Detection of Gammas with Ge Detectors

As mentioned in Sec. 7.5.5, the Ge(Li) detectors have been replaced by Ge detectors, which are devices that use hyper pure germanium (impurity concentration 10 atoms/m or less). The main advantage of Ge over Ge(Li) detectors is that the former should be kept at low temperatures only when in use the latter must be kept cool at all times. 

The vacuum chamber that contains the detector is made of stainless steel. The chamber protects the detector from dirt and, by being evacuated, prevents condensation of vapor on the detector surface or electrical discharge when high voltage is applied to the detector. A metal envelope, with a very thin window at its end for the passage of the incident photons, surrounds the detector. The window is made of beryllium, aluminum, or a carbon composite fiber. Transmission characteristics of several window thicknesses are shown in Fig. 12.23. Most commercial cryostats include the preamplifier as a standard component. 

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