Crystals for high-energy calorimeters in extreme environments

Scintillating crystals are used for calorimetry in several high-energy physics experiments. For many of them, performance has to be ensured in very difficult operating conditions, like a high radiation environment and large particle fluxes, which place constraints on response and readout time. An overview is presented of the knowledge reached up to date, and of the newest achievements in the field, with particular attention given to the performance of Lead Tungstate crystals exposed to large particle fluxes.Comment: To be published in Proc. 9th ICATPP Conference on Astroparticle, Particle, Space Physics, Detectors and Medical Physics Applications, Como, Italy, October 17th to 21st, 200

High-energy proton induced damage study of scintillation light output from PbWO4 calorimeter crystals

Eight PbWO4 crystals produced for the electromagnetic calorimeter of the CMS experiment at LHC have been irradiated in a 20 GeV/c proton beam up to fluences of 5.4 E13 p/cm2. The damage recovery in these crystals, stored in the dark at room temperature, has been followed for over a year. Comparative irradiations with 60Co photons have been performed on seven other crystals using a dose rate of 1 kGy/h. The issue whether hadrons cause a specific damage to the scintillation mechanism has been studied through light output measurements on the irradiated crystals using cosmic rays. The correlation between light output changes and light transmission changes is measured to be the same for proton-irradiated crystals and for gamma-irradiated crystals. Thus, within the precision of the measurements and for the explored range of proton fluences, no additional, hadron-specific damage to the scintillation mechanism is observed.Comment: 7 pages, 4 figure

First results on radiation damage in PbWO4 crystals exposed to a 20 GeV/c proton beam

We have exposed seven full length production quality crystals of the electromagnetic calorimeter (ECAL) of the CMS detector to a 20 GeV/c proton beam at the CERN PS accelerator. The exposure was done at fluxes of 10**12 p/cm**2/h and 10**13 p/cm**2/h and integral fluences of 10**12 p/cm**2 and 10**13 p/cm**2 were reached at both rates. The light transmission of the crystals was measured after irradiation and suitable cooling time for induced radioactivity to decrease to a safe level. First results of these measurements are shown. The possible damage mechanisms are discussed and simulations based on one possible model are presented. The implications for long-term operation of CMS are discussed and it is shown that in the whole barrel and at least most of the ECAL endcap hadron damage alone - even if cumulative - should not cause the crystals to fail the CMS specification of an induced absorption coefficient muIND < 1.5 /m during the first 10 years of LHC operation.Comment: 5 pages, to be published in Proc. ICATPP Conference on Astroparticle, Particle, Space Physics, Detectors and Medical Physics Applications (Como, Italy, 6 to 10 October 2003

Comparison between high-energy proton and charged pion induced damage in Lead Tungstate calorimeter crystals

A Lead Tungstate crystal produced for the electromagnetic calorimeter of the CMS experiment at the LHC was cut into three equal-length sections. The central one was irradiated with 290 MeV/c positive pions up to a fluence of (5.67 +- 0.46)x10^13 /cm^2, while the other two were exposed to a 24 GeV/c proton fluence of (1.17 +- 0.11) x 10^13/ cm^2. The damage recovery in these crystals, stored in the dark at room temperature, has been followed over two years. The comparison of the radiation-induced changes in light transmission for these crystals shows that damage is proportional to the star densities produced by the irradiation.Comment: 7 pages, 4 figure

Performance studies of scintillating ceramic samples exposed to ionizing radiation

Scintillating ceramics are a promising, new development for various applications in science and industry. Their application in calorimetry for particle physics experiments is expected to involve an exposure to high levels of ionizing radiation. In this paper, changes in performance have been measured for scintillating ceramic samples of different composition after exposure to penetrating ionizing radiation up to a dose of 38 kGy.Comment: 6 pages, 8 figures, to be published in the 2012 IEEE Nuclear Science Symposium Conference Recor

Studies of the effect of charged hadrons on lead tungstate crystals

Scintillating crystals are used for calorimetry in several high-energy physics experiments. For some of them, performance has to be ensured in difficult operating conditions, like a high radiation environment, very large particle fluxes and high collision rates. Results are presented here from a thorough series of measurements concerning mainly the effect of charged hadrons on lead tungstate. It is also shown how these results can be used to predict the effect on crystals due to a given flux of particles.Comment: Submitted to Proceedings Calor 2008 - XIII International Conference on Calorimetry in High Energy Physics, Pavia (Italy) 26-30 May 2008. To be published in Journal of Physics: Conference Series (8 pages, 16 figures

A FLUKA study towards predicting hadron-specific damage due to high-energy hadrons in inorganic crystals for calorimetry

Hadrons emerging from high-energy collisions, as it is the case for protons and pions at the CERN Large Hadron Collider, can produce a damage to inorganic crystals that is specific and cumulative. The mechanism is well understood as due to bulk damage from fragments caused by fission. In this paper, the existing experimental evidence for lead tungstate, LYSO and cerium fluoride is summarised, a study using FLUKA simulations is described and its results are discussed and compared to measurements. The outcome corroborates the confidence in the predictive power of such simulations applied to inorganic scintillators, which are relevant to their adoption as scintillators for calorimetry.Comment: 15 pages, 8 figure

Crystals for high-energy calorimetry in extreme environments

Crystals are used as a homogeneous calorimetric medium in many high-energy physics experiments. For some experiments, performance has to be ensured in very difficult operating conditions, like a high radiation environment, very large particle fluxes, high collision rates, placing constraints on response and readout time. An overview is presented of recent achievements in the field, with particular attention given to the performance of Lead Tungstate (PWO) crystals exposed to high particle fluxes.Comment: To be published in Proc. of the Meeting of the Division of Particles and Fields of the American Physical Society, DPF2004 (Riverside, USA, August 26th to 31st, 2004

A visualization of the damage in Lead Tungstate calorimeter crystals after exposure to high-energy hadrons

The anticipated performance of calorimeter crystals in the environment expected after the planned High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN has to be well understood, before informed decisions can be made on the need for detector upgrades. Throughout the years of running at the HL-LHC, the detectors will be exposed to considerable fluences of fast hadrons, that have been shown to cause cumulative transparency losses in Lead Tungstate scintillating crystals. In this study, we present direct evidence of the main underlying damage mechanism. Results are shown from a test that yields a direct insight into the nature of the hadron-specific damage in Lead Tungstate calorimeter crystals exposed to 24 GeV/c protons.Comment: 8 pages, 6 figure

Proof-of-principle of a new geometry for sampling calorimetry using inorganic scintillator plates

A novel geometry for a sampling calorimeter employing inorganic scintillators as an active medium is presented. To overcome the mechanical challenges of construction, an innovative light collection geometry has been pioneered, that minimises the complexity of construction. First test results are presented, demonstrating a successful signal extraction. The geometry consists of a sampling calorimeter with passive absorber layers interleaved with layers of an active medium made of inorganic scintillating crystals. Wavelength-shifting (WLS) fibres run along the four long, chamfered edges of the stack, transporting the light to photodetectors at the rear. To maximise the amount of scintillation light reaching the WLS fibres, the scintillator chamfers are depolished. It is shown herein that this concept is working for cerium fluoride (CeF$_3$) as a scintillator. Coupled to it, several different types of materials have been tested as WLS medium. In particular, materials that might be sufficiently resistant to the High-Luminosity Large Hadron Collider radiation environment, such as cerium-doped Lutetium-Yttrium Orthosilicate (LYSO) and cerium-doped quartz, are compared to conventional plastic WLS fibres. Finally, an outlook is presented on the possible optimisation of the different components, and the construction and commissioning of a full calorimeter cell prototype is presented.Comment: Submitted to Proceedings CALOR 2014, the 16th International Conference on Calorimetry in High-Energy Physics, Giessen (Germany) 6 - 11 April 2014. To be published in Journal of Physics: Conference Series (10 pages, 15 figures