Silicon drift detector
Silicon drift detectors are X-ray radiation detectors used in x-ray spectrometry (EDXRF) and electron microscopy (EDX). Their chief characteristics compared with other X-ray detectors are:
  • high count rates
  • comparatively high energy resolution (e.g. 140 eV for Mn K wavelength)
  • Peltier cooling

Working principle

Like other solid state X-ray detectors, silicon drift detectors measure the energy of an incoming photon by the amount of ionization it produces in the detector material. In the SDD, this material is high purity silicon with a very low leakage current. The high purity allows for the use of Peltier
Jean Charles Athanase Peltier
Jean Charles Athanase Peltier ]] – October 27, 1845, in Paris) was a French physicist.He discovered the calorific effect of electric current passing through the junction of two different metals...

 cooling instead of the traditional liquid nitrogen. The major distinguishing feature of an SDD is the transversal field generated by a series of ring electrodes that causes charge carriers to 'drift' to a small collection electrode. The 'drift' concept of the SDD (which was imported from particle physics) allows significantly higher count rates coupled with a very low capacitance of the detector.

In older detector designs, the collection electrode is centrally located with an external FET (field effect transistor) to convert the current into a voltage and thus represents the first stage of amplification. Newer designs integrate the FET directly into the chip, which greatly improves energy resolution and throughput. This is due to the reduction of capacitance between anode and FET, which reduces electronic noise.

Other designs move the anode and FET outside of the irradiated area. This causes a slightly reduced response time, which leads to a slightly lower throughput (750,000 counts per second instead of 1,000,000). However, due to the smaller anode size, this leads to better energy resolutions (down to 123 eV for Mn Kα wavelength). Combined with improved or adapted signal processing, it is possible to maintain the Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

drift detector's energy resolution up to 100,000 counts per second.
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