= Germanium detector
A \b[germanium detector] is a <semiconductor detector> whose active material is <germanium>. Radiation deposits energy that produces <electron-hole pairs>; an applied <electric field> collects charge and the electronics convert it into a pulse. High-purity germanium instruments are useful for energy spectroscopy because a single absorbed photon can produce many charge carriers. Cooling reduces thermally generated carriers and electronic noise.<Radiation Detector Assembly by ORTEC>[pp.1–2: detector element, cryogenic enclosure and front-end electronics]{ref}
For a simple charge inventory, let deposited energy be $E$ and the mean energy per <electron-hole pair> be $w$. With complete charge collection,
$$
N\approx E/w,\qquad |Q|\approx eE/w.
$$
Using $w=2.96\,\mathrm{eV}$, the manufacturer's value at77K, an illustrative $E=59.2\,\mathrm{keV}$ deposit produces about20,000 pairs, corresponding to about $3.20\times10^{-15}\,\mathrm{C}$ of collected pulse charge. This is an average conversion, not a claim that every event produces exactly the same carrier count.<Radiation Detector Assembly by ORTEC>[p.2, Table1: energy per pair]{ref}
The apparatus therefore needs more than a piece of germanium: contacts establish a collecting field, a cooled enclosure controls the environment, and a <charge-sensitive preamplifier> measures the small pulse. A <photopeak> corresponds to events depositing the full photon energy. Escaping radiation or incomplete charge collection can produce smaller pulses, so a pulse-height distribution must be interpreted with the detector geometry and response.<Radiation Detector Assembly by ORTEC>[pp.1–2: detector assembly and charge-sensitive front end]{ref}
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