Nuclear Instruments and Methods in Physics Research A 569 (2006) 355–358 Evaluating the radiation detection of the RbGd 2 Br 7 :Ce scintillator by Monte Carlo methods Panagiotis Liaparinos a , Ioannis Kandarakis b , Dionisis Cavouras b , Harry Delis a , George Panayiotakis a,Ã a Department of Medical Physics, Medical School, University of Patras, Patras 265 00, Greece b Department of Medical Instruments Technology, Technological Educational Institution of Athens, Ag. Spyridonos Street, Aigaleo, Athens 122 10, Greece Available online 8 September 2006 Abstract The purpose of this study was to investigate the radiation detection efficiency of the recently introduced RbGd 2 Br 7 :Ce (RGB) scintillator material by a custom developed Monte Carlo simulation code. Considering its fast principal decay constant (45 ns) and its high light yield (56 000 photons/MeV), RbGd 2 Br 7 :Ce appears to be a quite promising scintillator for applications in nuclear medical imaging systems. In this work, gamma-ray interactions, within the scintillator mass were studied. In addition, the effect of K- characteristic fluorescence radiation emission, re-absorption or escape, as well as the effect of scattering events on the spatial distribution of absorbed energy was examined. Various scintillator crystal thicknesses (5–25 mm), used in positron emission imaging, were considered to be irradiated by 511 keV photons. Similar simulations were performed on the well known Lu 2 SiO 5 :Ce (LSO) scintillator for comparison purposes. Simulation results allowed the determination of the quantum detection efficiency as well as the fraction of the energy absorbed due to the K-characteristic radiation. Results were obtained as a function of scintillator crystal thickness. The Lu 2 SiO 5 :Ce scintillator material showed to exhibit better radiation absorption properties in comparison with RbGd 2 Br 7 :Ce. However, RGB showed to be less affected by the production of K-characteristic radiation. Taking into account its very short decay time and its high light yield, this material could be considered to be employed in positron imaging (PET) detectors. r 2006 Elsevier B.V. All rights reserved. PACS: 02.50.N; 29.40.M Keywords: Scintillators; Monte Carlo; PET radiation detectors 1. Introduction In positron emission tomography (PET) medical ima- ging systems, photon detection and counting is achieved via scintillator based radiation detectors [1–4]. Properties of primary importance to be taken into account in developing new scintillator materials are the following: photon detection efficiency, high light yield, fast response, linearity, minimal afterglow, easy growth and low cost [3,4]. Many of the commercially available scintillators, e.g. BGO, LSO and GSO, combine some of the aforemen- tioned requirements [3–6]. However, BGO is a relatively slow scintillator (300 ns), with high refractive index, which increases light reflection at the crystal-photomultiplier interface. A large amount of light produced within the crystal, cannot be captured by the photomultipliers. LSO is a scintillator of high cost, which, in addition, exhibits intrinsic radioactivity due to the presence of lutetium-176 (2.6%). In PET scanners this radioactivity, may increase background counts. Finally, GSO is a scintillator of comparatively lower effective atomic number and lower light output [5–8]. Since, the demand for new improved PET detectors increases rapidly, further investigation towards developing new luminescent materials with better scintillating perfor- mance is required. RbGd 2 Br 7 :Ce (RGB) is a recently introduced cerium doped scintillator. A number of published studies have focused on the performance of this scintillator, evaluating its physical properties, its ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2006.08.037 Ã Corresponding author. Tel./fax: +30 61 996113. E-mail address: panayiot@upatras.gr (G. Panayiotakis).