| definition |
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Germanium Semiconductor Detector (GSD) are semiconductor diodes
having a P-I-N structure in which the Intrinsic (I) region is
sensitive to ionizing radiation, particularly X-rays and gamma
rays. Under reverse bias, an electric field extends across the
intrinsic or depleted region. When photons interact with the
material within the depleted volume of a detector, charge
carriers (holes and electrons) are produced and are swept by the
electric field to the P and N electrodes. This charge, which is
in proportion to the energy deposited in the detector by the
incoming photon, is converted into a voltage pulse by an
integral charge sensitive preamplifier.
Because germanium has a relatively low band gap, these detectors
must be cooled in order to reduce the thermal generation of
charge carriers (thus reverse leakage current) to an acceptable
level. Otherwise, leakage current induced noise destroys the
energy resolution of the detector. Liquid nitrogen, which has a
temperature of 77?K is the common cooling medium for such
detectors. The detector is mounted in a vacuum chamber which is
attached to or inserted into an LN2 dewar or an electrically
powered cooler. The sensitive detector surfaces are thus
protected from moisture and condensable contaminants.
[Source: CANBERRA "http://www.canberra.com"]
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