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Portable generator-based XRF instrument for non-destructive analysis at crime scenes
Nuclear Instruments and Methods in Physics Research B 241 (2005) 816–819 www.elsevier.com/locate/nimb
Portable generator-based XRF instrument for non-destructive analysis at crime scenes Jeffrey S. Schweitzer a,*, Jacob I. Trombka b, Samuel Floyd b, Carl Selavka c, Gerald Zeosky d, Norman Gahn e, Timothy McClanahan b, Thomas Burbine b a
e
University of Connecticut, Department of Physics, Unit 3046 Storrs, CT 06269-3046, USA b Goddard Space Flight Center, Code 691, Greenbelt Road, Greenbelt, MD 20771, USA c Massachusetts State Police Crime Laboratory, 59 Horse Pond Road, Sudbury, MA 01776, USA d Forensic Investigation Center, Crime Laboratory Building, 22 State Campus, Albany, NY 12226, USA Assistant District Attorney, Milwaukee County, District AttorneyÕs Office, 821 West State Street, Milwaukee, WI 53233-1427, USA Available online 29 August 2005
Abstract Unattended and remote detection systems find applications in space exploration, telemedicine, teleforensics, homeland security and nuclear non-proliferation programs. The National Institute of Justice (NIJ) and the National Aeronautics and Space AdministrationÕs (NASA) Goddard Space Flight Center (GSFC) have teamed up to explore the use of NASA developed technologies to help criminal justice agencies and professionals investigate crimes. The objective of the program is to produce instruments and communication networks that have application within both NASAÕs space program and NIJ, together with state and local forensic laboratories. A general-purpose X-ray fluorescence system has been built for non-destructive analyses of trace and invisible material at crime scenes. This portable instrument is based on a generator that can operate to 60 kV and a Schottky CdTe detector. The instrument has been shown to be successful for the analysis of gunshot residue and a number of bodily fluids at crime scenes. Ó 2005 Elsevier B.V. All rights reserved. PACS: 82.80.Ej Keywords: Portable XRF instrument; Gunshot residue; Blood; Semen; Schottky CdTe detector; X-ray generator
1. Introduction
*
Corresponding author. Tel.: +1 860 486 6010; fax: +1 860 486 3346. E-mail address: [email protected] (J.S. Schweitzer).
Unattended and remote detection systems find application in such diverse disciplines as space exploration, telemedicine, teleforensics and applications to operations in homeland security and
0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.07.137
J.S. Schweitzer et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 816–819
nuclear non-proliferation programs. With the decrease in funding for research in the various government agencies involved in the development of these technologies, it has become important that dual technology programs be undertaken so that progress can be made in the development of such unattended and remote systems. These developments can then find application in many fields. An example of such a program is the NASA/NIJ program in teleforensics. The National Institute of Justice (NIJ) and the National Aeronautics and Space AdministrationÕs (NASA) Goddard Space Flight Center (GSFC) have teamed up to explore the use of NASA developed technologies to help criminal justice agencies and professionals investigate crimes. The objective of the program is to produce instruments and communication networks that have application within both NASAÕs space program and NIJÕs efforts to enhance crime scene investigations together with state and local forensic laboratories. In order to achieve the volume, weight and power constraints required by both space and terrestrial applications, it was necessary to incorporate solid-state X-ray detectors and a novel X-ray generator into the system designs. Remote sensing at crime scenes is functionally similar to remote sensing of planetary bodies. The X-ray fluorescence system was developed as a general tool for crime scene investigation, including the detection of trace evidence. It has been recognized that reducing the presence of personnel at crime scenes reduces the amount of contamination introduced. It is also recognized that potential evidence not collected at an initial investigation is often lost. To help in the location of possible microscopic or visually invisible evidence, the portable XRF system has been developed. Initial laboratory measurements have demonstrated [1] a number of potentially interesting applications of such a system: the detection of gunshot residue and the discovery of invisible blood and semen. These applications require the detection of X-rays from a wide range of elements, including those with high atomic numbers. Traditional X-ray detectors do not have sufficient efficiency at the higher energies, such as for the K-lines from elements like barium and antimony and the L-lines
817
from lead, all key elements in determining gunshot residue. A solid state Schottky Cadmium Telluride (CT) detector [2] has provided an excellent compromise for sufficiently good energy resolution to detect low energy X-rays with high detection efficiency for determining the higher energy X-ray lines.
2. Instrument description The first system studied under the NASA/NIJ Dual Technology program was a portable X-ray fluorescence (XRF) system. The system consists of a machine X-ray generator, which operates up to 60 kV and a solid state Schottky Cadmium Telluride (CT) detector. The X-ray tube has the source at high voltage and the anode at ground potential. This eliminates the need for high voltage insulation near the detector and sample. The anode material is Mo and a broad X-ray beam is produced that can expose an area of about 1 cm2. The high voltage of 60 kV was selected to provide a high efficiency for exciting K-lines of
Fig. 1. Partially disassembled XRF prototype. The 15 cm ruler is shown for size comparison. The X-ray generator is shown in front of the body for clarity with the beam produced from the anode at the right. The detector is mounted in the upper right of the figure. For measurements of internal samples, the samples are placed inside in the lower right.
818
J.S. Schweitzer et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 816–819 900 Zn
800
Counts
700 600 500 400
Ti
Fe
300 200 100 0 0
5
10
15
20
energy (keV)
Fig. 2. Internal sample measurement position. The SEM stub is centered in the sample position. This block is inserted in the lower right portion of the prototype shown in Fig. 1.
elements of interest. A partially disassembled picture of the prototype is shown is Fig. 1. The sample holding block for internal measurements of samples is shown in Fig. 2. This block is inserted through the lower right of the prototype. An SEM stub is shown mounted in the center position of the sample mounting region. Typical samples are mounted on thin sheets of plastic to reduce the background from coherent scattering. The reduction of coherent scattering in measured spectra is critical for improving the sensitivity to be able to measure microgram quantities of elements of interest. Another key element in the design is the region beneath the sample. This ‘‘beam dump’’ is designed to essentially make it impossible for any X-rays that go through the sample to scatter back into the detector.
3. Forensic materials An example X-ray spectrum obtained with the prototype instrument is shown in Fig. 3, which shows the K-lines from some major components of a red paint chip from a Chevrolet. This is an example of the types of forensic evidence more recently examined. Earlier efforts had focused primarily on gunshot residue, as well as some bodily fluids such as blood and semen [1]. The gunshot residue investigation illustrates the range of effort required to establish measurement standards for
Fig. 3. X-ray spectrum of red paint chip from a Chevrolet taken with the prototype XRF instrument. The most prominent X-ray peaks are labeled.
data collected at crime scenes. A study was made of the literature to identify any possible elemental discrimination that would be possible to identify gunshot residue. The literature data is summarized in Fig. 4. The data suggest that it may be possible to separate shooters from non-shooters by determining the barium and antimony concentrations. The values indicate that a measurement would have to detect on the order of one microgram of these elements to be able to identify gunshot residue. This established the sensitivity criterion for the prototype instrument. However, in addition to providing the sensitivity requirement for the prototype, it was clear that there were not sufficient data to establish the relationship between measured levels of barium and antimony versus positive investigative indications of gunshot residue. Therefore, we, simultaneously with the design of the prototype, undertook a large study [3] of amounts of barium and antimony from gunshot residue for a range of ammunitions and weapons. In parallel, a further study was made [4] of the environmental presence of these elements to ensure that a reliable separation of shooters from non-shooters can be made based on barium and antimony concentrations. The relative constancy of the barium and antimony concentrations, and in particular the antimony to barium relative concentration (see Fig. 4) for a variety of starting primer concentrations, suggests a hightemperature process is responsible for forming the final concentration that is somewhat indepen-
J.S. Schweitzer et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 816–819
819
not be achieved by a single program. An example has been provided of an X-ray fluorescence instrument that has been designed for materials analysis in crime scene investigations and for applications in space science that include: Mars rover instrumentation and the geochemical analysis of planetary bodies.
Acknowledgements The authors are indebted to NASA and NIJ for support of this work.
References
Fig. 4. Literature data on barium and antimony concentration from shooters (triangles) and environmental samples (other symbols).
dent of starting concentrations. Such a process occurs in the formation of solar systems where hightemperature eutectics are formed that are stable at room temperature, but which do not form at room temperature [5]. 4. Conclusions Dual technology programs have allowed the development of scientific instruments that could
[1] J.I. Trombka, J. Schweitzer, C. Selavka, M. Dale, N. Gahn, S. Floyd, J. Marie, M. Hobson, G. Zeosky, K. Martin, T. McClannahan, P. Solomon, E. Gottschang, Space age teleforensics; non-destructive analysis of forensic evidence at crime scenes, Forensic Science International 129 (2002) 1. [2] Y. Eisen, S. Floyd, Schottky, Barrier CdTe(Cl) detectors for planetary missions, Unattended radiation sensor systems for remote applications, in: J.I. Trombka, D.P. Spears, P.H. Solomon (Eds.), AIP Conference Proceedings, Vol. 632, American Institute of Physics, Melville, NY, 2002, p. 142. [3] J. Schweitzer, J. Trombka, S. Floyd, C. Selavka, G. Zeosky, N. Gahn, T. McClanahan, T. Burbine, A portable X-ray fluorescence instrument for forensic investigations. To be presented at the American Association of Forensic Science Meeting, February 2005. [4] A. Harper, J. Schweitzer, J. Trombka, C. Selavka, G. Zeosky, R. Kimble, Survey of trace elemental contributions to the environment: comparison of samples from a diverse group of occupational workers with primer residues from firearms. Presented at the American Association of Forensic Science Meeting, February 2004. [5] F.J.M. Rietmeijer, J.A. Nuth III, A metastable eutectic equilibrium brought down to earth, EOS 81 (2000) 414.
Portable generator-based XRF instrument for non-destructive analysis at crime scenes Jeffrey S. Schweitzer a,*, Jacob I. Trombka b, Samuel Floyd b, Carl Selavka c, Gerald Zeosky d, Norman Gahn e, Timothy McClanahan b, Thomas Burbine b a
e
University of Connecticut, Department of Physics, Unit 3046 Storrs, CT 06269-3046, USA b Goddard Space Flight Center, Code 691, Greenbelt Road, Greenbelt, MD 20771, USA c Massachusetts State Police Crime Laboratory, 59 Horse Pond Road, Sudbury, MA 01776, USA d Forensic Investigation Center, Crime Laboratory Building, 22 State Campus, Albany, NY 12226, USA Assistant District Attorney, Milwaukee County, District AttorneyÕs Office, 821 West State Street, Milwaukee, WI 53233-1427, USA Available online 29 August 2005
Abstract Unattended and remote detection systems find applications in space exploration, telemedicine, teleforensics, homeland security and nuclear non-proliferation programs. The National Institute of Justice (NIJ) and the National Aeronautics and Space AdministrationÕs (NASA) Goddard Space Flight Center (GSFC) have teamed up to explore the use of NASA developed technologies to help criminal justice agencies and professionals investigate crimes. The objective of the program is to produce instruments and communication networks that have application within both NASAÕs space program and NIJ, together with state and local forensic laboratories. A general-purpose X-ray fluorescence system has been built for non-destructive analyses of trace and invisible material at crime scenes. This portable instrument is based on a generator that can operate to 60 kV and a Schottky CdTe detector. The instrument has been shown to be successful for the analysis of gunshot residue and a number of bodily fluids at crime scenes. Ó 2005 Elsevier B.V. All rights reserved. PACS: 82.80.Ej Keywords: Portable XRF instrument; Gunshot residue; Blood; Semen; Schottky CdTe detector; X-ray generator
1. Introduction
*
Corresponding author. Tel.: +1 860 486 6010; fax: +1 860 486 3346. E-mail address: [email protected] (J.S. Schweitzer).
Unattended and remote detection systems find application in such diverse disciplines as space exploration, telemedicine, teleforensics and applications to operations in homeland security and
0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.07.137
J.S. Schweitzer et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 816–819
nuclear non-proliferation programs. With the decrease in funding for research in the various government agencies involved in the development of these technologies, it has become important that dual technology programs be undertaken so that progress can be made in the development of such unattended and remote systems. These developments can then find application in many fields. An example of such a program is the NASA/NIJ program in teleforensics. The National Institute of Justice (NIJ) and the National Aeronautics and Space AdministrationÕs (NASA) Goddard Space Flight Center (GSFC) have teamed up to explore the use of NASA developed technologies to help criminal justice agencies and professionals investigate crimes. The objective of the program is to produce instruments and communication networks that have application within both NASAÕs space program and NIJÕs efforts to enhance crime scene investigations together with state and local forensic laboratories. In order to achieve the volume, weight and power constraints required by both space and terrestrial applications, it was necessary to incorporate solid-state X-ray detectors and a novel X-ray generator into the system designs. Remote sensing at crime scenes is functionally similar to remote sensing of planetary bodies. The X-ray fluorescence system was developed as a general tool for crime scene investigation, including the detection of trace evidence. It has been recognized that reducing the presence of personnel at crime scenes reduces the amount of contamination introduced. It is also recognized that potential evidence not collected at an initial investigation is often lost. To help in the location of possible microscopic or visually invisible evidence, the portable XRF system has been developed. Initial laboratory measurements have demonstrated [1] a number of potentially interesting applications of such a system: the detection of gunshot residue and the discovery of invisible blood and semen. These applications require the detection of X-rays from a wide range of elements, including those with high atomic numbers. Traditional X-ray detectors do not have sufficient efficiency at the higher energies, such as for the K-lines from elements like barium and antimony and the L-lines
817
from lead, all key elements in determining gunshot residue. A solid state Schottky Cadmium Telluride (CT) detector [2] has provided an excellent compromise for sufficiently good energy resolution to detect low energy X-rays with high detection efficiency for determining the higher energy X-ray lines.
2. Instrument description The first system studied under the NASA/NIJ Dual Technology program was a portable X-ray fluorescence (XRF) system. The system consists of a machine X-ray generator, which operates up to 60 kV and a solid state Schottky Cadmium Telluride (CT) detector. The X-ray tube has the source at high voltage and the anode at ground potential. This eliminates the need for high voltage insulation near the detector and sample. The anode material is Mo and a broad X-ray beam is produced that can expose an area of about 1 cm2. The high voltage of 60 kV was selected to provide a high efficiency for exciting K-lines of
Fig. 1. Partially disassembled XRF prototype. The 15 cm ruler is shown for size comparison. The X-ray generator is shown in front of the body for clarity with the beam produced from the anode at the right. The detector is mounted in the upper right of the figure. For measurements of internal samples, the samples are placed inside in the lower right.
818
J.S. Schweitzer et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 816–819 900 Zn
800
Counts
700 600 500 400
Ti
Fe
300 200 100 0 0
5
10
15
20
energy (keV)
Fig. 2. Internal sample measurement position. The SEM stub is centered in the sample position. This block is inserted in the lower right portion of the prototype shown in Fig. 1.
elements of interest. A partially disassembled picture of the prototype is shown is Fig. 1. The sample holding block for internal measurements of samples is shown in Fig. 2. This block is inserted through the lower right of the prototype. An SEM stub is shown mounted in the center position of the sample mounting region. Typical samples are mounted on thin sheets of plastic to reduce the background from coherent scattering. The reduction of coherent scattering in measured spectra is critical for improving the sensitivity to be able to measure microgram quantities of elements of interest. Another key element in the design is the region beneath the sample. This ‘‘beam dump’’ is designed to essentially make it impossible for any X-rays that go through the sample to scatter back into the detector.
3. Forensic materials An example X-ray spectrum obtained with the prototype instrument is shown in Fig. 3, which shows the K-lines from some major components of a red paint chip from a Chevrolet. This is an example of the types of forensic evidence more recently examined. Earlier efforts had focused primarily on gunshot residue, as well as some bodily fluids such as blood and semen [1]. The gunshot residue investigation illustrates the range of effort required to establish measurement standards for
Fig. 3. X-ray spectrum of red paint chip from a Chevrolet taken with the prototype XRF instrument. The most prominent X-ray peaks are labeled.
data collected at crime scenes. A study was made of the literature to identify any possible elemental discrimination that would be possible to identify gunshot residue. The literature data is summarized in Fig. 4. The data suggest that it may be possible to separate shooters from non-shooters by determining the barium and antimony concentrations. The values indicate that a measurement would have to detect on the order of one microgram of these elements to be able to identify gunshot residue. This established the sensitivity criterion for the prototype instrument. However, in addition to providing the sensitivity requirement for the prototype, it was clear that there were not sufficient data to establish the relationship between measured levels of barium and antimony versus positive investigative indications of gunshot residue. Therefore, we, simultaneously with the design of the prototype, undertook a large study [3] of amounts of barium and antimony from gunshot residue for a range of ammunitions and weapons. In parallel, a further study was made [4] of the environmental presence of these elements to ensure that a reliable separation of shooters from non-shooters can be made based on barium and antimony concentrations. The relative constancy of the barium and antimony concentrations, and in particular the antimony to barium relative concentration (see Fig. 4) for a variety of starting primer concentrations, suggests a hightemperature process is responsible for forming the final concentration that is somewhat indepen-
J.S. Schweitzer et al. / Nucl. Instr. and Meth. in Phys. Res. B 241 (2005) 816–819
819
not be achieved by a single program. An example has been provided of an X-ray fluorescence instrument that has been designed for materials analysis in crime scene investigations and for applications in space science that include: Mars rover instrumentation and the geochemical analysis of planetary bodies.
Acknowledgements The authors are indebted to NASA and NIJ for support of this work.
References
Fig. 4. Literature data on barium and antimony concentration from shooters (triangles) and environmental samples (other symbols).
dent of starting concentrations. Such a process occurs in the formation of solar systems where hightemperature eutectics are formed that are stable at room temperature, but which do not form at room temperature [5]. 4. Conclusions Dual technology programs have allowed the development of scientific instruments that could
[1] J.I. Trombka, J. Schweitzer, C. Selavka, M. Dale, N. Gahn, S. Floyd, J. Marie, M. Hobson, G. Zeosky, K. Martin, T. McClannahan, P. Solomon, E. Gottschang, Space age teleforensics; non-destructive analysis of forensic evidence at crime scenes, Forensic Science International 129 (2002) 1. [2] Y. Eisen, S. Floyd, Schottky, Barrier CdTe(Cl) detectors for planetary missions, Unattended radiation sensor systems for remote applications, in: J.I. Trombka, D.P. Spears, P.H. Solomon (Eds.), AIP Conference Proceedings, Vol. 632, American Institute of Physics, Melville, NY, 2002, p. 142. [3] J. Schweitzer, J. Trombka, S. Floyd, C. Selavka, G. Zeosky, N. Gahn, T. McClanahan, T. Burbine, A portable X-ray fluorescence instrument for forensic investigations. To be presented at the American Association of Forensic Science Meeting, February 2005. [4] A. Harper, J. Schweitzer, J. Trombka, C. Selavka, G. Zeosky, R. Kimble, Survey of trace elemental contributions to the environment: comparison of samples from a diverse group of occupational workers with primer residues from firearms. Presented at the American Association of Forensic Science Meeting, February 2004. [5] F.J.M. Rietmeijer, J.A. Nuth III, A metastable eutectic equilibrium brought down to earth, EOS 81 (2000) 414.