A multiple angle detection system for coherently scattered X-ray signatures
Coherent scatter measurements have previously shown promise as a method for detection and identification of materials. However, the time required for measurements is rather long and the computer power required to analyse the data can be quite considerable. A multiple angle coherent scatter system has been designed and built to assess the feasibility of using this technique as an alternative to a single angle coherent scatter system. An application of detecting the presence of explosives within baggage to go on board aircraft was used to test the multiple angle system. A cadmium zinc telluride detector was found to be suitable to be used with the multiple angle system. A model of the system was used to determine the number of angles required and to determine the characteristics of the collimator that would be suitable with this detector. The objective of this work was to develop a simple method of analysing the data yielded from multiple angle coherent scatter system. This has been achieved by plotting the scatter signatures in the form of energy-angle diagrams and using these plots to determine the optimum energy windows to be used with each scatter angle. Samples of 4 mm of Semtex and 6 mm of SX2 were detected with 0% false alarm rate at 100% detection rate with a single energy window centred at a planar spacing of 3.3 Å. A detector array with collimation has been built to fit within the dimensions of an existing baggage scanner. This caused an increase in the scatter volume and hence the explosive sample constituted a smaller part of it. The results were that the false alarm rate was higher than for the initial system, at 37.5% It is concluded that the multiple angle detection of coherent scatter signatures is a promising method for the detection of explosives and that it could be used for several other applications in the future.