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Crystals and related topics

Crystals and related topics. J. Gerl, GSI NUSTAR Calorimeter Working Group Meeting June 17, 2005 Valencia. Properties of scintillators. Energy resolution of LaBr 3 :Ce. E = 60 keV. E = 668 keV. Crystal at room temperature, Read-out: APD at -23 ° C.  FWHM < 2% @ 1.3 MeV.

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Crystals and related topics

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  1. Crystals and related topics J. Gerl, GSI NUSTAR Calorimeter Working Group Meeting June 17, 2005 Valencia

  2. Properties of scintillators

  3. Energy resolution of LaBr3:Ce E = 60 keV E = 668 keV Crystal at room temperature, Read-out: APD at -23 °C  FWHM < 2% @ 1.3 MeV K.S. Shah et al., IEEE NS/MIC/RTSD 2003

  4. Energy resolution limitations Photon statistics and quantum efficieny: N· Crystal inhomogeinity, non-proportionality, light losses: Rsci Electronic noise: Rnoise (E/E)2 = 5.6·(1/N·) + Rsci2 + Rnoise2  Cooling to improve N and Rnoise?

  5. Spectrum of LaCl3:Ce Crystal at room temperature, Read-out: PMT at +20 °C  FWHM ~ 2% @ 1.3 MeV

  6. Time resolution of LaBr3:Ce Time resolution depends on Ce dopant concentration 5% Ce K.S. Shah et al., IEEE NS Vol. 50 (2003) 2410

  7. Manufacturer's view • limited crystal size (LaBr3: 1" x 2", LaCl3 3" x 3") • very hygroscopic → sealed housing, glass window? • hard and brittle → cutting and polishing problematic • Best suited for medical imaging → Attractive market Crystal treatment is expensive Lot of development is going on Costs: Raw LaBr3 crystal: ~ 30€ Scint. detector: ~ 1500€ + 300€/cm3

  8. Size considerations Facts: Full light collection requires Length / Diameter < 3 Cost / Volume decreases with detector size Cost / Volume increaseswith surface area Long conical crystals are not appropriate Options: 1. Build blocks of small (~ 1 cm3) cubes read-out by PIN-diodes or APDs 2. Build position sensitive detectors of large size read-out by several PMTs or APDs

  9. Large position sensitive LaBr3:Ce detector 5 cm D C A B A B 6 cm E =  (Ea...ED) a b pos(x,y,z) = centroid of light distribution

  10. Requires cooling to reduce noise

  11. APDs from Radiation Monitoring Devices Inc. 14x14 pixel APD • Features • Gain above 1,000 at operating condition of best signal-to-noise ratio. (Maximum gain of 10,000.) • Large active area • High quantum efficiency (QE) extends beyond visible spectrum • High speed at 1064 nanometer wavelength of YAG lasers • Pulse counting mode is the most-frequent style of use. • Optical Photon Counting (2-3 photons) when cooled RMD produces also LaBr3 and LaCl3 crystals

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