Development of a Neutron Scatter Camera for Fission Neutrons

Special nuclear material (SNM) emits high energy radiation during active and passive interrogation. This radiation can be imaged thus allowing visualization of shielded and/or smuggled SNM. Although gamma-ray imaging is appropriate for many cases, neutrons are much more penetrating through hi-Z materials, and are thus preferred in certain scenarios (e.g. weapons grade Pu or HEU smuggled inside a lead pig several inches thick). Techniques for thermal neutron imaging have already been developed, but these approaches only image the moderating material, not the true SNM source. Traditional neutron detectors such as He3 tubes and scintillators simply count neutrons. We are developing an instrument that will directly image the fast fission neutrons from an SNM source using a neutron scatter camera. This technique has been shown to be 10 times more sensitive for solar neutrons over traditional neutron counting techniques. In addition to being a 4pi neutron imager, this instrument will also be an excellent neutron spectrometer, and will be able to differentiate between different types of neutron sources (e.g. fission, gamma-n, cosmic ray, and dd or dt fusion). Our instrument will be able to pinpoint the source location. We will present results from a prototype detector and discuss key parameters that determine detector performance.