Radiation damage mechanisms in CsI(Tl) studied by ion beam induced luminescence Alberto Quaranta a,b, * , Fabiana Gramegna b , Vladimir Kravchuk b , Carlo Scian a,b a Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali – DIMTI, Universita ` di Trento, Via Mesiano 77, I-38050 Povo, Trento, Italy b Laboratori Nazionali di Legnaro – INFN, Via dell’Universita ` 2, I-35020 Legnaro, Padova, Italy Available online 28 March 2008 Abstract Ion beam induced luminescence (IBIL) has been used to study the kinetics of defect production under ion beam irradiation in CsI(Tl) crystals with different Tl + concentrations (250, 560, 3250 and 6500 ppm). The crystals have been irradiated with H + and 4 He + at 1.8 MeV. Both the scintillator spectra after irradiation and the intensity decrease at different wavelengths as a function of the fluence have been measured. The emission bands shift to higher wavelengths after irradiation, and the light decrease has been interpolated fol- lowing a saturation model for the point defect concentration. Crystals with low Tl + concentrations present the UV emission peak of pure CsI at 300 nm whose intensity during H + irradiation and reaches a maximum under He + irradiation. At low Tl + concentrations the dam- age rate depends on the ion stopping power, while at higher concentrations it depends on the activator concentration. The results can be interpreted by assuming that the defects affecting the light emission are point defects nearby Tl + ions. Ó 2008 Elsevier B.V. All rights reserved. PACS: 78.60.Hk; 61.80.x; 61.72.Ji Keywords: Ion beam induced luminescence; CsI; Damage rate 1. Introduction CsI(Tl) scintillators are widely used in nuclear and high energy physics experiments due to their high light output, good mechanical stability and to the possibility to grow large crystals with a small amount of imperfections. More- over, it is well known that both light output [1,2] and pulse shape [3,4] of CsI(Tl) crystals depend not only on the deposited energy but also on the atomic number and mass of the incident ion. In the past CsI(T1) had been largely studied for the detection of ionizing radiation, in particular for ions and fission products [5]. However the mismatch of the CsI(T1) scintillation emission spectrum to the spectral sensitivity of photomultipliers, together with the rising application of semiconductor detectors, prevented for a while a widespread use of this crystal as a scintillation detector. In a following period, the development of large area silicon photodiodes, whose quantum efficiency was properly matching the CsI(Tl) spectrum, strongly stimu- lated the use of this crystal in nuclear physics experiments, in particular for the production of large arrays of detectors [4,6]. For these reasons a great deal of work has been carried out during these last years to study the energy transfer mechanisms involved in the scintillation process [2,7] and the dependence of the scintillation yield on the Tl + concen- tration [8,9]. In fact, a deeper knowledge of these processes could simplify the time consuming calibration procedures which are necessary for the setting of detector arrays con- stituted by several tens of CsI(Tl) crystals. The scintillation spectrum of CsI(Tl) is constituted by a broad band at about 550 nm coming from the recombination 0168-583X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2008.03.195 * Corresponding author. Address: Dipartimento di Ingegneria dei Materiali e delle Tecnologie Industriali – DIMTI, Universita ` di Trento, Via Mesiano 77, I-38050 Povo, Trento, Italy. Tel.: +39 0461882450; fax: +39 0461881945. E-mail address: quaranta@ing.unitn.it (A. Quaranta). www.elsevier.com/locate/nimb Available online at www.sciencedirect.com Nuclear Instruments and Methods in Physics Research B 266 (2008) 2723–2728 NIM B Beam Interactions with Materials & Atoms