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Gamma-ray Imaging Methods

Description: In this document we discuss specific implementations for gamma-ray imaging instruments including the principle of operation and describe systems which have been built and demonstrated as well as systems currently under development. There are several fundamentally different technologies each with specific operational requirements and performance trade offs. We provide an overview of the different gamma-ray imaging techniques and briefly discuss challenges and limitations associated with each modality (in the appendix we give detailed descriptions of specific implementations for many of these technologies). In Section 3 we summarize the performance and operational aspects in tabular form as an aid for comparing technologies and mapping technologies to potential applications.
Date: October 5, 2006
Creator: Vetter, K; Mihailescu, L; Nelson, K; Valentine, J & Wright, D
Partner: UNT Libraries Government Documents Department

Gamma-ray imaging with coaxial HPGe detector

Description: We report on the first experimental demonstration of Compton imaging of gamma rays with a single coaxial high-purity germanium (HPGe) detector. This imaging capability is realized by two-dimensional segmentation of the outside contact in combination with digital pulse-shape analysis, which enables to image gamma rays in 4{pi} without employing a collimator. We are able to demonstrate the ability to image the 662keV gamma ray from a {sup 137}Cs source with preliminary event selection with an angular accuracy of 5 degree with an relative efficiency of 0.2%. In addition to the 4{pi} imaging capability, such a system is characterized by its excellent energy resolution and can be implemented in any size possible for Ge detectors to achieve high efficiency.
Date: April 12, 2005
Creator: Niedermayr, T; Vetter, K; Mihailescu, L; Schmid, G J; Beckedahl, D; Kammeraad, J et al.
Partner: UNT Libraries Government Documents Department

Methods for increasing the efficiency of Compton imagers

Description: A Compton scatter camera based on position sensitive, planar Ge and Si(Li) detectors with segmented electrodes is being developed at LLNL. This paper presents various methods that were developed to increase the position resolution of the detectors, the granularity and capability to reconstruct the scattering sequence of the gamma-ray within the detectors. All these methods help to increase the efficiency of the imager, by accepting more photons in the final image. The initial extent and diffusion of charge-carrier clouds inside the semiconductor detectors are found to affect profoundly the fraction of interactions that deposit charge in multiple adjacent electrodes. An accurate identification of these charge-shared interactions is a key factor in correctly reconstructing the position of interactions in the detector.
Date: November 15, 2005
Creator: Mihailescu, L; Vetter, K; Burks, M; Chivers, D; Cunningham, M; Gunter, D et al.
Partner: UNT Libraries Government Documents Department

Imaging Performance of the Si/Ge Hybrid Compton Imager

Description: The point spread function (PSF) of a fully-instrumented silicon/germanium Compton telescope has been measured as a function of energy and angle. Overall, the resolution ranged from 3{sup o} to 4{sup o} FWHM over most of the energy range and field of view. The various contributions to the resolution have been quantified. These contributions include the energy uncertainty and position uncertainty of the detector; source energy; Doppler broadening; and the 1/r broadening characteristic of Compton back-projection. Furthermore, a distortion of the PSF is observed for sources imaged off-axis from the detector. These contributions are discussed and compared to theory and simulations.
Date: November 10, 2005
Creator: Burks, M; Chivers, D; Cork, C; Cunningham, M; Fabris, L; Gunter, D et al.
Partner: UNT Libraries Government Documents Department

First-Generation Hybrid Compact Compton Imager

Description: At Lawrence Livermore National Laboratory, we are pursuing the development of a gamma-ray imaging system using the Compton effect. We have built our first generation hybrid Compton imaging system, and we have conducted initial calibration and image measurements using this system. In this paper, we present the details of the hybrid Compton imaging system and initial calibration and image measurements.
Date: November 7, 2005
Creator: Cunningham, M; Burks, M; Chivers, D; Cork, C; Fabris, L; Gunter, D et al.
Partner: UNT Libraries Government Documents Department


Description: Oak Ridge National Laboratory (ORNL) and Lawrence Livermore National Laboratory (LLNL) have jointly performed tests to demonstrate combined measurements with a three-dimensional (3D) design information verification (DIV) system and a gamma-ray imager for potential safeguard applications. The 3D DIV system was made available by the European Commission's Joint Research Center to ORNL under a collaborative project between the U.S. Department of Energy and the European Atomic Energy Community (EURATOM). The system is able to create 3D maps of rooms and objects and of identifying changes in positions and modifications with a precision on the order of millimeters. The gamma ray imaging system consists of a 4{pi} field-of-view Compton imaging system which has two fully operational DSSD (Double-Sided Segment Detector) High-Purity Germanium (HPGe) detectors developed at LLNL. The Compton imaging instrument not only provides imaging capabilities, but provides excellent energy resolution which enables the identification of radioisotopes and nuclear materials. Joint Research Center was responsible to merge gamma-ray images with the 3D range maps. The results of preliminary first measurements performed at LLNL demonstrate, for the first time, mapping of panoramic gamma-ray images into 3D range data.
Date: June 14, 2006
Creator: Mihailescu, L; Vetter, K; Ruhter, W; Chivers, D; Dreicer, M; Coates, C et al.
Partner: UNT Libraries Government Documents Department