High‐resolution imaging gamma‐ray spectroscopy with externally segmented germanium detectors

Externally segmented germanium detectors promise a breakthrough in gamma‐ray imaging capabilities while retaining the superb energy resolution of germanium spectrometers. An angular resolution of 0.2° becomes practical by combining position‐sensitive germanium detectors having a segment thickness of a few millimeters with a one‐dimensional coded aperture located about a meter from the detectors. Correspondingly higher angular resolutions are possible with larger separations between the detectors and the coded aperture. Two‐dimensional images can be obtained by rotating the instrument. Although the basic concept is similar to optical or x‐ray coded‐aperture imaging techniques, several complicating effects arise because of the penetrating nature of gamma rays. The complications include partial transmission through the coded aperture elements, Compton scattering in the germanium detectors, and high background count rates. Extensive electron–photon Monte Carlo modeling of a realistic detector/coded–aperture/c...