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When their sensitive structures are based on a single Diode , they are called semiconductor diode detectors. When they contain many diodes with different functions, the more general term '''semiconductor detector''' is used. Semiconductor detectors have found broad application during recent decades, in particular for Gamma and X-ray Spectrometry and as Particle Detector s. SEMICONDUCTOR RADIATION DETECTOR In these detectors, Radiation is measured by means of the number of Charge Carrier s set free in the detector, which is arranged between two Electrode s. Ionising radiation produces free Electron s and Holes . The number of electron-hole pairs depends on the Energy transmitted by the radiation to the semiconductor. As a result, a certain number of electrons are transferred from the Valence Band to the Conduction Band , and an equivalent number of holes are created in the valence band. Under the influence of an Electric Field , electrons as well as holes travel to the electrodes, where they give rise to a pulse that can be measured in an outer Circuit . The holes travel into the opposite direction and can also be measured. The energy required for production of electron-hole-pairs is very low compared to the energy required for production of paired ions in a gas detector. Consequently, in semiconductor detectors the Statistical Variation of the pulse height is smaller and the energy Resolution is higher. As the electrons travel fast, the time resolution is also very good. Compared with Gas Ionization Detector s, the Density of a semiconductor detector is very high, and charged particles of high energy can give off their energy in a semicoductor of relatively small dimensions. SEMICONDUCTOR PARTICLE DETECTORS Most silicon Particle detectors work, in principle, by Doping narrow (usually around 100 micrometres wide) strips of Silicon to make them into Diodes . As charged particles pass through these strips, they cause small ionization currents which can be detected and measured. Arranging thousands of these detectors around a collision point in a Particle Accelerator can give an accurate picture of what paths particles take. Silicon detectors have a much higher resolution in tracking charged particles than older technologies such as Cloud Chambers or Wire Chambers . The drawback is that silicon detectors are much more expensive than these older technologies and require sophisticated cooling to reduce leakage currents (noise source) as well as suffer degradation over time from Radiation . SEE ALSO Particle Detector X-ray Spectroscopy |
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