gamma-ray solid-state detectors
gamma-ray solid-state detectorsSemiconductor detectors designed to give high spectral resolution in the spectral domain in which the characteristic nuclear decay lines are emitted. Electron-hole pairs are created in a solid-state device along the path of the secondary electrons derived from γ-ray interactions, much as ion pairs are created in a gas-filled detector (see proportional counter). Applying an electric field to the detector enables the electron-hole pairs to be collected and thus provides the basic electrical signal from the device. Semiconductor detectors may be rendered position-sensitive, and hence adapted to provide imaging systems, by appropriate geometric design of the electrode contacts.
A variety of semiconductors are suitable for such detector systems. Silicon, either in the form of silicon diodes or lithium-drifted silicon, provides high-quality detectors for operation at hard X-ray/γ-ray energies (< 50 keV). High-purity germanium (HPGe), either in planar or coaxial form, currently provides the best-available spectral resolution for γ-rays (up to ˜10 MeV); germanium devices, however, must be cooled to ˜70 K for effective operation. Two semiconductors, mercuric iodide (HgI2) and cadmium telluride (CdTe), currently show great promise for room-temperature operation, and hence in telescopes would not need cooling; difficult to produce with sufficient purity, they are best-employed as thin detector systems in hard X-ray/γ-ray telescopes that operate typically in the range 5–300 keV.