousand or more such containers from one location to another.  Typically, existing cargo inspection systems are employed either at the port of debarkation or the port of entry for such container ships.  Because of the large number of containers which are typically transported by a single large container ship, it is difficult, if not impossible, using the presently available inspection equipment and personnel to thoroughly check each and every container for the presence of any type of contraband, including radioactive or nuclear material.  To beef up the inspection equipment and personnel at ports of entry to facilitate a more thorough or detailed inspection of each container is not practical because of the time involved in inspecting each such container and the unacceptable delays in the transport of the containers, as well as potential huge back ups in the loading and unloading of the container ships. 
The present invention overcomes the problems associated with the existing container inspection systems by providing a method and apparatus for the detection of radioactive or nuclear material within a sealed container while the container is in transit from one location to another.  In this manner, it is possible to identify potential threats while in transit to permit appropriate action to be taken long before the radioactive or nuclear material enters the territorial limits of a country.