Developing Low Cost Neutron Systems for the Detection of Explosives and Drugs

Detection systems for threat materials using neutrons exploit the capabilities of this radiation to reach inaccessible regions in material arrays and convey composition information through subsequent transmission and/or scattering processes. In this research we contrast the performance of expensive DEXA (dual energy x-ray absorption) and NEUGAT (dual beam fast neutron and gamma ray transmission) scanners with a novel low cost system concept that effectively utilises two beams and has useful performance features. An objective in threat material detection systems is to have sufficient sensitivity to distinguish threat materials from other materials. Potential users of neutron-based commercial threat material detection systems may in some instances be deterred by the high cost and the high technical know-how required in using them. In this ‘high-tech’ age, the potential benefits of basic counting systems using simple filters in detecting threat materials is often overlooked.. While demand for sensitive systems that combine all leading edge technologies is inevitable by richer companies/countries, lower cost systems with at least a modest sensitivity is a priority especially if operator experience can assist in limiting any shortcomings. Such lower cost systems may take advantage of ‘near-spent’ lower-activity radioisotope-based neutron sources (e.g. less than 0.2 μg of 252Cf) withdrawn from industrial use. Use of transmission geometry can keep count times short and counting precision high through use of large bulk combinations of basic plastic scintillators that are easy to fabricate and assemble as robust units. Use of PC based discriminators and counting boards (for example) provides reliable and stable electronic performance. In this work we investigate use of appropriate filters (e.g. lead) placed in front of large plastic scintillators, to mimic composition detection capabilities of the more expensive systems. Polyethylene, acrylic, aluminium, water and sand are used as test materials having a range of hydrogen content and effective atomic number values similar to threat materials.