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DETECTOR TECHNOLOGIES Lecture 4 : Radiation Detectors - Scintillation - Čerenkov - TRD

DETECTOR TECHNOLOGIES Lecture 4 : Radiation Detectors - Scintillation - Čerenkov - TRD. Scintillation : principles. Scintillator : a material which emits light (photons), when stimulated. Of course, we need a light sensor to transform the light in an electric signal.

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DETECTOR TECHNOLOGIES Lecture 4 : Radiation Detectors - Scintillation - Čerenkov - TRD

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  1. DETECTOR TECHNOLOGIES Lecture 4 : Radiation Detectors - Scintillation - Čerenkov - TRD

  2. Scintillation : principles Scintillator: a materialwhichemits light (photons), whenstimulated Of course, weneed a light sensor to transform the light in an electric signal  ≈ nsec. - µsec. Fluorescence  ≈ µsec. - minsPhosphorescence Light intensity : Read out Photo detector Scintillator Ligth guide

  3. Scintillation : principles For a scintillator, whatis important ? - Scintillation efficiency: energyneeded for 1  - emission - Light spectrum: in order to adapt the read out system to the proper wavelength - Light decay time -  absorption - Transparency: the emitted  should not bere-absorbed. 2 types of scintillators : Organics (liquids, plastics) Inorganics (crystals,liquids) Advantage : FastAdvantages : good efficiency Disadvantages : ratherinnefficients good linearity non-linear (needquenching) radiation tolerance not good for  ‘s Disadvantages : relatively slow expensive (if crystals) Usedmainly for trigger purposeUsedmainly for measurements

  4. Scintillation : Organicscintillators • Excitation of organicmolecules • Yield≈ 1  per loss of 100 eV •  λ ≈100 nm (UV) • Absorption and re-emission •  λ≈300 nm (UV) • Absorption and re-emission •  λ≈ 400 nm (Blue) OrganicScintillators : Waveshifter (adapts to the read-out) slows the process induce a non-linearity Luminescence (Birk’slaw) per lenght S = emissionefficiency KB = Birk’s constant (exp.) Low Z (organic = Hydrogen + Carbon) lowefficiency for HE  (only Compton effect) but good efficiency for neutrons

  5. Scintillation : Organicscintillators Wavelenght shift

  6. Scintillation : Inorganicscintillators : crystals Crystals (NaI, CsI, BGO, PbWO4…) Energylosswillinduceelectron-hole pairs creation migration to activation centers (fast) - excitation – transition -  emission trapping (slow) Activatorischoosen for visible emission 2 or more wavelenghts (addition of activator) Liquid noble gases (Lar, Lxe, LKr) Still 2 time constants Samewavelengths (pure gases) Precisionmeasurements

  7. Scintillation : Inorganicscintillators Inorganiccrystals are temperature-sensitive (calorimeters have to becooled)

  8. Scintillation : Inorganicscintillators

  9. Scintillation : Transport of light The readout has to be adapted to geometry and emission spectrum of the scintillator. Light guide Total reflection inside the light guide Material : PPMA (Polymethylmethacrylat) Plexiglas (C5O2H8)n

  10. Scintillation : Transport of light Optical fiber Improved aperture with multi-cladding

  11. Scintillation : Transport of light Scintillatingfiber : opticalfiberfilledwithscintillator (plastic or liquid) Stack of SciFibers (UA2)

  12. Scintillation : Photodetector Photodetector : Convert the scintillatingligthinto usable electronic signal (HE Physics : usually visible and UV spectrum) = Convert UV and visible photons in electrons Requirement : High conversion efficiency QE = N photo-electrons / N photons

  13. Scintillation : Photomultiplier

  14. Scintillation : Photomultiplier Requirement : High conversion efficiency QE = N photo-electrons / N photons Total gain : Resolution : linearity statistics And … Sensitivity to magneticfield δ = N electronsproduced / N electronsincoming n = number of dynodes

  15. Scintillation : Photomultiplier

  16. Scintillation : Photomultipliersevolutions Multi anode PMT Resistant to magneticfield

  17. Scintillation : HPD Hybrid Photo Diode (HPD) highlysegmentedread out Good sensitivity (PMT like) Speed Lesssensistive to Mag. Field Precision

  18. Scintillation : HPD LHCb : Cerenkovsread-out with HPDS

  19. Scintillation : HPD Cms /HCAL read-out withHPDs

  20. Scintillation : APD Avalanche Photo Diode (APD) : an all-silicondevice. - high photo conversion Q eff≈ 0.7 - Very high electricfield 10 5 V/m(avalanche mode) - Thick - Linear mode Good tolerancewithmag. Field good (?) tolerance to radiation

  21. Scintillation : APD CMS APDs : ≈ 141 500 Pieces for the ECAL (scintillator : PWBO4) Active size : 5 x 5 mm2

  22. Scintillation : SiPM PPD : Pixelized Photon Detector = SiPM : SiliconPhotomultplicator = APDs in parallelwithresistors - high photo conversion Q eff≈ 0.7 - Very high Gain (10 5) - Geiger mode - Pixelized - Not a proportionalcounter - Very good position counter - Adapted to fibers (small surface)

  23. Scintillation : SiPM

  24. Scintillation : SiPM

  25. Scintillation : Photomultiplier

  26. Čerenkov Čerenkov Detectors Particle travelling fasterthan light in a given medium emits radiation (photons) and The emission of Čerenkov light depensdirectlyfrom the speed of the particle depensindirectlyfrom the mass of the particle The maximum angle depensonlyfrom the medium. Typical : 0.35 µm < λcerenkov< 0.55 µm (usual medium : 1 < n < 2)

  27. Čerenkov Radiation intensity (Franck-Tamm formula) : α = 1 / 137 λ = Cerenkov light θ = Cerenkov angle For a charged (1) particle,  = 1

  28. ThresholdČerenkov ThresholdCrenekovdetectors make a simple decision on wether the particle isabove or below the Cerenkovthresholdvelocity. Used for differentiatingheavyparticles (π, K, p) Changing the thegas pressure Changes the refractive index

  29. ThresholdČerenkov Aerogel : silicate gel (99.8% Air)

  30. ThresholdČerenkov

  31. RICH Čerenkov Ring Imaging Cherenkov (Ypsilantis and Seguinot -1977)

  32. RICH Čerenkov The LHCb RICH C 4 F 10 in RICH 1 (n = 1.0014) CF 4 in RICH 2 (n = 1.005) Read-out : HPDs

  33. RICH Čerenkov

  34. Transition Radiation Detector Transition radiationis a photon emission (X) occuringwhen a charged particle passes through inhomogeneous media, such as a boundary between two different media with different dielectric properties Emission at an angle Verylow rate

  35. Transition Radiation Detector ALICE TRD

  36. Transition Radiation Detector ALICE TRD

  37. Transition Radiation Detector ATLAS TRT : CombinationTracker / TRD About 300 000 Straw tubes : position measurement by dE/dX radiation occurs on the wall of the tube

  38. Transition Radiation Detector ATLAS TRT : CombinationTracker / TRD About 300 000 Straw tubes : position measurement by dE/dX radiation occurs on the wall of the tube

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