Year
2011
Abstract
Future strategic arms control treaties may require verification of the number of warheads installed upon a missile. Inspections supporting such verification will likely be subject to many constraints. One of these is that a measurement should not reveal classified warhead information. In addition, a highly desirable feature would be the ability to determine, within a single measurement, the warhead count of a missile at several meters standoff. Fast neutron imaging appears to be especially attractive for this arms-control application. Unlike gamma rays, fast neutrons emitted by a warhead have little potential to reveal detailed information about the composition of the source, and they can easily penetrate the warhead and surrounding material. Here we describe a technology that could provide very high intrinsic fast neutron imaging resolution, possibly allowing warhead counting measurements with a minimum of postprocessing – a desirable feature for confidence building and transparency. Time Projection Chambers (TPCs), which have been widely used in particle and nuclear physics research for several decades, provide a convenient means of measuring the full 3D trajectory, specific ionization (i.e particle ID) and energy of charged particles. For this application, observation of two recoil protons from a double fast neutron scatter on protons in hydrogen or methane gas provides a complete kinematic constraint upon the direction and energy of the incoming neutron. Intrinsic angular resolution of few degrees can be achieved by this technique, prior to any mathematical inversion or maximum likelihood imaging technique. This double scatter imaging mode has been demonstrated using a laboratory prototype device, despite the fact that it was entirely un-optimized for this application. We will describe these results, and present a device design well suited to warhead counting for treaty verification applications.