J Forensic Sci, 2015 doi: 10.1111/1556-4029.12785 Available online at: onlinelibrary.wiley.com
TECHNICAL NOTE CRIMINALISTICS
Ilker Kara,1,2 Ph.D.; Sefer Bora Lisesivdin,2 Ph.D.; Mehmet Kasap,3 Ph.D.; Elif Er,3 PG.Dip.; and Ugur Uzek,3 B.Sc.
The Relationship Between the Surface Morphology and Chemical Composition of Gunshot Residue Particles
ABSTRACT: In this study, chemical composition and morphology of gunshot residue (GSR) of 9 9 19 mm Parabellum-type MKE (Turkey)-brand ammunition were analyzed by scanning electron microscope and energy dispersive X-ray spectrometer. GSR samples were collected by “swab” technique from the shooter’s right hand immediately after shooting. According to general principles of thermodynamics, it is likely that the structures will have a more regular (homogeneous) spherical form to minimize their surface area due to very high temperatures and pressures that occur during explosion. Studied samples were collected under the same conditions with the same original ammunition, from the same firearm and a single shooter. This is because many other variables may affect size, structure, and composition in addition to the concentrations of elements of the structure. Results indicated that the chemical compositions are effective in the formation of GSR morphological structures. KEYWORDS: forensic science, firearms examination, gunshot residues, primer mixtures, SEM-EDS examination
Gunshot residues are formed as a result of a highly exothermic process in gas, liquid, or solid form when a reaction takes place under high temperature and pressure. The condensed reaction products are accumulated on the shooter’s skin, clothes, or firearm in a partly solidified GSR form. GSR usually has a distinct morphology and composition and consists of burnt and unburnt mostly spheroidal particles of 1.1–50 lm (sometimes larger) in diameter (1). As GSR consists of inorganic substances, it can be analyzed by various methods. Contents of the compounds, quantities, and sizes of a large number of particles can be analyzed visually in a fast and practical manner (manually or automatically), thanks to SEM/EDS (2,3). The elemental content of the particles can be classified by this method (4–8). Experimental studies are intended to identify rare elements, such as lead, barium, and antimony in the primer residues of ammunition (9). It is possible for the reaction products to be more homogeneous (but not necessarily) as pressure, temperature, and vaporization are higher than the surrounding atmosphere during explosion (10). As a result, the structures formed under these conditions tend to be smaller, more spherical, and homogeneous in terms of compound distribution. There is no systematic approach to analyze the relationship between morphological structures, basic components, and amounts of the component in 1
Department of Criminal Police Laboratories, Turkish National Police, 06830 Golbasi, Ankara, Turkey. 2 Department of Physics, Gazi University, 06500 Teknikokullar, Ankara, Turkey. 3 Department of Chemistry, Ankara Criminal Police Laboratory, 06830 Golbasi, Ankara, Turkey. Received 19 Mar. 2014; and in revised form 13 Aug. 2014; accepted 15 Aug. 2014. © 2015 American Academy of Forensic Sciences
these residues formed. If there is a relationship between concentrations and types of the compounds of morphological structures of GSR, then it should be possible to draw conclusions about the formation conditions of GSR. According to general thermodynamic principles, there may be a relationship between components, morphologies, and conditions (i.e., level of confinement) of these residues.
Materials and Methods The subject of the study is the GSR collected by swab technique from the shooter’s hand after firing shots into a water tank. This test was carried out by a single shooter. Three shots were fired with each ammunition type. The samples were collected on aluminum stubs immediately after each shot by a double-sided adhesive tape from the shooter’s right hand. GSR was collected by pressing the stub 100 times to the hand skin including thumb and index finger of the right hand. To prevent any accidental contamination, no other shooter collected samples. For the same reason, the residues were collected from only one person and analyzed with the same strict conditions. This experimental study was carried out at The Directorate Department of the Ankara Criminal Police Laboratory (in Turkish: KPL). All of the tests were carried out in the KPL shooting room. In test shooting, we used a Sarsilmaz brand Mega 2000 Kilinc model semi-automatic 9 mm Parabellum pistol [Machine Chemistry Institute (MKE)] with a 2010 gun cartridge. In the experiment, the barrel of the weapon was cleaned before every shooting. The cleaning process began with mechanical cleaning. Then, the barrel was washed in deionized water in an ultrasonic bath. Lastly, the barrel was dried with dry nitrogen 1
2
JOURNAL OF FORENSIC SCIENCES
gas. This process was performed more than once due to the barrel’s state. The samples were examined with the use of a JEOL/ JSM-6400 scanning electron microscope (SEM), Jeol, Japan. Acceleration voltage was 20 KV, tilt of sample was 0°, and working distance was 39 mm. Images observed were secondary electron images coupled with an INCA energy X-ray spectrometer (Oxford Instruments Ltd., Houston, TX). All analyses were taken from the highest, flattest point on each sample. For the spheres or spheroids, the approximate centers of the structures were chosen. There was a large diversity in the observed particle sizes. However, similarly sized particles were used in the quantitative analyses. As seen from Fig. 1, the 9 9 19 mm Parabellum is the most common handgun caliber among civilians and criminals in Turkey (personal communication). This caliber was selected, and all of the tests in this experimental study were performed with a Parabellum 9 9 19 mm calibre Model 2000 Kilinc Sarsilmazbrand semi-automatic handgun. To provide more reliable results, the test fires were performed using the same brand, in the same year, and with the same ammunition lot (MKEK-2010/3). Using the same brand, year, and ammunition lot reduced the number of variables and prevented the emergence of differences in the primer and gunpowder composition. The common primer composition of a 9 9 19 mm calibre MKEK-brand cartridge was 38% lead styphnate (TNR Pb), 6% tetracene (TRZN), 34% barium nitrate Ba {NO3}, 15% antimony sulfide Sb2S3, 4% pentrite (PETN), and 3% aluminum powder (11). To prevent contamination, the barrel and breech face were cleaned by a three-step cleaning process before every shoot set. The first step of cleaning was mechanical cleaning with a guncleaning brush. A new cleaning brush was used for each shoot set. In the second step, the barrel was washed with deionized water in an ultrasonic bath. In the last step, the barrel was dried with dry nitrogen gas. Results and Discussion Gunshot residues are spherical particles and can be divided into three groups according to their surface structures (Table 1):
regular spheres, spheroids, and irregular spheres. Spheroids are formed by the combination of small spheres with regular surfaces, and irregular spheres are formed when larger spheroids are combined together. When the firing pin hits the capsule, the mixture of lead, barium, and antimony in the capsule primer is vaporized due to high temperature and pressure of the explosion, and condenses again on the surface as droplets (12). The homogeneity of compounds in primer droplets is probably caused by the Brownian motion, thermal effects, and general principles of thermodynamics acting on droplet liquids (13). The regular spheres are combined with other spheres to form spheroids. The droplets are again exposed to high temperature and pressure by the explosion of gunpowder, and after leaving the barrel, they form GSR due to rapid cooling. Possible Pb vapor may freeze by coating GSR particles as a shell in proportion to the surface area of GSR. Multi-elemental analysis of chemical content of the resulting GSR can be performed by energy dispersive X-ray spectroscopy (EDS) in a short time with excellent performance (14,15). Figure 2 shows SEM images obtained for ammunition analyzed. To understand the formation mechanism of GSRs, samples almost equal in size in the morphological groups shown in Table 1 were analyzed in the same way. In the formation mechanism of GSRs, the surface morphologies can be divided into three groups. Figure 2 shows (a) irregular spheres, (b) spheres with a bridge formation, and (c) regular spheres. Regular spheres can be formed by splitting off irregular spheres, and irregular spheres can be formed by merging larger spheres or spheroids. Looking at this perspective, these three kinds of particles can be viewed as derivatives of each other. As shown in Fig. 2(c), the elliptic particles can be considered as two spheres connected by a bridge. Therefore, two spheres can be formed when the bridge diminishes (Table 2). Figure 3 shows the EDS spectra for the samples analyzed. EDS is one of the important methods used to determine the elemental and chemical composition (5). Its importance in scientific and technological studies becomes prominent considering its speed and responsiveness, ease of use, and the nondestructive feature of the materials. The characteristic X-rays used in EDS emit when, due to absorption of energy via an inelastic
FIG. 1––2001–2011 firearms calibre distribution examination statistics of TNP, Ankara Regional Criminal Police Laboratory (personal communication).
KARA ET AL.
.
RELATIONSHIP BETWEEN THE MORPHOLOGY AND CHEMICAL COMPOSITION OF GSR
3
TABLE 1––Statistical values for the investigated particles with different morphological property. Number of Particles in the Repeated Search Morphological Property of Particles Spheroid Two spherical with bridge Elliptical Total number of particles
1
2
3
Mean Value X
111 53
140 66
159 77
137 65
57 221
46 252
43 279
49
Standard Deviation
s¼ 30.4 9.1 12
! P ðXX Þ2 1=2 N1
Confidence Range† X ðtr;a sÞ\X\X þ ðtr;a sÞ 6–268 26–104 *–101
*The confidence range for half spherical particles in reality starts at zero value. † where r = 2 a = 0.05 tr,a = 4.303.
FIG. 2––Fading bridge formation with a role of Sb and Pb contamination and GSR particles (a) elliptical particle, (b) two spheres with a bridge, (c) independent spherical particles.
TABLE 2––Intensity of spherical, two spheres with bridge and elliptical particles. Elements, Intensity(c/s) Elliptical Two spherical with bridge Spheroid
Sb
Ba
Pb
C
O
Al
S
Zn
Cu
68.7 57.6
60.4 52.0
0.79 1.42
91.3 72.5
28.7 19.4
2.90 10.2
29.9 45.7
1.95 2.34
3.24 4.42
50.2
48.8
0.98
79.4
30.3
13.2
16.5
1.63
3.15
interaction of some sort, an inner shell electron is ejected from the atom and it is replaced by a higher shell electron. The difference in energies of the two levels is accounted for by the emission of an X-ray equal to that difference. Wavelengths of these radiations of elements are distinctive and different for each element. In other words, these radiations are like a fingerprint of that element. The type of the element (qualitative) is determined by identifying the wavelength of the radiation, and element concentration (quantitative) is determined by measuring the intensity of this radiation precisely. In Fig. 3, the spectra in Fig. 2(a–c) are combined in a single plot for comparison. Particle shapes and dimensions may affect the intensity of X-ray emission. Therefore, particles of similar size and shape were analyzed. As the peak amplitudes created at higher energy values have very small magnitudes, only the peaks up to 10 keV were analyzed.
FIG. 3––EDS spectra of spherical, two spheres with bridge and elliptical particles.
For primer compounds of GSR, the Pb–Ba–Sb particle compositions are considered characteristic of gunshot residues. A small amount of aluminum powder was also identified in ammunition, which was used as fuel (1). In addition, Cu and Zn caused by the coating of the bullet jacket, depending on the type of ammunition, were also identified (16).
4
JOURNAL OF FORENSIC SCIENCES
GSR primer composition strongly affects the structure of the particles (17). As elliptical particles turn into spherical particles, the count values of the elements decrease. Sb mole-fraction and Ba mole-fraction decrease in the structure. The SEM/EDS method has a measurement accuracy of approximately 2%. The decrease in Pb is arguable, as the measured value of intensity (c/s) of Pb is low. Conclusion Characteristic element compositions are important in determining the morphological structures of GSR particles. GSR analysis results show that the basic morphological structure is highly dependent on the chemical composition. The surface morphologies of GSR can be divided into three groups: regular spheres, irregular spheres, and spheres with bridge formation. However, partially broken spheres, hemispheres, or small parts of a sphere were also observed due to explosion. Regular spheres can combine to form spheroids, and irregular spheres can be formed by combination of larger spheroids. Looking from this perspective, these three kinds of particles can be interpreted as derivatives of each other. GSR primer composition (Pb–Ba–Sb) strongly affects the morphological structure of the particles. The particles chosen were analyzed by EDS method to investigate the elemental and chemical composition on morphological structure. It was observed that there is a relationship between morphological structure and concentrations of compounds of the structure. As forms of ammunition have different chemical compounds, shots were fired with the same firearm but different ammunition will lead to different compositions of gunshot residues. Therefore, further studies are needed to investigate the relationship between GSR particles and elemental compositions of cartridge compounds. References 1. Romolo FS, Margot P. Identification of gunshot residue: a critical review. Forensic Sci Int 2001;119:195–211.
2. Zadora G, Brozek-Mucha Z. SEM-EDX – a useful tool for forensic examinations. Mater Chem Phys 2003;81:345–8. 3. Singer RL, Davis D, Houck MM. A survey of gunshot residue analysis methods. J Forensic Sci 1996;41:195–8. 4. Zeichner A, Levin N. More on uniqueness of GSR particles. J Forensic Sci 1997;42:1027–8. 5. Garofano L, Capra M, Ferrari F, Bizzaro GP, DiTullio D, Dell’Olio M, et al. Gunshot residue further studies on particles of environmental and occupation origin. Forensic Sci Int 1999;103:1–21. 6. Zeichner A, Ehrlich S, Shoshani E, Halicz L. Application of lead isotope analysis in shooting incident investigations. Forensic Sci Int 2006;158: 52–64. 7. Rijnders MR, Stamouli A, Bolck A. Comparison of GSR composition occurring at different locations around the firing position. J Forensic Sci 2010;55:616–23. 8. Gialamas DM, Rhodes EF, Sugarman LA. Officers, their weapons and their hands. An empirical study of GSR on the hands of non-shooting police officers. J Forensic Sci 1995;40:1086–9. 9. Mosher PV, McVicar MJ, Randall ED, Sild EH. Gunshot residue-similar particles produced by fireworks. Can Soc Forensic Sci J 1998;43:157–68. 10. Vermeij E, Duvalois W, Webb R, Koeberg M. Morphology and composition of pyrotechnic residues formed at different levels of confinement. J Forensic Sci 2009;186:68–74. 11. Gok O, Simsek G. Explosive materials manufacturing procedures and analysis methods. Ankara, Turkey: MKE Press, 1967. 12. Meng HH, Caddy B. Gunshot residue analysis – a review. J Forensic Sci 1997;42:553–70. 13. Basu S. Formation of gunshot residues. J Forensic Sci 1982;27:72–92. 14. Kosanke KL, Dujay RC, Kosanke B. Characterization of pyrotechnic reaction residue particles by SEM/EDS. J Forensic Sci 2003;48(3):531–7. 15. Izumi N, Yuki O, Qinghui L, Yoshinori N, Keiichi T, Satoshi N. Capability of a TES microcalorimeter SEM-EDS system for forensic analysis of automotive paint and gunshot residue. Surf Interface Anal 2010;42 (5):402–10. 16. Meng HH, Chen YL. Energy dispersive X-ray analysis of bullets commonly encountered in Taiwan. J Forensic Sci 2006;5:21–34. 17. Wrobel HA, Millar JJ, Kijek M. Identification of ammunition from gunshot residues and other cartridge related materials – a preliminary model using.22 caliber rimfire ammunition. J Forensic Sci 1998;43:324–8. Additional information and reprint requests: _ Ilker Kara, M.Sc. Department of Criminal Police Laboratories Turkish National Police 06830, Golbasi, Ankara Turkey E-mail: [email protected]
TECHNICAL NOTE CRIMINALISTICS
Ilker Kara,1,2 Ph.D.; Sefer Bora Lisesivdin,2 Ph.D.; Mehmet Kasap,3 Ph.D.; Elif Er,3 PG.Dip.; and Ugur Uzek,3 B.Sc.
The Relationship Between the Surface Morphology and Chemical Composition of Gunshot Residue Particles
ABSTRACT: In this study, chemical composition and morphology of gunshot residue (GSR) of 9 9 19 mm Parabellum-type MKE (Turkey)-brand ammunition were analyzed by scanning electron microscope and energy dispersive X-ray spectrometer. GSR samples were collected by “swab” technique from the shooter’s right hand immediately after shooting. According to general principles of thermodynamics, it is likely that the structures will have a more regular (homogeneous) spherical form to minimize their surface area due to very high temperatures and pressures that occur during explosion. Studied samples were collected under the same conditions with the same original ammunition, from the same firearm and a single shooter. This is because many other variables may affect size, structure, and composition in addition to the concentrations of elements of the structure. Results indicated that the chemical compositions are effective in the formation of GSR morphological structures. KEYWORDS: forensic science, firearms examination, gunshot residues, primer mixtures, SEM-EDS examination
Gunshot residues are formed as a result of a highly exothermic process in gas, liquid, or solid form when a reaction takes place under high temperature and pressure. The condensed reaction products are accumulated on the shooter’s skin, clothes, or firearm in a partly solidified GSR form. GSR usually has a distinct morphology and composition and consists of burnt and unburnt mostly spheroidal particles of 1.1–50 lm (sometimes larger) in diameter (1). As GSR consists of inorganic substances, it can be analyzed by various methods. Contents of the compounds, quantities, and sizes of a large number of particles can be analyzed visually in a fast and practical manner (manually or automatically), thanks to SEM/EDS (2,3). The elemental content of the particles can be classified by this method (4–8). Experimental studies are intended to identify rare elements, such as lead, barium, and antimony in the primer residues of ammunition (9). It is possible for the reaction products to be more homogeneous (but not necessarily) as pressure, temperature, and vaporization are higher than the surrounding atmosphere during explosion (10). As a result, the structures formed under these conditions tend to be smaller, more spherical, and homogeneous in terms of compound distribution. There is no systematic approach to analyze the relationship between morphological structures, basic components, and amounts of the component in 1
Department of Criminal Police Laboratories, Turkish National Police, 06830 Golbasi, Ankara, Turkey. 2 Department of Physics, Gazi University, 06500 Teknikokullar, Ankara, Turkey. 3 Department of Chemistry, Ankara Criminal Police Laboratory, 06830 Golbasi, Ankara, Turkey. Received 19 Mar. 2014; and in revised form 13 Aug. 2014; accepted 15 Aug. 2014. © 2015 American Academy of Forensic Sciences
these residues formed. If there is a relationship between concentrations and types of the compounds of morphological structures of GSR, then it should be possible to draw conclusions about the formation conditions of GSR. According to general thermodynamic principles, there may be a relationship between components, morphologies, and conditions (i.e., level of confinement) of these residues.
Materials and Methods The subject of the study is the GSR collected by swab technique from the shooter’s hand after firing shots into a water tank. This test was carried out by a single shooter. Three shots were fired with each ammunition type. The samples were collected on aluminum stubs immediately after each shot by a double-sided adhesive tape from the shooter’s right hand. GSR was collected by pressing the stub 100 times to the hand skin including thumb and index finger of the right hand. To prevent any accidental contamination, no other shooter collected samples. For the same reason, the residues were collected from only one person and analyzed with the same strict conditions. This experimental study was carried out at The Directorate Department of the Ankara Criminal Police Laboratory (in Turkish: KPL). All of the tests were carried out in the KPL shooting room. In test shooting, we used a Sarsilmaz brand Mega 2000 Kilinc model semi-automatic 9 mm Parabellum pistol [Machine Chemistry Institute (MKE)] with a 2010 gun cartridge. In the experiment, the barrel of the weapon was cleaned before every shooting. The cleaning process began with mechanical cleaning. Then, the barrel was washed in deionized water in an ultrasonic bath. Lastly, the barrel was dried with dry nitrogen 1
2
JOURNAL OF FORENSIC SCIENCES
gas. This process was performed more than once due to the barrel’s state. The samples were examined with the use of a JEOL/ JSM-6400 scanning electron microscope (SEM), Jeol, Japan. Acceleration voltage was 20 KV, tilt of sample was 0°, and working distance was 39 mm. Images observed were secondary electron images coupled with an INCA energy X-ray spectrometer (Oxford Instruments Ltd., Houston, TX). All analyses were taken from the highest, flattest point on each sample. For the spheres or spheroids, the approximate centers of the structures were chosen. There was a large diversity in the observed particle sizes. However, similarly sized particles were used in the quantitative analyses. As seen from Fig. 1, the 9 9 19 mm Parabellum is the most common handgun caliber among civilians and criminals in Turkey (personal communication). This caliber was selected, and all of the tests in this experimental study were performed with a Parabellum 9 9 19 mm calibre Model 2000 Kilinc Sarsilmazbrand semi-automatic handgun. To provide more reliable results, the test fires were performed using the same brand, in the same year, and with the same ammunition lot (MKEK-2010/3). Using the same brand, year, and ammunition lot reduced the number of variables and prevented the emergence of differences in the primer and gunpowder composition. The common primer composition of a 9 9 19 mm calibre MKEK-brand cartridge was 38% lead styphnate (TNR Pb), 6% tetracene (TRZN), 34% barium nitrate Ba {NO3}, 15% antimony sulfide Sb2S3, 4% pentrite (PETN), and 3% aluminum powder (11). To prevent contamination, the barrel and breech face were cleaned by a three-step cleaning process before every shoot set. The first step of cleaning was mechanical cleaning with a guncleaning brush. A new cleaning brush was used for each shoot set. In the second step, the barrel was washed with deionized water in an ultrasonic bath. In the last step, the barrel was dried with dry nitrogen gas. Results and Discussion Gunshot residues are spherical particles and can be divided into three groups according to their surface structures (Table 1):
regular spheres, spheroids, and irregular spheres. Spheroids are formed by the combination of small spheres with regular surfaces, and irregular spheres are formed when larger spheroids are combined together. When the firing pin hits the capsule, the mixture of lead, barium, and antimony in the capsule primer is vaporized due to high temperature and pressure of the explosion, and condenses again on the surface as droplets (12). The homogeneity of compounds in primer droplets is probably caused by the Brownian motion, thermal effects, and general principles of thermodynamics acting on droplet liquids (13). The regular spheres are combined with other spheres to form spheroids. The droplets are again exposed to high temperature and pressure by the explosion of gunpowder, and after leaving the barrel, they form GSR due to rapid cooling. Possible Pb vapor may freeze by coating GSR particles as a shell in proportion to the surface area of GSR. Multi-elemental analysis of chemical content of the resulting GSR can be performed by energy dispersive X-ray spectroscopy (EDS) in a short time with excellent performance (14,15). Figure 2 shows SEM images obtained for ammunition analyzed. To understand the formation mechanism of GSRs, samples almost equal in size in the morphological groups shown in Table 1 were analyzed in the same way. In the formation mechanism of GSRs, the surface morphologies can be divided into three groups. Figure 2 shows (a) irregular spheres, (b) spheres with a bridge formation, and (c) regular spheres. Regular spheres can be formed by splitting off irregular spheres, and irregular spheres can be formed by merging larger spheres or spheroids. Looking at this perspective, these three kinds of particles can be viewed as derivatives of each other. As shown in Fig. 2(c), the elliptic particles can be considered as two spheres connected by a bridge. Therefore, two spheres can be formed when the bridge diminishes (Table 2). Figure 3 shows the EDS spectra for the samples analyzed. EDS is one of the important methods used to determine the elemental and chemical composition (5). Its importance in scientific and technological studies becomes prominent considering its speed and responsiveness, ease of use, and the nondestructive feature of the materials. The characteristic X-rays used in EDS emit when, due to absorption of energy via an inelastic
FIG. 1––2001–2011 firearms calibre distribution examination statistics of TNP, Ankara Regional Criminal Police Laboratory (personal communication).
KARA ET AL.
.
RELATIONSHIP BETWEEN THE MORPHOLOGY AND CHEMICAL COMPOSITION OF GSR
3
TABLE 1––Statistical values for the investigated particles with different morphological property. Number of Particles in the Repeated Search Morphological Property of Particles Spheroid Two spherical with bridge Elliptical Total number of particles
1
2
3
Mean Value X
111 53
140 66
159 77
137 65
57 221
46 252
43 279
49
Standard Deviation
s¼ 30.4 9.1 12
! P ðXX Þ2 1=2 N1
Confidence Range† X ðtr;a sÞ\X\X þ ðtr;a sÞ 6–268 26–104 *–101
*The confidence range for half spherical particles in reality starts at zero value. † where r = 2 a = 0.05 tr,a = 4.303.
FIG. 2––Fading bridge formation with a role of Sb and Pb contamination and GSR particles (a) elliptical particle, (b) two spheres with a bridge, (c) independent spherical particles.
TABLE 2––Intensity of spherical, two spheres with bridge and elliptical particles. Elements, Intensity(c/s) Elliptical Two spherical with bridge Spheroid
Sb
Ba
Pb
C
O
Al
S
Zn
Cu
68.7 57.6
60.4 52.0
0.79 1.42
91.3 72.5
28.7 19.4
2.90 10.2
29.9 45.7
1.95 2.34
3.24 4.42
50.2
48.8
0.98
79.4
30.3
13.2
16.5
1.63
3.15
interaction of some sort, an inner shell electron is ejected from the atom and it is replaced by a higher shell electron. The difference in energies of the two levels is accounted for by the emission of an X-ray equal to that difference. Wavelengths of these radiations of elements are distinctive and different for each element. In other words, these radiations are like a fingerprint of that element. The type of the element (qualitative) is determined by identifying the wavelength of the radiation, and element concentration (quantitative) is determined by measuring the intensity of this radiation precisely. In Fig. 3, the spectra in Fig. 2(a–c) are combined in a single plot for comparison. Particle shapes and dimensions may affect the intensity of X-ray emission. Therefore, particles of similar size and shape were analyzed. As the peak amplitudes created at higher energy values have very small magnitudes, only the peaks up to 10 keV were analyzed.
FIG. 3––EDS spectra of spherical, two spheres with bridge and elliptical particles.
For primer compounds of GSR, the Pb–Ba–Sb particle compositions are considered characteristic of gunshot residues. A small amount of aluminum powder was also identified in ammunition, which was used as fuel (1). In addition, Cu and Zn caused by the coating of the bullet jacket, depending on the type of ammunition, were also identified (16).
4
JOURNAL OF FORENSIC SCIENCES
GSR primer composition strongly affects the structure of the particles (17). As elliptical particles turn into spherical particles, the count values of the elements decrease. Sb mole-fraction and Ba mole-fraction decrease in the structure. The SEM/EDS method has a measurement accuracy of approximately 2%. The decrease in Pb is arguable, as the measured value of intensity (c/s) of Pb is low. Conclusion Characteristic element compositions are important in determining the morphological structures of GSR particles. GSR analysis results show that the basic morphological structure is highly dependent on the chemical composition. The surface morphologies of GSR can be divided into three groups: regular spheres, irregular spheres, and spheres with bridge formation. However, partially broken spheres, hemispheres, or small parts of a sphere were also observed due to explosion. Regular spheres can combine to form spheroids, and irregular spheres can be formed by combination of larger spheroids. Looking from this perspective, these three kinds of particles can be interpreted as derivatives of each other. GSR primer composition (Pb–Ba–Sb) strongly affects the morphological structure of the particles. The particles chosen were analyzed by EDS method to investigate the elemental and chemical composition on morphological structure. It was observed that there is a relationship between morphological structure and concentrations of compounds of the structure. As forms of ammunition have different chemical compounds, shots were fired with the same firearm but different ammunition will lead to different compositions of gunshot residues. Therefore, further studies are needed to investigate the relationship between GSR particles and elemental compositions of cartridge compounds. References 1. Romolo FS, Margot P. Identification of gunshot residue: a critical review. Forensic Sci Int 2001;119:195–211.
2. Zadora G, Brozek-Mucha Z. SEM-EDX – a useful tool for forensic examinations. Mater Chem Phys 2003;81:345–8. 3. Singer RL, Davis D, Houck MM. A survey of gunshot residue analysis methods. J Forensic Sci 1996;41:195–8. 4. Zeichner A, Levin N. More on uniqueness of GSR particles. J Forensic Sci 1997;42:1027–8. 5. Garofano L, Capra M, Ferrari F, Bizzaro GP, DiTullio D, Dell’Olio M, et al. Gunshot residue further studies on particles of environmental and occupation origin. Forensic Sci Int 1999;103:1–21. 6. Zeichner A, Ehrlich S, Shoshani E, Halicz L. Application of lead isotope analysis in shooting incident investigations. Forensic Sci Int 2006;158: 52–64. 7. Rijnders MR, Stamouli A, Bolck A. Comparison of GSR composition occurring at different locations around the firing position. J Forensic Sci 2010;55:616–23. 8. Gialamas DM, Rhodes EF, Sugarman LA. Officers, their weapons and their hands. An empirical study of GSR on the hands of non-shooting police officers. J Forensic Sci 1995;40:1086–9. 9. Mosher PV, McVicar MJ, Randall ED, Sild EH. Gunshot residue-similar particles produced by fireworks. Can Soc Forensic Sci J 1998;43:157–68. 10. Vermeij E, Duvalois W, Webb R, Koeberg M. Morphology and composition of pyrotechnic residues formed at different levels of confinement. J Forensic Sci 2009;186:68–74. 11. Gok O, Simsek G. Explosive materials manufacturing procedures and analysis methods. Ankara, Turkey: MKE Press, 1967. 12. Meng HH, Caddy B. Gunshot residue analysis – a review. J Forensic Sci 1997;42:553–70. 13. Basu S. Formation of gunshot residues. J Forensic Sci 1982;27:72–92. 14. Kosanke KL, Dujay RC, Kosanke B. Characterization of pyrotechnic reaction residue particles by SEM/EDS. J Forensic Sci 2003;48(3):531–7. 15. Izumi N, Yuki O, Qinghui L, Yoshinori N, Keiichi T, Satoshi N. Capability of a TES microcalorimeter SEM-EDS system for forensic analysis of automotive paint and gunshot residue. Surf Interface Anal 2010;42 (5):402–10. 16. Meng HH, Chen YL. Energy dispersive X-ray analysis of bullets commonly encountered in Taiwan. J Forensic Sci 2006;5:21–34. 17. Wrobel HA, Millar JJ, Kijek M. Identification of ammunition from gunshot residues and other cartridge related materials – a preliminary model using.22 caliber rimfire ammunition. J Forensic Sci 1998;43:324–8. Additional information and reprint requests: _ Ilker Kara, M.Sc. Department of Criminal Police Laboratories Turkish National Police 06830, Golbasi, Ankara Turkey E-mail: [email protected]
