University of Michigan -- 1994-5 performance review of D&D activities. Annual report, June 1, 1994--May 31, 1995

In accordance with work proposed to the ORNL D & D Program, UM navigation group has conducted research in two areas: (1) Theoretical and experimental work for the improvement of dead-reckoning accuracy in mobile robots and (2) a comprehensive literature survey on positioning methods for mobile robots. The radiation imaging group has conducted research in: (1) assessing the existing requirements for gamma ray imagers, (2) hot testing of existing gamma ray imagers, and (3) design and testing of a prototype rotating aperture camera for improved signal/noise ratios and sensitivity

Development of gamma ray imaging cameras

In January 1990, the Department of Energy initiated this project with the objective to develop the technology for general purpose, portable gamma ray imaging cameras useful to the nuclear industry. The ultimate goal of this R D initiative is to develop the analog to the color television camera where the camera would respond to gamma rays instead of visible photons. The two-dimensional real-time image would be displayed would indicate the geometric location of the radiation relative to the camera's orientation, while the brightness and color'' would indicate the intensity and energy of the radiation (and hence identify the emitting isotope). There is a strong motivation for developing such a device for applications within the nuclear industry, for both high- and low-level waste repositories, for environmental restoration problems, and for space and fusion applications. At present, there are no general purpose radiation cameras capable of producing spectral images for such practical applications. At the time of this writing, work on this project has been underway for almost 18 months. Substantial progress has been made in the project's two primary areas: mechanically-collimated (MCC) and electronically-collimated camera (ECC) designs. We present developments covering the mechanically-collimated design, and then discuss the efforts on the electronically-collimated camera. The renewal proposal addresses the continuing R D efforts for the third year effort. 8 refs

A source reconstruction method for multiple scatter Compton cameras

A new method for finding the direction of gamma rays incident on a multiple scatter Compton camera has been proposed. The method uses the polarization dependence of double Compton scattering to reduce the azimuthal ambiguity normally associated with interpreting Compton scattering events. The CYLTRAN photon Monte Carlo code was modified to include the polarization effects of gamma rays undergoing Compton scattering in the 150-1000-keV energy range and used to test the method. Results for 150-keV gamma rays incident upon a multiple Compton scatter imaging camera are presented.<

Application of expert systems to heat exchanger control at the 100-megawatt high-flux isotope reactor

The High-Flux Isotope Reactor (HFIR) is a 100-MW pressurized water reactor at the Oak Ridge National Laboratory. It is used to produce isotopes and as a source of high neutron flux for research. Three heat exchangers are used to remove heat from the reactor to the cooling towers. A fourth heat exchanger is available as a spare in case one of the operating heat exchangers malfunctions. It is desirable to maintain the reactor at full power while replacing the failed heat exchanger with the spare. The existing procedures used by the operators form the initial knowledge base for design of an expert system to perform the switchover. To verify performance of the expert system, a dynamic simulation of the system was developed in the MACLISP programming language. 2 refs., 3 figs

A ring Compton scatter camera for imaging medium energy gamma rays

The characteristics of a new ring Compton scatter camera are described. This camera is designed to image medium energy (0.5 to 3 MeV) gamma-ray fields. It consists of two positron sensitive detector arrays, i.e. a 4*4 planar array of high purity germanium (HPGe) crystals and a ring array of up to 64 NaI(Tl) crystals. Past evaluations of Compton cameras have employed a planar second detector, which is subjected to a large flux of gamma rays that either pass directly through or undergo small angle scatter in the first detector. A ring array significantly reduces direct and small angle scattered events in the second detector. An analytical model for ring camera systems is developed to predict angular resolution and efficiency, and is benchmarked against measurements made with a prototype system consisting of the 4*4 HPGe array and an eight-element ring. Predictions are made for a system with 64 crystals in the second detector ring.<