A mechanically cooled, highly portable, HPGe-based, coded-aperture gamma-ray imager.

Coded-aperture gamma-ray imaging is a mature technology that is capable of providing accurate and quantitative images of nuclear materials. Although it is potentially of high value to the safe-guards and arms-control communities, it has yet to be fully embraced by those communities. This can be attributed to the limited choice, high cost, and low efficiency of commercial instruments, and the general unsuitability for field work of instruments made by research organizations. In this paper we present the results of a project that mates the coded-aperture-imaging approach with the latest in commercially available, position-sensitive, high purity germanium (HPGe) detectors. The instrument replaces a laboratory prototype that was suitable only for demonstrations. The original instrument, and the cart on which it is mounted to provide mobility and pointing capabilities, has a foot-print of ∼ 2/3 m by 2 m, weighs ∼100 Kg, and requires cryogen refills every few days. In contrast, the new instrument is tripod-mounted, weighs ∼30 Kg, operates with a laptop computer, and is me-chanically cooled. The instrument is being used in a program that is exploring the use of combined radiation and laser-scanner imaging. The former provides information on the presence, location, and type of nuclear materials; while the latter provides design verification information. To align the gamma-ray images with the laser-scanner data, the HPGe imager is fitted and aligned to a visible-light stereo imaging unit. This unit generates a locus of three-dimensional (3D) points that can be matched to the precise laser-scanner data. With this approach, the two instruments can be used completely independently at a facility, and yet, the data can be accurately overlaid based on the very structures that are being measured. [ABSTRACT FROM AUTHOR]