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 keVE = 668 keV Crystal at room temperature, Read-out: APD at -23 °C K.S. Shah et al., IEEE NS/MIC/RTSD 2003  FWHM < 1.3 MeV

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

Spectrum of LaCl 3 :Ce Crystal at room temperature, Read-out: PMT at +20 °C  FWHM ~ 1.3 MeV

K.S. Shah et al., IEEE NS Vol. 50 (2003) 2410 Time resolution of LaBr 3 :Ce Time resolution depends on Ce dopant concentration 5% Ce

Manufacturer's view  limited crystal size (LaBr 3 : 1" x 2", LaCl 3 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 LaBr 3 crystal: ~ 30€ Scint. detector: ~ 1500€ + 300€/cm 3

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 cm 3 ) 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

Large position sensitive LaBr 3 :Ce detector AB ab A C B D E =  (E a...E D ) pos(x,y,z) = centroid of light distribution 5 cm 6 cm

Requires cooling to reduce noise

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 LaBr 3 and LaCl 3 crystals