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Lead Tungstate Crystals for the CMS Electromagnetic Calorimeter at the LHC

Lead Tungstate Crystals for the CMS Electromagnetic Calorimeter at the LHC. Ioan Dafinei I.N.F.N. Sezione di Roma, Rome ITALY (on behalf of CMS ECAL Collaboration). Index. Introduction PWO General Properties Luminescence S pectrum Scintillation characteristics Radiation hardness

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Lead Tungstate Crystals for the CMS Electromagnetic Calorimeter at the LHC

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  1. Lead Tungstate Crystals for the CMS Electromagnetic Calorimeter at the LHC Ioan Dafinei I.N.F.N. Sezione di Roma, Rome ITALY (on behalf of CMS ECAL Collaboration)

  2. Index • Introduction • PWO General Properties • Luminescence Spectrum • Scintillation characteristics • Radiation hardness • PWO for ECAL-CMS • R&D Short Review • Requisites & Qualification Parameters • Regional Centers • Preproduction Crystal Properties Present Status • Recent Developments in PWO Crystal Growth Technology • Conclusions

  3. Requirements for scintillators to be used for ECAL construction small X0 LHC small Rm large LY high refractive index short dead time fast ECAL-CMS radiation hard emission spectrum overlapping with spectral sensitivity of commonly used photodetectors Introduction high stopping power high granularity high energy resolution high density and high Z Bunch separation 25 ns Luminosity 1034 cm-2·s-1 • mechanical ruggedness • chemical stability • uniformity of properties • low price technological requirements

  4. r (g/cm3) 8.26 X0 (cm) 0.89 Rm (cm) 2.2 PbWO4 (PWO) Studied as scintillator since 1979 t (ns) 15 lemission 420 n@ lemission 2.29 Workshop on tungstate crystals LY 2 % LYtemp.coeff. -2%/°C SCINT Conferences Introduction

  5. PWO Crystal Growth Bogoroditsk Techo Chemical Plant, Russia Shanghai Institute of Ceramics, China 1123° seed Liquid 1100 Czochralski method 1000 970° 935° 66.5% 915° grown crystal 900 37% 800 740° 730° 700 16.5% molten PWO 2:1 1:1 PWO3 PWO4 PbO WO3 RF heating Chang, 1971 20 40 60 80 Bridgman method mole % PWO General Properties

  6. Luminescence Spectrum PWO1185 PWO1180 PWO1168 blue component Pb2+ WO42- c c c green component a a a (MoO4) 3- WO43- (WO6) 6- PWO General Properties

  7. Scintillation Characteristics Photoluminescence decay Spectrally unresolved scintillation a=100·(Iss/Itot) (%) Itot Iss lexc=308 nm (XeCl excimer laser) I(t)=0.5·exp(-t/3ns)+0.07·exp(-t/12ns)+0.008·exp(-t/102ns) PWO General Properties

  8. Scintillation Characteristics 1400 1200 light yield (a.u.) 1000 300 temp.coeff.(%/°C) 800 250 0 600 200 -1 light yield (a.u.) temperature (°C) -2 400 150 -3 a20°C = -1.98%/°C I.Dafinei, Mat.Res.Soc. Vol.348(1994), p.99 -4 200 100 -5 0 50 -40 -20 0 20 40 60 -200 -150 -100 -50 0 50 temperature (°C) PWO General Properties

  9. Radiation Hardness PWO General Properties • light production is not affected • creation of color centres is quenched by appropriate doping

  10. Theoretical transmission 100 '98 crystal Transmission (%) 80 60 '95 crystal 40 20 1998 1995 0 Wavelength (nm) 300 350 400 450 500 550 600 650 700 R&D Short Review • 1992 : Crystal2000 Conference • 1994 : choice of PWO for CMS-ECAL • 1994-1998 : R&D phase • 1998-2000 : Pre-Production of 6000 crystals • 2001 : Start of the Production

  11. Goals of Pre-production Activity R&D Short Review • For Producer : • Increase the rate of production • Improve the crystal quality and homogeneity of properties • For CMS-ECAL community • Setting up the Regional Centres • Installation of Automatic Crystal Control System (ACCOS) • (machines designed to make the full characterisation of 30 crystals in 7 hours) All the 6000 crystals have been measured on ACCOS at CERN 800 re-measured on ACCOR at Rome (ACCOS-ACCOR intercalibration)

  12. Qualification parameters Light Yield LY(x)= a · x+b Requisites & Qualification Parameters LY@8X0=7.5·a+b FNUF =100·(-0.89·a)/(11.5·a+b) • LY@8X0 8 pe/MeV at 18°C • -0.35 %/X0 FNUF  +0.35 %/X0 • LY(100ns)/LY(1ms) > 90%

  13. Qualification parameters Transmission TT LT LT TT Requisites & Qualification Parameters T=p2·exp(-(p3)/w-exp((p0-w)·p1)) • LT360nm 25% • LT420nm 55% • LT620nm 65% • LTslopeinflection > 3%/nm •  dlTT=50% 3nm Check general quality and radiation resistance

  14. Qualification parameters Dimensios ! ECAL-CMS Requisites & Qualification Parameters • dimensions within +0.00 mm , -0.10 mm of nominal values • planarity for all faces within 0.02 mm • chamfers between 0.3 mm and 0.7 mm • polished faces with roughness < 0.020 mm • unpolished face with roughness = 0.350 mm

  15. CERN Lab.27 Regional Center ACCOCE Light yield uniformity CERN Lab.27 EP-CMA Transmission Dimensions Regional Centers http://cmsdoc.cern.ch/cms/ECAL/html/wp/rc/

  16. Rome, Italy Regional Center ACCOR Dark room temperature : 20±0.5°C rel. humidity: 50±10% Dimensions Co60 LED Casaccia Coord3 S.p.A. Light yield uniformity PM Transmission Capacity: 35 crystals/run 1 run time: approx. 10 hours Regional Centers http://www.roma1.infn.it/exp/cms/

  17. ACCOS-ACCOR Intercalibration LY>8pe/MeV Measure 2-3 pe ! -0.35<FNUF(%/Xo)<+0.35 sR-C=0.8pe/MeV sR-C=0.19%/Xo Regional Centers

  18. ACCOS-ACCOR Intercalibration LT@360nm 60 LT@620nm 50 80 LT@420nm 75 40 CernLT@360 30 75 CernLT@620 70 CernLT@420 20 10 70 65 0 0 10 20 30 40 50 60 RomeLT@360 65 65 70 75 80 60 60 65 70 75 RomeLT@620 RomeLT@420 Regional Centers sR-C=1.4% sR-C=0.8% sR-C=0.5%

  19. ACCOS-ACCOR Intercalibration Inflection Wavelength LT slope@inflection 4 359 TT spread at 50% 4 Cern 357 3.5 3.5 Rad hard check 3 Cern S@infl (%/nm) 2.5 353 3 Roma TTsp (nm) 2 1.5 2.5 349 1 Cern TTsp (nm) 0.5 2 345 0 2 2.5 3 3.5 4 345 349 353 357 0 0.5 1 1.5 2 2.5 3 3.5 4 Rome Rome S@infl (%/nm) sR-C=0.15%/nm sR-C=0.15%/nm Regional Centers

  20. ACCOS-ACCOR Intercalibration AR Statistics made on 373 Xtals BR AF BF CR CF Regional Centers

  21. batch 1 10 Mean: 61.88% StDev. : 7.5% 8 100 6 Number of crystals Longitudinal Transmission (%) 90 4 80 batch 8 2 70 60 250 0 75 30 35 40 45 50 55 60 65 70 80 Mean: 69.01% Transmission at 420nm (%) 50 200 StDev. : 1.59% 40 Wavelength (nm) 150 30 1400 6000 crystals 100 20 1200 10 50 batch 14 1000 150 55% 0 Mean: 70.07% 800 0 700 300 350 400 450 500 550 600 650 30 40 50 55 60 75 80 35 45 65 70 no.of Xtals Transmission at 420nm (%) StDev. : 1.46% 600 100 400 200 50 0 30 35 40 45 50 55 60 65 70 75 80 Transmission at 420nm (%) 0 30 35 40 45 50 55 60 65 70 75 80 Transmission at 420nm (%) 11.04.01 Pre-Production Crystal Properties

  22. Pre-Production in China 18 16 14 12 10 # crystals 45 8 40 6 35 4 30 2 0 10 20 30 40 50 60 70 80 40 25 0 # crystals 20 35 20 LT@360nm (%) 15 18 30 16 10 25 14 5 20 # crystals 12 0 10 # crystals 15 0 10 20 30 40 50 60 70 80 8 10 6 LT@620nm (%) 5 4 2 0 0 0.1 1.1 2.1 3.1 0.2 2.2 4.2 6.2 8.2 10.2 16 Slope@infl (%/nm) TTspread@50% (nm) 14 12 10 8 # crystals Statistics made on 100 crystals 6 4 2 0 0 10 20 30 40 50 60 70 80 LT@420nm (%) Pre-Production Crystal Properties Transmission characteristics

  23. 350 LY@8X0 FNUF 300 500 250 200 400 150 300 100 50 200 0 -1.5 -1 -0.5 0 0.5 1 1.5 2 NuF Front (%/Xo) 100 1400 1200 FNUF 0 1200 LY@8X0 LY@8X0 (pe/MeV) 0 1 3 6 9 10 11 12 13 14 16 2 4 5 7 8 15 1000 1000 800 800 600 600 400 400 200 200 0 0 1 4 8 10 11 12 14 16 0 2 3 5 6 7 9 13 15 -1.5 -1 -0.5 0 0.5 1 1.5 2 LY@8X0 (pe/MeV) NuF Front (%/Xo) Pre-Production Crystal Properties Batch 1 to 7 <Ra> depolished face +0.2 Batch 8 to 14 <Ra> depolished face +0.39

  24. Pre-Production in China 35 30 25 20 # crystals LY@8X0 (ACCOS measured) 15 10 5 0 0 2 4 6 8 10 12 14 16 LY (p.e./MeV) Statistics made on 100 crystals Pre-Production Crystal Properties Light production characteristics

  25. LYirr/LY0 (%) Pre-Production Crystal Properties Front irrad., 1.5Gy, 0.15Gy/h LYloss=(LY0-LYirr)/LY0 (%)

  26. N = 32 Xtals StDev : 1.21%Mean: 3.39% batch 1 10 Front irrad., 1.5Gy, 0.15Gy/h 8 100 6 4 Statistics on 368 crystals Mean : 2.45 % StDev : 1.06% 80 LY loss (%) 2 20 60 0 N = 33Xtals batch 8 16 StDev : 0.9%Mean: 1.92% 40 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 12 Rejected for LTslope < 1.5%/m Rejected for LT@350nm < 10% 8 20 20 4 StDev : 1.21%Mean: 0.92% N = 19Xtals 0 16 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 LY loss (%) 12 batch 14 8 LY loss (%) 4 0 LY loss (%) Pre-Production Crystal Properties

  27. Pre-Production in China Change of total light output during front irradiation at 0.15 Gy/h data for 21 crystals LYirr/LY0 (%) Pre-Production Crystal Properties Radiation hardness characteristics

  28. 50 Dimensions Transmission 1000 Planning Delivered 40 Light Yield Decay time 800 30 Slope/Rad.hardness 600 20 400 10 200 0 0 set-98 set-99 set-00 dic-98 dic-99 dic-00 giu-99 giu-00 mar-99 mar-00 set-00 set-99 set-98 dic-98 dic-99 dic-00 giu-99 giu-00 mar-99 mar-00 yield Xtals quality Increased Improved production rate stability of parameters Pre-Production Results Sept. 1998 to Dec. 2000 6000 Crystals produced by BTCP

  29. increased productivity is needed New crystal development : Ingot diameter increase Production Schedule Started in 2001 • Present status : • 6000 preproduction crystals • 2000 production crystals • To be produced before end 2004 : • 56000 crystals for Barrel • 16000 crystals for Endcaps

  30. Barrel Endcap Barrel 32 mm 44 mm 65 mm 1996 1999 End 2000 Recent Developments Crystal Growth Technology Steps

  31. F = 32 mm Recent Developments PWO crystals made in BTCP Bogoroditsk F = 65 mm

  32. time (ns) % 30.0 80.3 A. N. Anenkov et all, Scint2001 Conference 50.0 89.9 100.0 96.4 300.0 99.3 1000.0 99.9 1525.5 99.9 Recent Developments Large PWO crystals made in BTCP Bogoroditsk scintillation characteristics

  33. A. N. Anenkov et all, Scint2001 Conference Recent Developments Large PWO crystals made in BTCP Bogoroditsk radiation hardness longitudinal uniformity saturation dose

  34. center side A. N. Anenkov et all, Scint2001 Conference Recent Developments Large PWO crystals made in BTCP Bogoroditsk radiation hardness radial uniformity

  35. PWO 7365 1st irradiation at the Geneve Hospital 100 60Co 430 Gy 80 Transmission (%) 60 40 1i1 1irr1 Irr1 + 20' 20 Irr1 + 40' Irr1 + 24h 0 300 350 400 450 500 550 600 650 700 Wavelength (nm) Recent Developments Large PWO crystals made in BTCP Bogoroditsk radiation hardness

  36. LT@360 N = 300 60 Mean: 31.36% LT@420 N = 300 StDev : 3.3% Mean: 69.91% counts 50 StDev : 0.85% Batch P2 from CERN/ISTC production contract #1718 was used to compare: • 260 barrel crystals produced with the standard technology • 40 barrel crystals produced with the new technology 40 counts 30 20 10 Transmission at 360nm (%) 0 140 0 30 5 35 10 15 40 20 45 25 30 50 35 55 40 60 45 50 65 55 70 60 65 75 70 80 Transmission at 420nm (%) 120 100 80 60 40 20 0 New vs Old Technology

  37. 260 barrel crystals produced with the standard technology 40 barrel crystals produced with the new technology LT slope@inflection LY@8X0 N = 300 crystals 300 140 N = 300 crystals Mean : 3.30%/nm 120 250 StDev : 0.06%/nm Mean : 9.1 pe/MeV counts 100 StDev : 0.57 pe/MeV 200 counts 80 150 60 100 40 50 20 0 0 Slope@inflection (%/nm) 5 6 7 8 9 10 11 12 13 14 0 1 2 3 4 5 6 7 8 9 10 Light Yield (pe/MeV) New vs Old Technology

  38. Front irrad., 1.5Gy, 0.15Gy/h New vs Old Technology

  39. Conclusions • Present status of physics and technology of scintillating materials shows that the CMS Collaboration decision to use PWO crystals for the ECAL construction was the best possible choice • Success of the R&D phase • Increase of the production rate • good quality crystals • uniform optical properties • Technology for ingots up to 65mm diameter is now well under control • The possibility to further increase the as grown PWO diameter and to apply this approach to endcap crystals is realistic

  40. CERN Lab.27 EP-CMA Casaccia 1st module of 400 crystals build in 2001 for ECAL Conclusions & Ready to Construct the CMS-ECAL

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