Radiation Measurements 129 (2019) 106201 Available online 9 October 2019 1350-4487/© 2019 Elsevier Ltd. All rights reserved. A method of testing the uniformity of planar radioactive α and β sources used in luminescence readers Jacek Pawlyta * , Konrad Tudyka, Andrzej Bluszcz, Grzegorz Adamiec Institute of Physics – Centre of Science and Education, Silesian University of Technology, Gliwice, Poland, ul. Konarskiego 22B, 44-100, Gliwice, Poland A R T I C L E INFO Keywords: Radioactive planar sources Homogeneity Uniformity Luminescence dating Radiation dose Am-241 Sr-90/Y-90 ABSTRACT In this work we describe a simple method for assessing the non-uniformity of planar α and β radioactive sources. In this method we put in contact the radioactive source with the scintillator. This causes a weak light to be emitted by the scintillator. Applying a CCD light matrix we take image sequences and process them with methods developed in astronomy for observing weak light emitters. Using this method, we investigate two β and two α sources dedicated to estimating the radiation dose absorbed in trapped charge dating. In this application radioactive source non-uniformity has signifcant practical impli- cations. The applied method shows that one of the β sources and one of the α sources are non-uniform. 1. Introduction Planar radioactive β and α sources are used in estimating the radia- tion dose absorbed by minerals or artifcial dosimeters by means of trapped charge methods (e.g. optically stimulated luminescence – OSL, thermoluminescence – TL, electron spin resonance – ESR, etc.). In these methods, grains or dosimeters are usually placed on metal discs and the irradiation by the planar source is used to calibrate the investigated material, i.e. to determine the relationship between the used signal and the absorbed dose, the so-called growth curve. It is important that during the growth curve building, all grains receive the same dose (see e. g. Fuchs and Lomax, 2018). In the case of multigrain aliquots, when the dose response is nonlinear and measurements of the total signal stem- ming from an assemblage of non-uniformly irradiated grains result in additional effects that are diffcult to account for. On the other hand, when single grain OSL is measured, the dose rate variation across the sample holder results in an additional scatter of obtained absorbed dose estimates. In practice, it is assumed that the radioactive material is distributed uniformly over the surface of the source. It is very chal- lenging to determine the uniformity of sources of high activity (in the range of GBq for beta sources and hundreds of MBq for alpha sources as used in trapped charge dating). A few works have been devoted to testing the uniformity of radiation sources. Spooner and Allsop (2000) attempted to establish the unifor- mity of the radiation feld produced by a 90 Sr/ 90 Y source at the position of the irradiated sample. They used a small CaF 2 chip attached to an optical fbre. The chip was moved under the source using an X–Y stage and the emitted radioluminescence indicated the intensity of beta ra- diation. A different approach was taken by Richter et al. (2012) who used a radiochromic flm to see the dose rate at the sample position to test the uniformity of a new source design. Lee et al. (2018) used EBT flms to get information about dose distribution from 241 Am sources. Direct measurements of beta dose absorbed by quartz grains placed on a sample holder were undertaken by Ballarini et al. (2006) and Veronese et al. (2007). This method required the availability of a single grain attachment and a quartz sample in which the majority of grains display high sensitivity. In this work we present an alternative simple yet fast and effective method for examination of the source uniformity. 2. Methods 2.1. Radioactive sources The uniformity of the radioactive surface of two 90 Sr/ 90 Y β sources of the same type was tested. The nominal radioactivity of both radioactive sources was 2.8 GBq. Radioactive material in those sources is enclosed in a stainless-steel capsule VZ-2518-001 with a diameter of 9.5 mm and 6.5 mm height. The diameter of the radioactive area is 4.95 mm and it is protected with a 0.025 mm thick window. The sources were obtained from Eckert & Ziegler Nuclitecd. For alpha radiation, the uniformity of two different 241 Am sources * Corresponding author. E-mail address: jacek.pawlyta@polsl.pl (J. Pawlyta). Contents lists available at ScienceDirect Radiation Measurements journal homepage: http://www.elsevier.com/locate/radmeas https://doi.org/10.1016/j.radmeas.2019.106201 Received 18 March 2019; Received in revised form 24 September 2019; Accepted 4 October 2019