Lecture Notes (17 pages)

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Lecture Notes



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Lecture Notes

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Lecture Notes


Pages:
17
School:
University of Texas at Arlington
Course:
Phys 3446 - Nuclear and Particle Physics
Nuclear and Particle Physics Documents

Unformatted text preview:

PHYS 3446 Lecture 18 Wednesday Oct 29 2008 Dr Andrew Brandt 1 Particle Detection Scintillation Counters Time of Flight Cerenkov Counter Grades are posted please review them Lowest 1 Q and 1 HW dropped Olsen colloquium on Higgs and Mass at 4pm cookies at 3 30 Wednesday Oct 29 2008 PHYS 3446 Fall 2008 Andrew Brandt 1 Scintillation Counters Ionization produced by charged particles can excite atoms and molecules in the medium to higher energy levels The subsequent de excitation process produces light that can be detected and provide evidence for the traversal of the charged particles Scintillators are material that can produce light in visible part of the spectrum Wednesday Oct 29 2008 PHYS 3446 Fall 2008 Andrew Brandt 2 Scintillation Counters Two types of scintillators Organic or plastic Tend to emit ultra violate Wavelength shifters are needed to reduce attenuation Faster decay time 10 8s More appropriate for high flux environment Inorganic or crystalline NaI or CsI Doped with activators that can be excited by electron hole pairs produced by charged particles in the crystal lattice These dopants can then be de excited through photon emission Decay time of order 10 6sec Used in low energy detection Wednesday Oct 29 2008 PHYS 3446 Fall 2008 Andrew Brandt 3 Scintillation Counters Photo multiplier Tube The light produced by scintillators are usually too weak to see Photon signal needs amplification through photomultiplier tubes Light can pass directly from scintillator to PMT or else through a light guide Photocathode Made of material in which valence electrons are loosely bound and subject to photo electric effect Series of multiple dynodes that are made of material with relatively low work function Operate at an increasing potential difference 100 200 V difference between dynodes Wednesday Oct 29 2008 PHYS 3446 Fall 2008 Andrew Brandt 4 Scintillation Counters Photomultiplier Tube The dynodes accelerate the electrons to the next stage amplifying the signal by a factor of



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