Matrix Characterization in Threat Material Detection Processes

Matrix characterization in the threat material detection is of utmost importance, it generates the background against which the threat material signal has to be identified. Threat materials (explosive, chemical warfare, ...) are usually contained within small volume inside large volumes of variable matrices. We have studied the influence of matrix materials on the capability of neutron systems to identify hidden threat material. Three specific scenarios are considered in some details: case 1--contraband material in the sea containers, case 2 - explosives in soil (landmines), case 3 - explosives and chemical warfare on the sea bottom. Effects of container cargo material on tagged neutron system are seen in the increase of gamma background and the decrease of neutron beam intensity. Detection of landmines is more complex because of variable soil properties. We have studied in detail space and time variations of soil elemental compositions and in particular hydrogen content (humidity). Of special interest are ammunitions and chemical warfare on the sea bottom, damping sites and leftovers from previous conflicts (WW-I, WW-II and local). In this case sea sediment is background source and its role is similar to the role of the soil in the landmine detection. In addition to geochemical cycling of chemical elements in semi-enclosed sea, like the Adriatic Sea, one has to consider also anthropogenic influence, especially when studying small scale variations in concentration levels. Some preliminary experimental results obtained with tagged neutron sensor inside an underwater vehicle are presented as well as data on sediment characterization by X-Ray Fluorescence.