BLM types

  • Plastic Scintillators
    • charged particles, gammas, neutrons
    • Read out:
      • photomultiplier
        • relative small gain
      • particle counting mode
        • higher sensitivity
        • larger dynamic range: from single particles to 10**7/s
    • radiation hardness
      • low: nach 1Mrad010**4 Gy light transmission reduced by 1/e=0.37 (disadvantage)
    • dimensions
      • cylindrical rod 2cm diameter x 10 cm length (typical)
    • puls (rough!)
      • puls hight: from 200mv to 1V
      • puls length: from 20 (to 50)ns
  • Liquid Scintillators
    • scintillator material in 1liter solvent
    • charged particles, gammas, neutrons
    • puls (rough!)
      • puls hight: as Pl. Scintillator
      • puls length: 10times longer than Pl. Scintillator -> dynamic range 10times smaller than for Pl. Scintillator
    • radiation hardness
      • 10times more radiation hard than Pl. Scintillator (due to simpler compoisition of L. Scintillator)
  • Aluminium coated Electron Multiplier
    • PMT with an Aluminium cathode
    • puls
      • fast rise time
      • high dynamic range
      • much lower sensitivity than PL. Scintillator
  • PIN diode
    • 10x10mm*2 with 0.1mm depletion zone (two face-to-face mounted PIN diodes)
      • with two PIN diodes in coincidence the low energy photons are separated from the charged particles
    • low detection efficiency due to dimensions
    • commercially available
    • puls
      • Mip -> 10**4 electron-hole pairs
  • BF_3 propartional tube
    • 10mm x 500mm glas tube filled with BF_3 gas in a polyethylen housing of 200mm diameter (<-moderation of the neutrons)
    • neutrons up to 100MeV, high crss section (1kbarn)
    • Count rate limeted lower than 10*4/s <- time to recharge the central wire
  • Ionization Chamber
    • charged particles
    • signal strength gis directly the absorbed dose in Gy (definition)
    • radiation hardness very good <- innert gas
    • puls
      • signal orders of magnitude smaller than with counting mode devices
      • slow signals <- 100 mus drift time
    • read out
      • current-to-voltage or current-to-frequency converter
      • 1ms slow
  • Optcal Fiber
    • material modification by absorbed dose
    • 1ns laser puls travals with 0.66c through the fiber and is reflected by colour centers produced by particles
    • good spatial resolution
    • slow (1s) due tu use of OTDR (optical time domain reflector)
  • all linear
  • Pl. Scintillator has highes rate and highest dynamic range
  • L. scintillator saturation at highes rate due to the slow integrating amplifier
  • Ionisation Chamber: signal strength lower by foctor 200 than the Pl. scintillator
  • PIN diode has 3 orders of magnitude lower than PL. scintillator

-- GeorgSchepers - 15 Oct 2008
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Topic revision: r1 - 2008-10-15, GeorgSchepers
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