Crystals and related topics
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Transcript of Crystals and related topics
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Crystals and related topics
J. Gerl, GSI
NUSTAR Calorimeter
Working Group Meeting
June 17, 2005
Valencia
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Properties of scintillators
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Energy resolution of LaBr3:Ce
E = 60 keV E = 668 keV
Crystal at room temperature,
Read-out: APD at -23 °C
K.S. Shah et al., IEEE NS/MIC/RTSD 2003
FWHM < 2% @ 1.3 MeV
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Energy resolution limitations
(E/E)2 = 5.6·(1/N·) + Rsci2 + Rnoise
2
Photon statistics and quantum efficieny: N·
Crystal inhomogeinity, non-proportionality, light losses: Rsci
Electronic noise: Rnoise
Cooling to improve N and Rnoise?
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Spectrum of LaCl3:Ce
Crystal at room temperature,
Read-out: PMT at +20 °C
FWHM ~ 2% @ 1.3 MeV
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K.S. Shah et al., IEEE NS Vol. 50 (2003) 2410
Time resolution of LaBr3:Ce
Time resolution depends on Ce dopant concentration
5% Ce
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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
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Size considerations
Facts:
Full light collection requires Length / Diameter < 3
Cost / Volume decreases with detector size
Cost / Volume increases with surface area
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
Long conical crystals are not appropriate
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Large position sensitive LaBr3:Ce detector
A B
a b
A
C
B
D
E = (Ea...ED)
pos(x,y,z) = centroid of light distribution
5 cm
6 cm
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Requires cooling to reduce noise
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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
14x14 pixel APD
APDs from Radiation Monitoring Devices Inc.
RMD produces also LaBr3 and LaCl3 crystals