Lead Tungstate Crystals for the CMS Electromagnetic Calorimeter at the LHCIoan DafineiI.N.F.N. Sezione di Roma, Rome ITALY(on behalf of CMS ECAL Collaboration)

IndexIntroductionPWO General PropertiesLuminescence SpectrumScintillation characteristicsRadiation hardnessPWO for ECAL-CMSR&D Short ReviewRequisites & Qualification ParametersRegional CentersPreproduction Crystal Properties Present StatusRecent Developments in PWO Crystal Growth TechnologyConclusions

IntroductionRequirements for scintillators to be used for ECAL construction high density and high Z mechanical ruggedness chemical stability uniformity of properties low pricetechnological requirementshigh stopping powerhigh granularityhigh energy resolutionLuminosity 1034 cm-2s-1Bunch separation 25 ns

Introduction

PWO General PropertiesPWO Crystal Growth

PWO General PropertiesLuminescence Spectrum

PWO General PropertiesScintillation Characteristics

PWO General PropertiesScintillation Characteristics

PWO General PropertiesRadiation Hardnesslight production is not affectedcreation of color centres is quenched by appropriate doping

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

R&D Short ReviewGoals of Pre-production ActivityFor Producer : Increase the rate of production Improve the crystal quality and homogeneity of propertiesFor CMS-ECAL communitySetting 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 CERN800 re-measured on ACCOR at Rome (ACCOS-ACCOR intercalibration)

Requisites & Qualification ParametersQualification parametersLight Yield LY@8X0 8 pe/MeV at 18C-0.35 %/X0 FNUF +0.35 %/X0 LY(100ns)/LY(1ms) > 90% LY@8X0 =7.5a+b FNUF =100(-0.89a)/(11.5a+b)

Requisites & Qualification ParametersQualification parametersTransmissionLT360nm 25%LT420nm 55%LT620nm 65%LTslopeinflection > 3%/nm dlTT=50% 3nmCheck general quality and radiation resistanceT=p2exp(-(p3)/w-exp((p0-w)p1))

Requisites & Qualification ParametersQualification parametersDimensiosdimensions within +0.00 mm , -0.10 mm of nominal valuesplanarity for all faces within 0.02 mmchamfers between 0.3 mm and 0.7 mmpolished faces with roughness < 0.020 mmunpolished face with roughness = 0.350 mm

Regional CentersCERN Lab.27 Regional Centerhttp://cmsdoc.cern.ch/cms/ECAL/html/wp/rc/

Regional CentersRome, Italy Regional Centerhttp://www.roma1.infn.it/exp/cms/

Regional CentersACCOS-ACCOR Intercalibration

Regional CentersACCOS-ACCOR IntercalibrationsR-C=1.4%sR-C=0.8%sR-C=0.5%

Regional CentersACCOS-ACCOR Intercalibration

Regional CentersACCOS-ACCOR Intercalibration

Pre-Production Crystal Properties

Pre-Production Crystal PropertiesPre-Production in ChinaTransmission characteristics

Pre-Production Crystal PropertiesBatch 1 to 7 depolished face +0.2Batch 8 to 14 depolished face +0.39

Pre-Production Crystal PropertiesPre-Production in ChinaLight production characteristics

Pre-Production Crystal PropertiesFront irrad., 1.5Gy, 0.15Gy/hLYloss=(LY0-LYirr)/LY0 (%)

Pre-Production Crystal Properties

Pre-Production Crystal PropertiesPre-Production in ChinaRadiation hardness characteristics

Pre-Production Results 6000 Crystals produced by BTCPSept. 1998 to Dec. 2000

Production ScheduleTo be produced before end 2004 :56000 crystals for Barrel16000 crystals for EndcapsPresent status :6000 preproduction crystals2000 production crystalsStarted in 2001

Recent DevelopmentsCrystal Growth Technology Steps

Recent DevelopmentsF = 65 mmPWO crystals made in BTCP Bogoroditsk

Recent DevelopmentsLarge PWO crystals made in BTCP Bogoroditskscintillation characteristics

Recent Developmentssaturation doseradiation hardnesslongitudinal uniformityLarge PWO crystals made in BTCP Bogoroditsk

Recent Developmentsradiation hardnessradial uniformityLarge PWO crystals made in BTCP Bogoroditsk

Recent Developmentsradiation hardnessLarge PWO crystals made in BTCP Bogoroditsk

New vs Old Technology

New vs Old Technology

New vs Old Technology

Conclusions Success of the R&D phaseIncrease of the production rategood 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 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

ConclusionsReady to Construct the CMS-ECAL&

Claims:Given the CMS goals, LHC working conditions and budget constraints, PbWO4 (PWO) crystal was the best choice among other possible candidates for the construction of the ECAL.PWO properties make it be a very special scintillator. The co-existence of several scintillation centres allows for a tuning of the emission peak and decay time which is an advantage for the one who is looking for new applications of PWO scintillators. It may be instead a fearsome drawback for who wants to freeze these properties once the application was chosen. More, the quenched character of PWO luminescence at room temperature results in a poor light yield with a relatively high temperature coefficient which add supplementary complications to the definition and further check of PWO scintillator qualification parameters.An important R & D effort was necessary in order to guarantee the production of PbWO4 crystals able to satisfy the challenging constraints imposed for CMS-ECAL contsruction. This effort was doubled by a technological effort aimed at creating the conditions to qualify PWO crystals for ECAL-CMS use in industrial quantities. The performance of the pre-production crystal batches (about 6000 barrel crystals) is consistent with the very strict quality parameters defined by the ECAL Collaboration.Recent developments in the PbWO4 crystals growth technology may speedup the crystal supplying for the ECAL construction.The R&D actvity aimed at tuning PWO properties to the ECAL-CMS constraints made attainable the production of PWO crystals with uniform optical properties at industrial scale. PWO growth technology for ingots up to 65mm in diameter is now well under control. Further increase of the diameter and application of this technology to endcap crystals, are feasible.

Two main components are present in the emission spectrum of PbWO4 crystals: blue componentpeak @ 420 nmascribed to a regular lattice centre (WO4)2-green componentpeak @ around 480 - ascribed toa defect centre WO3impurity (MoO4)2-raspite-type inclusions existing in synthetic PWO crystals (usually scheelite)

PWO:Mo(PW-95b 160 ppm), XeCl-laser excit., RT

Spectrally unresolved scintillation decay of undoped PbWO4 excit. 22Na (511 keV), 295 K