Gamma-ray imaging with position-sensitive HPGe detectors

Abstract

Due to advances in manufacturing large and highly segmented HPGe detectors along with the availability of fast and high precision digital electronics it is now possible to build efficient and high-resolution Compton cameras. Two-dimensionally segmented semi-conductor detectors along with pulse-shape analysis allow to obtain three-dimensional positions and energies of individual gamma-ray interactions. By employing gamma-ray tracking procedures it is possible to determine the scattering sequence in the detector and ultimately to deduce the incident direction of gamma rays without the use of a attenuating collimator. These advanced gamma-ray tracking based Compton cameras are able not only to image gamma-ray sources with higher sensitivity than collimator-based systems but can increase the sensitivity in finding gamma-ray sources over non-imaging detectors, particularly in complex radiation fields. We have implemented a Compton camera built of a single doubule-sided strip HPGe detector with a strip pitch size of 2mm. A three-dimensional position resolution of 0.5mm at 122keV by using simple pulse-shape analysis is achieved. We have implemented image reconstruction procedures for search scenarios, which are of interest for national security applications. In addition, we have developed reconstruction procedures to optimize image quality which potentially finds applications in other areas as well.

Benefits of Position-Sensitive Detectors for Radioactive Source Detection

“…A common assumption in the field of security imaging is that sources of radiation are small, so they appear point-like to a detector [1]. There are many gamma-ray detection modalities including stationary radiation portal monitors [1], coded aperture imaging systems [2], arrays of scintillating detectors [3], and position-sensitive Compton detectors [4], [5]. Some detection algorithms are specific to certain modalities, such as using images reconstructed from a coded aperture system to detect a point-source [2].…”

Development of multielemental imaging on semiconductor Compton telescope

“…Moreover, a higher spatial resolution would be desired to observe more fine structure. These demands would be met if the γ-ray tracking technique and pulseshape analysis are implemented, which have been recently developed [23]. With these techniques implemented, the efficiency and the intrinsic characteristics are improved, thereby shortening the measurement time and improving the spatial resolution.…”

The Feasibility of Cask "Fingerprinting" as a Spent-Fuel, Dry-Storage Cask Safeguards Technique

“…The increased information obtained about each gamma-ray (a narrow ring, rather than 1/2 to 1/3 the field of view, as in a coded-aperture imager) means that signal to noise is improved. A number of groups are actively working on this technology, [16][17][18] but it will still be at least five years before practical instruments can be available.…”