Coincidence summing corrections for volume samples using the PENELOPE/penEasy Monte Carlo code A. Vargas n , A. Camp, I. Serrano, M.A. Duch Institute of Energy Technologies (INTE)—Technical University of Catalonia (UPC), Av. Diagonal 647, 08028 Barcelona, Spain HIGHLIGHTS  Computation of coincidence summing corrections for peaks of 152 Eu and 134 Cs.  The MC penEasy code has been modified to include the coincidence summing effect.  The correction factors have been obtained with PENELOPE/penEasy MC code.  Results have been validated using an ICRM intercomparison. article info Available online 27 November 2013 Keywords: Coincidence summing Gamma-ray spectrometry Volume sources Monte-Carlo simulation X-rays abstract The coincidence summing correction factors estimated with penEasy, a steering program for the Monte Carlo simulation code PENELOPE, and with penEasy-eXtended, an in-house modified version of penEasy, are presented and discussed for 152 Eu and 134 Cs in volume sources. The geometries and experimental data were obtained from an intercomparison study organized by the International Committee for Radionuclide Metrology (ICRM). A significant improvement in the results calculated with PENELOPE/ penEasy was obtained when X-rays are included in the 152 Eu simulations. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Coincidence summing in gamma-ray spectrometry is a problem that has been extensively studied in recent decades. Different works with full Monte Carlo (MC) simulations (García-Talavera et al., 2001; Décombaz et al., 1992) and with analytical computa- tions of the joint emission probabilities (Sima and Arnold, 2008; Vidmar et al., 2011), have been carried out in order to obtain the coincidence summing correction factors for radionuclides which emit two or more photons in cascade. Monte Carlo simulations can describe very complex situations analyzing each interaction of the particle history, step-by-step, so they are not limited by equation complexity as the analytical computations are. On the other hand there is a statistical spread associated with Monte Carlo simula- tions which can be a problem for gamma-rays with low emission probabilities, thus in this case a large number of decays must be processed. In the intercomparison carried out by the Gamma Ray Spectrometry Working Group of the International Committee for Radionuclide Metrology (ICRM) for volume sources in close geometries (Lépy et al., 2012), only one out of 16 participating laboratories reported results obtained by full MC. In this work, we have developed PENELOPE/penEasy-eXtended, an in-house modified version of penEasy, a main program for the Monte Carlo code PENELOPE (Salvat et al., 2009). The code has been modified in order to take into account coincidence summing and it is used to estimate the corresponding corrective factors for 152 Eu and 134 Cs. As pointed out in Lépy et al. (2012), if the X-rays for 152 Eu are not included in the code the correction can be biased. Therefore, the X-rays from electron capture (EC) of 152 Eu have been included in PENELOPE/penEasy-eXtended code in order to analyze their significance. This code has been evaluated using the results from the ICRM intercomparison campaign. 2. Methods PENELOPE (Salvat et al., 2009) is a full Monte Carlo code for simulation of coupled electron–photon transport in arbitrary materials for a wide energy range, from a few hundreds electron volts to about 1 GeV. The core of the program is a set of Fortran subroutines together with a general-purpose main program. Some examples of main programs are supplied with the distribution package. In this work, penEasy version 2009 has been used. It provides users with a set of source models, tallies and variance reduction techniques that are invoked from a structured code. Although users need only to input the required information Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes 0969-8043/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apradiso.2013.11.057 n Corresponding author. Tel.: þ34 93 401 08 99. E-mail address: arturo.vargas@upc.edu (A. Vargas). Applied Radiation and Isotopes 87 (2014) 376–379