High-sensitivity Compton imaging with position-sensitive Si and Ge detectors

Abstract

We report on the development of high-sensitivity and compact Compton imaging systems built of large and position-sensitive Si(Li) and HPGe detectors. The primary goal of this effort is to provide improved capabilities in the passive detection of nuclear materials for homeland security. Our detectors are implemented in double-sided strip configuration which -along with digital signal processing -provides energies and three-dimensional position information of individual gamma-ray interactions. Gamma-ray tracking algorithms are then determining the scattering sequence of the gamma ray which in turn allows us -employing the Compton scattering formula -to reconstruct a cone of possible incident angles and ultimately an image. This Compton imaging concept enables large-field-of-view gamma-ray imaging without the use of a heavy collimator or aperture. The intrinsically high energy resolution of the detectors used, the excellent position resolution we have demonstrated, both combined with the high efficiency of large-volume detectors is the basis for high Compton imaging sensitivity. These capabilities are being developed to identify and localize potential threat sources and to potentially increase the sensitivity in detecting weak sources out of the midst of natural, medical, or commercial sources. Gamma-ray imaging provides a new degree of freedom to distinguish between spatial and temporal background fluctuations and compact threat sources.

The effects of Doppler broadening and detector resolution on the performance of three‐stage Compton cameras

“…We based the size of the detectors used in our simulation on large detectors described in the literature. One similarly sized detector currently in use is the Compact Compton imager (CCI-1), a HPGe detector with dimensions 76 × 76 × 11 mm 3 , built and studied by Vetter et al, 23 who are also developing a 30-mm-thick detector. Another example is the University College of London HPGe CC built by ORTEC, which combines 152 4 × 4 × 4-mm 3 pixels for a total surface area of 2432 mm 2 and a depth of 0.4 mm.…”

“…27 Although this formula is more than 25 years old, it is still in agreement with current literature. For example, it predicts the 1.4 and 1.7-keV resolutions for 60 and 662-keV incident gamma reported by Vetter et al 23 and the 1.8 and 1.9-keV resolutions for 356 and 662-keV incident gamma reported by Alnaaimi et al 24 For CZT, we model the energy resolution FWHM using the formula developed by Du et al 28 δ…”

A Fieldable-Prototype, Large-Area, Gamma-Ray Imager for Orphan Source Search

“…This indicates that one does not yet have the sensitivity to truly image the ambient background. To achieve this level of performance requires more advanced instruments that have improved shielding and or take advantage of other imaging modalities such as Compton imaging [22], [23].…”

Silicon Photomultiplier-Based Compton Telescope for Safety and Security (SCoTSS)

“…Alternately, it would allow investigation of a scene without disturbing it, providing personnel safety from loose sources of radioactivity, and preserving evidence for eventual prosecution. Some earlier work in developing imagers for safety and security made use of solid-state devices such as high purity germanium [5]. For field operation, however, it would be best to avoid the use of instruments which require cryogenic cooling.…”