Development of a Dual-Particle Imaging System for Nonproliferation Applications.

Abstract

A rising concern in our society is preventing the proliferation of nuclear weapons and fissionable material. This prevention can be incorporated at multiple levels, from the use of nuclear safeguards in nuclear facilities to the detection of threat objects in the field. At any level, systems used for such tasks need to be specially designed for use with Special Nuclear Material (SNM) which is defined by the NRC as plutonium and uranium enriched in U-233 or U-235 isotopes. These radioactive materials have the particularity of emitting both fast neutrons and gamma rays; thus, systems able to detect both particles simultaneously are particularly desirable. In the field of nuclear nonproliferation and safeguards, detection systems capable of accurately imaging various sources of radiation can greatly simplify any monitoring or detection task. The localization of the radiation sources can allow users of the system to focus their efforts on the areas of interest, whether it be for radiation detection or radiation characterization. This thesis describes the development of a dual-particle imaging system at the University of Michigan to address these technical challenges. The imaging system relies on the use of organic liquid scintillators that can detect both fast neutrons and gamma rays, and inorganic NaI(Tl) scintillators that are not very sensitive to neutrons yet yield photoelectric absorptions from gamma rays. A prototype of the imaging system has been constructed and operated. The system will aid the remote monitoring of nuclear materials within facilities, and it has the scalability for standoff detection in the field. A software suite has been developed to analyze measured data in real time, in an effort to obtain a system as close to field-ready as possible. The system’s performance has been tested with various materials of interest, such as MOX and plutonium metal, measured at the PERLA facility of the Joint Research Center in Ispra, Italy. The robust and versatile imaging system is an attractive alternative to the current imaging systems.