Abstract

Lead tungstate (PbWO4, or PWO) scintillating crystals are used by two of the four experiments at the Large Hadron Collider (LHC): 75848 in CMS and 17920 in ALICE. For the CMS electromagnetic calorimeter, one of the most important crystal properties is its radiation hardness. With the increase of luminosity, the radiation level will increase drastically, particularly in the high pseudorapidity regions of the calorimeter. Beside the effects of color-centre formation caused by γ-radiation, additional measurable effect originated by hadron irradiation could appear, which will further deteriorate the optical transmission of the crystals and therefore their efficiency. In this paper, we will present results of the proton-induced damage in PWO and a study of optical transmission recovery at different temperatures and under different light-induced “bleaching” conditions for proton-irradiated crystals.

Highlights

  • The CMS Electromagnetic Calorimeter ECAL made of 75848 lead tungstate crystals (PbWO4, PWO) was designed in 1994 for an integrated luminosity of 500fb-1 to be achieved in 2020 [1]

  • Beside the effects of color-centre formation caused by γ-radiation, additional measurable effect originated by hadron irradiation could appear, which will further deteriorate the optical transmission of the crystals and their efficiency

  • Beside the effects of colour-centre formation caused by γradiation, additional measurable effects produced by hadronic interactions with nuclei of the PWO crystals have to be accounted for

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Summary

INTRODUCTION

The CMS Electromagnetic Calorimeter ECAL made of 75848 lead tungstate crystals (PbWO4, PWO) was designed in 1994 for an integrated luminosity of 500fb-1 to be achieved in 2020 [1]. In such an irradiation environment, radiation damage is mainly caused by the electromagnetic component of ionising radiation at the ECAL location in the detector. In order to study the effect of hadron originated radiation damage on a larger number of samples of PWO crystals and its impact on the performance of CMS ECAL, a dedicated program of proton irradiation in the CERN proton synchrotron (PS) facility was launched the end of 2009. A model of the proton induced damage mechanism of PWO crystal is proposed

IRRADIATION CONDITIONS AND CHARACTERISATION
RECOVERY STUDIES
Recovery with temperature
Light stimulation recovery
Combined treatment
Findings
CONCLUSION
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