Semiconductor beta and gamma detectors

The principles of semiconductor nuclear particle detectors and their applications are reviewed, and recent progress is reported, with particular attention to detection of beta and gamma radiations. By a lithium ion drift process, p-i-n structures with 5-mm (millimeter) depletion depth can now be fabricated routinely in silicon. Such counters have about a 5% efficiency for the detection of gamma photons; when cooled they sometimes show energy resolutions of under 10 kev (kiloelectron-volts). Recent results using germanium, which has a much higher photoelectric absorption cross section, show the photoelectric peak is well above the Compton background for the 660-kev gamma radiation from Cs¹³⁷, with a line width less than 7 kev for the 120-kev gamma from Co⁵⁷. The possibilities of other materials for large volume particle detectors are discussed.