IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 61, NO. 1, FEBRUARY 2014 501 Comparison of Radiation Damage Effects in PWO Crystals Under 150 MeV and 24 GeV High Fluence Proton Irradiation Valera Dormenev, Mikhail Korjik, Till Kuske, Vitaly Mechinski, and Rainer W. Novotny, Member, IEEE Abstract—Radiation damage effects induced by the hadronic part of ionizing radiation in experiments at high-energy and high-luminosity accelerators will play a significant role as limiting factor of the long term stability when operating an experimental setup. Measurements of the deterioration of the optical transmis- sion of lead tungstate (PbWO , PWO) scintillation crystals were performed after irradiation with high and low energy protons. One sample with CMS specification was irradiated in 2010 with a 24 GeV/c proton beam at the CERN Proton Synchrotron (PS) with a flux of about p/(cm s) up to an accumulated fluence of p/cm . Eight more crystals of PWO-II quality with dimensions of cm were selected from the set of crystals produced for the PANDA electromagnetic calorimeter at the future FAIR facility at Darmstadt. Four crystals were produced by the Bogoroditsk Technical Chemical Plant (Russia) and the others by the Shanghai Institute of Ceramics (China). These sam- ples were irradiated in 2012 with a 150 MeV proton beam at the AGOR accelerator at KVI (Groningen, The Netherlands) with a flux of up to an integral fluence of about p/cm and p/cm , respectively. Due to the proton induced activation of long-lived radioactive secondaries the optical inspection of all samples had to be performed several months after irradiation for safety reasons. However, the samples were kept continuously cold to minimize thermal recovery. Both irradiations produced a similar set of induced absorption bands. Moreover, a shift of the fundamental absorption edge at short wavelength appears even after irradiation with low energy protons. The contribution will show in detail the set of experimental data and discuss a possible mechanism for an understanding and interpretation of the observed effects. Index Terms—Calorimetry, lead tungstate, radiation detectors, radiation effects, scintillator. I. INTRODUCTION T HE PANDA detector is a new detector system which will be installed at the international FAIR accelerator facility (Darmstadt, Germany) with a wide research program [1], [2]. Manuscript received May 17, 2013; revised July 19, 2013; accepted July 26, 2013. Date of publication September 04, 2013; date of current version February 06, 2014. This work was supported in part by BMBF, in part by GSI, in part by HIC4FAIR, and in part by the European Commission within the 7th Framework Program through IA-ENSAR (contract Nr. RII3-CT-2010-262010). V. Dormenev, T. Kuske, and R. W. Novotny are with the 2nd Physics Institute, Justus-Liebig-University, D-35392 Giessen, Germany (e-mail: valery.dormenev@exp2.physik.uni-giessen.de; till.kuske@exp2.physik.uni- giessen.de; rainer.novotny@exp2.physik.uni-giessen.de). M. Korjik and V. Mechinski are with the Institute for Nuclear Problems, 220030, Minsk, Belarus (e-mail: mikhail.korjik@cern.ch; lupus@belastro.net). Digital Object Identifier 10.1109/TNS.2013.2275901 One of the major detector components will be the Electromag- netic Calorimeter (EMC) in the target region based on a new generation of lead tungstate crystals PbWO (PWO-II) [3], [4]. The first generation of mass produced PWO-I crystal is used for the electromagnetic calorimeter section ECAL of CMS at LHC. The growing technology of CMS type crystals was optimized to obtain detector units with high radiation hardness and less strin- gent requirements to light yield [5], [6]. In contrast, the production technology of PWO-II crystals for the PANDA EMC was focused to increase the light yield without degradation of radiation hardness [7], [8]. A further increase can be obtained by additional cooling down to low tem- peratures exploiting the reduction of luminescence quenching. The temperature gradient of the light yield of PANDA PWO-II crystal is C in the temperature range from C till C. The operating temperature of the PANDA EMC was chosen as C. At that temperature the light yield reaches a 3.5 times higher value relative to room temperature without significant contributions of slow components. As a result of the optimization of PWO-II crystal properties the PANDA calorimeter can detect photons in an energy range from 15 GeV down to 10–20 MeV, respectively. Crystals for the CMS and partly for the PANDA calorime- ters were produced by Czochralski method at the Bogoroditsk Technological Chemical Plant (BTCP, Bogoroditsk, Russia). An alternative producer for mass production of PWO crystals is Shanghai Institute of Ceramics, Chinese Academy of Science (SICCAS, Shanghai, China) applying the modified Bridgman method [9]. The radiation damage of PWO under electromagnetic irradi- ation has been well studied [10], [11]. It was concluded, there is no damage of the host structure and the luminescence mech- anism of PWO crystals in the strong electromagnetic environ- ment. Detailed investigations of radiation damage of PWO crystals under hadron irradiation were done in the last years [12]–[14] focusing on high particle fluxes. Recent results of such kind of damage in both types (BTCP and SICCAS) of PWO crystal are presented in this paper studied at much lower particle energies. II. RADIATION DAMAGE AND STIMULATED RECOVERY PROCESSES IN PWO CRYSTALS A. Gamma-Irradiation Damage The main mechanism of the radiation damage in PWO is degradation of optical transmittance under ionizing radiation. 0018-9499 © 2013 IEEE. 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