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Further physical programs at the LHC will require a significant increase of the accelerator luminosity throughout the High Luminosity phase of LHC [1]. During this period, charged hadrons and neutrons with fluences higher than 1014 p/cm2 per year in the largest pseudo-rapidity regions of the detectors will have a non-negligible influence on the radiation damage of materials. Moreover, with the increasing activation of the experimental equipment, it will become more difficult to periodically replace and maintain the detector components. Therefore, the selection of materials for new detectors to be used at the upgrade of experimental setup requires a more reliable assessment of the risks of detector failures due to severe radiation damage. Thus, detecting materials not only for electromagnetic calorimeters, but also for hadron calorimeters have to show tolerance to a strong irradiation background of proton collider experiments.
During last few years it was shown that Y3Al5O12:Ce (YAG:Ce) crystal has a very low optical transmission damage after irradiation with 24 GeV protons up to a fluence of 5x1014 p/cm2. It was shown that the presence of Ce3+ ions in the crystal prevents the appearance of color centers in the visible range. Good radiation hardness of YAG:Ce crystals to γ irradiation and 150 MeV protons also was confirmed [2,3]. Ce doped garnets have several additional advantages: their luminescence is shifted to the green-yellow spectral range which well matches the spectral sensitivity of silicon photomultipliers (SiPMs); garnet structure allows a variety of physical possibilities to engineer scintillation properties of materials based on it, particularly – scintillation kinetics and a scintillation spectrum maximum wavelength.
However, production of YAG:Ce in a single crystalline form is costly because crystal growth is performed at temperature near 1900 °C with a very low rate of transformation of a raw material into a crystal. As an alternative solution to the single crystalline option we propose YAG:Ce based polycrystalline scintillation materials, obtained by cheaper chemical routes. We have prepared and tested two variants: 1) a composite material, composed of large sized grains, packed and glued together into a translucent body with density up to 50% of the single crystal; 2) sintered translucent ceramic body with density ~98% of the theoretical density. Starting YAG:Ce powders for both approaches are prepared using a classical co-precipitation method. This approach allows producing large volumes of relatively cheap high quality polycrystalline material. Then powders undergo different mechanical and thermal treatment to form a material.
Different proposed prototypes of the detecting modules are given in Figure 1. As all components of composite modules are selected to be radiation hard, such technology can be considered a suitable option to replace plastic scintillators in a region of a detector where high radiation hardness is mandatory.
In this study, we report the results of a comparative tests of the YAG:Ce single crystals and composite modules obtained by different approaches. Light yield, obtained for some samples of such polycrystalline materials, was up to 40-60% higher then for single crystals, with kinetics not worse then for single crystals.
ACKNOWLEDGEMENTS
Work was supported by Ministry of Science and Education of Russian Federation, subsidy agreement № 14.625.21.0033 dated 27.10.2015, project identifier RFMEFI62515X0033.
REFERENCES
- The CERN Large Hadron Collider: Accelerator and Experiments, Vol. 1-2, CERN, Geneva, 2009
- K.-T. Brinkman, A. Borisevich, V. Dormenev, V. Kalinov, M. Korjik et al., “Radiation damage and Recovery of medium heavy and light inorganic Crustalline, Glass and Glass Ceramic materials after Irradiation with 150 MeV protons and 1.2 MeV gamma-rays”, presented at IEEE 2014 IEEE Nuclear Science Symposium and Medical Imaging Conference, October 2014, USA.
- M.T. Lucchini, K. Pauwels, K. Blazek, S. Ochesanu, E. Auffray, “Radiation Tolerance of LuAG:Ce and YAG:Ce Crystals Under High Levels of Gamma-and Proton-Irradiation”, IEEE Transactions on Nuclear Science, 63(2), 2016, 586-590.
