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16 Cards in this Set
- Front
- Back
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Semiconducting energy gap |
1.1 eV for Silicon, the energy to produce electron-hole pair is a bit higher because some energy excites the lattice |
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Semiconductors vs gas detectors |
Same number of pairs produced by 1 micrometer of semiconductor and 1 cm thick gas detector. Also mobiloty allows fast charge collection. |
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Semiconductor detectors thickness |
300 micrometers |
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Why pn junctions and not just semiconductors |
Only doped semiconductors have enough charge carriers to overcome the thermal current that covers the signal. (10^8 vs 10^4 pairs produced in a detectorby thermal ionozation and ionization produced by MIP = minimum ionizing particle i. e. with low ionizing power) |
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Types and concentration of impurities for doped semiconductors |
Phosphorus, Arsenic as donors (n), Boron as acceptor (p) / about 10^17 cm^-3 |
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Working mechanism of a solid state pn detector |
Pn junction in inverse polarization (100 V) has an internal barrier potential in the same verse of the external voltage and e-h pairs produced generate a current that sums to the thermal leakage current of a few nA. |
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Common pn junction materials |
Si, Ge (77 K) or if you want higher stopping power GaAs or CdZnTe |
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How to track a particle with solid state detectors |
Use microstrip detectors, where the p side is divided into parallel strips that measure the signal in different channels allowing to identify also the position of the pair production with an accuracy of 3 micrometers. |
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Distribution of dE/dx in the detector (proportional to the signal) |
Landau distribution for the counting of e-h pairs produced, with a long tail (mean>mode) |
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Desired quality of the signal S |
S/N > 10 to 20. Can be limited lowering T and using radiation hard (resistent) materials. |
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What affects spatial resolution? |
Statistical fluctuations in energy loss due to physical processes, the configuration of the strips, readout pitch, electronic noise |
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CMS detector |
It's a microstrip tracker organized as a barrel with 4 internal layers and 6 external with silicon microstrips |
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What is alignment for? |
To align various parts of the detector in order to reach a higher spatial resolution. |
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What is an alignment procedure? |
Calculate the residuals between the expected hit and the real cluster position of a high momentum track (like cosmic rays). Then minimize the Chi^2 function to derive the geometric parameters to implement in the geometry of the detector. |
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What are pixel detectors? |
Similar to microstrips detectors but the semiconductor is segmented in silicon tiles instead of strips giving a space 2 dimensional resolution. Also they work with integrated electronics which allow fast readout. |
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Parameters of silicon detectors |
Resolution: about 10 micrometers (precise) Readout time: about 1 microsecond (the faster) Dead time: <10 microseconds (fast) |
