Measurement techniques to combat nuclear terrorism

To combat illicit use of nuclear and radioactive material and to take preventive action reliable measurement techniques are imperative for early detection of this material. Nuclear safeguards are an important tool to impede the illicit use of fissionable material. But only nuclear material is controlled by safeguards, radioisotope sources are not covered by the safeguards regime in general. Whereas in most western countries comprehensive regulations for the control of radioactive materials exist a lot of other countries have inadequate control and monitoring programs to prevent or even detect the theft of these materials. While radiation accidents caused by orphan sources may give an idea on the extent of such a risk, the injury caused by a well planed terrorist attack with radioactive or nuclear material may be even worse. Since the threat environment is very unpredictable mobile measuring systems are essential to detect and respond to malicious acts involving radioactive or nuclear material. For the detection and identification of radioactive and nuclear material Fraunhofer INT has built up a mobile measuring system integrated into a transportable container. A power generator on a trailer makes the system independent of local resources of electric power. This container as well as the power generator can be transported by land, air or sea. The system is equipped with various types of detectors for neutron and gamma radiation, some of the detectors are similar to those used in safeguards. The type of radiation and its activity level can be determined. In case of neutron emitting material it is possible to distinguish fissionable material from random neutron sources by means of coincidence counting. This system is completed by a measurement car, which is equipped with high efficient neutron detectors and a background subtracting gamma measurement system. With this system hidden radioactive material can also be revealed by a covered search. In case of a radiological dispersal device or an improvised nuclear device the danger zone may extend to several hundred meters. In this case the detectors and electronics are moved with a remote controlled manipulator vehicle near the suspicious object. The measured data are transferred via radio transmission to the container placed in a safe distance for evaluation and risk assessment. Depending on availability of telecommunication infrastructure, the measurement results can be communicated by telephone line, mobile phone or satellite. Based on the results the next action steps are decided by law enforcement authorities. The capabilities of these mobile detection systems have been demonstrated in field exercises. Details of on-site identification measurements and results will be presented