Radiation damage measurements of undoped lead tungstate crystals for the CMS electromagnetic calorimeter at LHC

Crystals for High-Energy Physics Calorimeters in Extreme Environments

“…The correlation in Fig. 2(a), between µ IN D (420 nm) and fluence, is consistent with a linear behaviour over two or- ders of magnitude, showing that proton-induced damage in PbWO 4 is predominantly cumulative, unlike γ-induced damage, which reaches equilibrium [1,4]. Figure 2(b) shows µ IN D (420 nm) plotted versus light wavelength for the proton-irradiated crystal a" and for the two γ -irradiated crystals v and y.…”

“…Phosphorescence or afterglow appear sometimes [2], which increase the noise levels in the detected light signal, possibly worsening the energy resolution (in a negligible way for PbWO 4 in LHC experiments [3]), while the scintillation mechanism is generally not damaged. Recovery of damage at room temperature can occur depending on crystal type and growth parameters, giving rise to a dose-rate dependence of damage equilibrium levels [1,4] and to a recovery speed dependent on the depth of traps. That ionising radiation only affects LT, means the damage can be monitored through light injection and corrected for, as it is done in the CMS Electromagnetic Calorimeter (ECAL) [5].…”

Evolution Studies of the CMS Electromagnetic Calorimeter Endcap Signals

“…We do not use the maximal change in VPT/PN, but define First, we test if the correlation between (VPT/PN) and μ std is observed over a large span of time. We define the correlation coefficient 5) where i denotes the ith crystal within n crystals contributing to the correlation. The values within are the averaged values for all n crystals.…”

The CMS Ecal Project – Overview and Status Report

“…It is thus possible to monitor the loss in transmission due to irradiation using a light injection system in the calorimeter, and to apply corrections for it. Extensive R&D work has been carried out to improve the crystal radiation hardness through the optimisation of raw materials purity, of stoichiometry, through doping and post-growth treatments in gaseous atmospheres (so-called annealing) [8].…”

“…The efforts were concentrated there as well on all aspects of crystal growth, where progress was aimed at in steps, with the successful production of 5 cm long, extremely radiation hard crystals [8], progressing then to 10 cm long radiation resistant samples [9] and now working on full-size crystals. In parallel, SIC is preparing the infrastructure for mass production, through the development of multiple crystal furnaces, where 10-crystal furnaces are already operational and two 28-crystal furnaces are being constructed, along with cutting and polishing machines.…”