Preventing terrorists acts by early detection of illicit RN material on-site

To prevent the misuse of nuclear or radioactive material for malicious acts sensitive and reliable detection systems are mandatory. In addition to fixed monitors installed at border crossings, at the gateways of nuclear and industrial facilities or at the entrance of a military camp mobile handheld systems are needed to detect the dangerous material on-site as early as possible with high reliability excluding false alarms caused by natural radioactivity (like in potash fertilizer) or by patients which have undergone a nuclear medical therapy respectively examination. We investigated highly sensitive passive detection systems for gamma and neutron radiation. In a static situation an overview of the situation is gained by scanning of buildings or objects with a gamma camera. Here gamma intensity is converted into colors and then superimposed on the optical picture in order to get a visual overview. Terrorist attacks using nuclear material may have far reaching consequences compared to an attack with pure Gamma-sources. Nuclear material can be detected by neutron emissions from spontaneous fission as well as by the neutrons produced by (alpha, n) reactions in surrounding material. Therefore we operate a sensitive neutron detection system, fitted into a suitcase. With a special analysis procedure it is possible to categorize the substance in fissionable and non-fissionable material. In addition, the system can discover the existence of shielding material located around the source material. The presence of shielding material gives important information for the evaluation of the possible risk and appropriate protection measures