Nuclear Inst. and Methods in Physics Research, A 975 (2020) 164197 Contents lists available at ScienceDirect Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima Tl concentration and its variation in a CsI(Tl) crystal for the CALIFA detector A. Knyazev a , J. Park a,j , P. Golubev a , J. Pallon a , J. Cederkall a,∗ , H. Alvarez-Pol b , J. Benlliure b , J.A. Briz c , P. Cabanelas b , E. Casarejos d , D. Cortina-Gil b , P. Díaz Fernández e , M. Feijoo b , D. Galaviz f , E. Galiana f , M.J.G. Borge c , R. Gernhäuser g , D. Gonzalez b , C. Gutierrez-Neira h , A.-L. Hartig i , A. Heinz e , B. Heiss g , H. Johansson e , P. Klenze g , T. Kröll i , T. Nilsson e , A. Perea c , L. Ponnath g , H.-B. Rhee i , J.L. Rodriguez-Sanchez b , O. Tengblad c , P. Teubig f a Department of Physics, Lund University, SE-221 00 Lund, Sweden b Dpt. de Física de Partículas, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain c Instituto de Estructura de la Materia, CSIC, E-28006 Madrid, Spain d Universidade de Vigo, E-36310 Vigo, Spain e Department of Physics, Chalmers University of Technology, S-41296 Gothenburg, Sweden f Laboratory for Instrumentation and Experimental Particle Physics, 1649-003 Lisbon, Portugal g Physik Department, Technische Universität München, 85748 Garching, Germany h Centro de Micro-Analisis de Materiales, Universidad Autonoma de Madrid, E-28049, Madrid, Spain i Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany j Center for Exotic Nuclear Studies, Institute for Basic Science (IBS), 34126 Daejeon, Korea ARTICLE INFO Keywords: Nuclear reactions Calorimeters Scintillators CsI(Tl) energy resolution ABSTRACT One of the factors that can contribute to the resolution of long, doped inorganic scintillators used for nuclear spectroscopy is the variation of the dopant concentration over the length the detector crystal. In this work an investigation of such potential variations in one of the CsI(Tl) scintillators used in the calorimeter, CALIFA, of the R 3 B experiment at FAIR, has been performed using particle induced X-ray emission. No statistically significant gradient in doping level was found along the long axis of the investigated sample crystal and the mean value of the Tl concentration was measured to be 0.0839(38)% by weight. This corresponds to a light output of 97.3 +1.3 −1.7 % relative to the maximum attainable light output according to previously published work. By taking the ±1 bounds, the 3% statistical spread in the relative light output provides a good reference value of the minimum light-output non-uniformity observed for the CALIFA crystals. If the relative light output is estimated pointwise from a set of Tl concentration measurements a light-output non-uniformity of 4.6(2.4)% results. For a  -ray energy of 662 keV the deduced variation in Tl concentration contributes with 0.48(6)% to the typical resolution of 7.74(6)% measured with a collimated source along the crystal main axis. The result is of interest for the characterization of the detector system performance and for realistic simulations of the light collection process in detector systems that are used for nuclear spectroscopy and calorimetry. 1. Introduction 1.1. Purpose of the study In order to properly characterize the performance of a multidetector system that uses scintillation as detection mechanism for spectroscopic measurements, several different effects need to be considered. Specif- ically, for a case where long frustum-shaped detector elements are used, light collection from different parts of the detector volume will be influenced both by absorption of the scintillation light, and by its reflection at the boundaries of the detector volume [1,2]. This problem becomes particularly interesting for a case where high-energy  -rays ∗ Corresponding author. E-mail address: joakim.cederkall@nuclear.lu.se (J. Cederkall). and charged particles from a nuclear reaction are to be detected using the same detector system since measurement of the energy carried by one photon or charged particle often requires summing of signals from several detector elements. If significant non-uniformity in light output exists between the different parts of the detector volume it will translate into a loss of overall resolution. We, as well as other authors, have addressed light absorption and reflective properties for detectors built on scintillator elements in previ- ous work [1–4] and also discussed how one can minimize its influence on the detector response. However, one effect where more detailed information would be beneficial, e.g. for detector simulations, is the https://doi.org/10.1016/j.nima.2020.164197 Received 21 February 2020; Received in revised form 25 May 2020; Accepted 27 May 2020 Available online 29 May 2020 0168-9002/© 2020 Published by Elsevier B.V.