gamma-ray solid-state detectors
gamma-ray solid-state detectors
Semiconductor 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.