Elemental quantification of large gunshot residues A. Duarte a,b , L.M. Silva a,b,c , C.T. de Souza a , E.M. Stori a , L.A. Boufleur a,b , L. Amaral a , J.F. Dias a,b,⇑ a Ion Implantation Laboratory, Institute of Physics, Federal University of Rio Grande do Sul, Av. Bento Gonçalves 9500, P.O. Box 15051, CEP 91501-970 Porto Alegre, RS, Brazil b Graduate Program on Materials Science, Federal University of Rio Grande do Sul, Av. Bento Gonçalves 9500, CEP 91540-000 Porto Alegre, RS, Brazil c Forensic Institute of Porto Alegre, Av. Princesa Isabel 1056, CEP 90230-010 Porto Alegre, RS, Brazil article info Article history: Received 22 July 2014 Received in revised form 21 November 2014 Accepted 24 November 2014 Available online 12 January 2015 Keywords: Gunshot residues PIXE Micro-PIXE abstract In the present work we embarked on the evaluation of the Sb/Pb, Ba/Pb and Sb/Ba elemental ratios found in relatively large particles (of the order of 50–150 lm across) ejected in the forward direction when a gun is fired. These particles are commonly referred to as gunshot residues (GSR). The aim of this work is to compare the elemental ratios of the GSR with those found in the primer of pristine cartridges in order to check for possible correlations. To that end, the elemental concentration of gunshot residues and the respective ammunition were investigated through PIXE (Particle-Induced X-ray Emission) and micro-PIXE techniques. The ammunition consisted of a .38 SPL caliber (ogival lead type) charged in a Tau- rus revolver. Pristine cartridges were taken apart for the PIXE measurements. The shooting sessions were carried out in a restricted area at the Forensic Institute at Porto Alegre. Residues ejected at forward direc- tions were collected on a microporous tape. The PIXE experiments were carried out employing 2.0 MeV proton beams with a beam spot size of 1 mm 2 . For the micro-PIXE experiments, the samples were irra- diated with 2.2 MeV proton beams of 2 Â 2 lm 2 . The results found for the ratios of Sb/Pb, Ba/Pb and Sb/Ba do not correlate with those stemming from the analysis of the primer. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Gunshot residues (GSR) constitute a relatively easy way to iden- tify an event where a firearm was discharged. Usually, GSR are deposited in the vicinity where the firing event took place includ- ing surfaces, objects and the bodies of the shooter and the victim. Such particles are commonly of spherical shape with a diameter of few micrometers and are characterized by a mixture of elements present in the primer, projectile, gun powder, case and projectile. In particular, the primer plays an important role since it contains barium nitrate, antimony sulfide and lead styphnate [1], which are considered the fingerprints of such particles [2]. Despite several techniques like Neutron Activation Analysis (NAA) and Atomic Absorption Spectroscopy have been used to characterize GSR, the most popular one is the Scanning Electron Microscopy coupled with an Energy Dispersive Spectrometer (SEM–EDS) [3]. The systematic use of SEM–EDS systems in forensic sciences dates back to the seventies [4] and ever since it became the most powerful technique accepted in court for the analysis of GSR [5]. Around the same time, Particle-Induced X-ray Emission (PIXE) begins to be explored as a potential technique for use in forensic sciences [6,7]. However, the use of broad beam to analyze GSR proved to be a drawback when compared to SEM results. With the advent of the scanning microprobe capability together with better X-ray spectrometers brought new impetus to ion- based techniques applied to forensic sciences. Although l-PIXE and SEM–EDS can be used as complementary techniques [8], fea- tures like sensitivity, bulk analysis capability and non-destructive character make PIXE and other ion beam techniques like l-PIXE, Elastic Backscattering Spectrometry (EBS) and Nuclear Reaction Analysis (NRA) powerful tools for GSR analysis. In general, basic techniques like l-PIXE and EBS have a potential use in the analysis of GSR [2,9], while several other ion-based techniques can be employed for a full assessment of the case under study [5]. Despite a huge volume of work dedicated to the study of GSR, little attention has been given to the study of relatively large par- ticles ejected during the discharge of a firearm. Usually, the focus is laid on particles deposited in the hands or clothes of someone who discharged a firearm. In this case, relatively small particles are the most likely to remain in such places since large ones are easier to be removed by several processes. On the other hand, relatively large particles may be thrown on the floor or just stick to a nearby wall. Despite these particles cannot be used to incriminate some- body, they could act as supporting evidence in a crime scene. In http://dx.doi.org/10.1016/j.nimb.2014.11.116 0168-583X/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Institute of Physics, UFRGS, Brazil. Tel.: +55 51 3308 7248. E-mail address: jfdias@if.ufrgs.br (J.F. Dias). Nuclear Instruments and Methods in Physics Research B 348 (2015) 170–173 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb