AIRPORT PASSENGER
SCREENING USING
BACKSCATTER
X-RAY MACHINES
Compliance with Standards
Committee on Airport Passenger Screening: Backscatter X-Ray Machines
National Materials and Manufacturing Board
Division on Engineering and Physical Sciences
and
Nuclear and Radiation Studies Board
Division on Earth and Life Sciences
THE NATIONAL ACADEMIES PRESS
Washington, DC
www.nap.edu
THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001
This study was supported by Contract/Grant No. HSHQDC-11-D-00009 between the National Academy of Sciences and the Department of Homeland Security. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.
International Standard Book Number-13: 978-0-309-37133-9
International Standard Book Number-10: 0-309-37133-3
DOI: 10.17226/21710
Cover Image: A common scene at a fictional airport employing passenger screening using a backscatter X-ray machine. Artist: Erik Svedberg. Image created by ray tracing, where computational rays of light backscatter, reflect, or are transmitted throughout the geometry of the scene to paint the full picture.
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Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2015. Airport Passenger Screening Using Backscatter X-Ray Machines: Compliance with Standards. Washington, DC: The National Academies Press.
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COMMITTEE ON AIRPORT PASSENGER SCREENING: BACKSCATTER X-RAY MACHINES
HARRY E. MARTZ, JR., Lawrence Livermore National Laboratory, Chair
BARBARA J. McNEIL, Harvard Medical School, Vice Chair
SALLY A. AMUNDSON, Columbia University Medical Center
DAVID E. ASPNES, North Carolina State University
ARNOLD BARNETT, Massachusetts Institute of Technology
THOMAS B. BORAK, Colorado State University
LESLIE A. BRABY, Texas A&M University, College Station
MATS P.E. HEIMDAHL, University of Minnesota, Minneapolis
SANDRA L. HYLAND, Consultant, Falls Church, Virginia
SHELDON H. JACOBSON, University of Illinois, Urbana-Champaign
JAY S. LOEFFLER, Massachusetts General Hospital
C. KUMAR N. PATEL, Pranalytica, Inc.
MAURO SARDELA, University of Illinois, Urbana-Champaign
ZHI-MIN YUAN, Harvard School of Public Health
Staff
JAMES LANCASTER, Acting Director, National Materials and Manufacturing Board
ERIK B. SVEDBERG, Senior Program Officer, Study Director
OURANIA KOSTI, Senior Program Officer
HYEKYUNG (CLARISSE) KIM, Christine Mirzayan Science and Technology Policy Graduate Fellow
HEATHER LOZOWSKI, Financial Associate
NEERAJ P. GORKHALY, Research Associate
JOSEPH PALMER, Senior Project Assistant
NATIONAL MATERIALS AND MANUFACTURING BOARD
ROBERT E. SCHAFRIK, GE Aircraft Engines (retired), Chair
MICHAEL BASKES, Mississippi State University
JIM C.I. CHANG, North Carolina State University
JENNIE HWANG, H-Technologies Group
SANDRA L. HYLAND, Consultant, Falls Church, Virginia
SUNDARESAN JAYARAMAN, Georgia Institute of Technology
ROBERT H. LATIFF, R. Latiff Associates
MICHAEL F. MCGRATH, McGrath Analytics LLC
CELIA MERZBACHER, Semiconductor Research Corporation
EDWARD MORRIS, National Center for Defense Manufacturing
VINCENT J. RUSSO, Aerospace Technologies Associates, LLC
GREG TASSEY, University of Washington
HAYDN G. WADLEY, University of Virginia
BEN WANG, Georgia Institute of Technology
Staff
JAMES LANCASTER, Acting Director
ERIK B. SVEDBERG, Senior Program Officer
HEATHER LOZOWSKI, Financial Associate
NEERAJ P. GORKHALY, Research Associate
JOSEPH PALMER, Senior Project Assistant
NUCLEAR AND RADIATION STUDIES BOARD
ROBERT C. DYNES, University of California, San Diego, Chair
BARBARA J. McNEIL, Harvard Medical School, Vice Chair
JOHN S. APPLEGATE, Indiana University School of Law
DAVID J. BRENNER, Columbia University
MARGARET S.Y. CHU, M.S. Chu & Associates, LLC
MICHAEL L. CORRADINI, University of Wisconsin, Madison
TISSA H. ILLANGASEKARE, Colorado School of Mines
CAROL M. JANTZEN, Savannah River National Laboratory
ANNIE B. KERSTING, Lawrence Livermore National Laboratory
MARTHA S. LINET, National Institutes of Health
FRED A. METTLER, JR., New Mexico VA Health Care System
NANCY JO NICHOLAS, Los Alamos National Laboratory
LAWRENCE T. PAPAY,1 PQR, LLC
DANIEL O. STRAM, University of Southern California, Los Angeles
RICHARD J. VETTER, Mayo Clinic (retired)
SERGEY V. YUDINTSEV, Russian Academy of Sciences
Staff
KEVIN D. CROWLEY, Director
JENNIFER HEIMBERG, Senior Program Officer
OURANIA KOSTI, Senior Program Officer
TONI GREENLEAF, Administrative and Financial Associate
LAURA D. LLANOS, Administrative and Financial Associate
DARLENE GROS, Senior Program Assistant
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1 Deceased on July 28, 2014.
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Preface
The Department of Homeland Security (DHS) requested that the National Research Council (NRC) provide an independent study of the radiation exposures resulting from X-ray backscatter advanced imaging technology (AIT) systems used in screening travelers in U.S. airports. According to the Transportation Security Administration (TSA), a component of DHS responsible for the security of the transportation systems in the United States, AIT systems provide enhanced security benefits by detecting both metallic and non-metallic threat items, including weapons, explosives, and other concealed objects on passengers, some of which would not be detected by walk-through metal detectors.1 X-ray backscatter AITs were deployed in U.S airports in 2008 and subsequently removed from all airports by June 2013 due to privacy concerns. This removal was an effect of Congress stipulating in the FAA Modernization and Reform Act of 20122 that all TSA body scanners should have automatic target recognition, thus eliminating the need for a screener to view the image of the person being scanned, something manufacturers
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1 General Accountability Office, Transportation Security Administration: Progress and Challenges Faced in Strengthening Three Key Security Programs, Statement of Stephen M. Lord, Director, Homeland Security and Justice Issues, Testimony Before the Committee on Oversight and Government Reform and Committee on Transportation and Infrastructure, U.S. House of Representatives, GAO-12-541T, March 26, 2012, http://oversight.house.gov/wp-content/uploads/2012/03/3-26-12-Joint-TI-Lord-Testimony.pdf.
2 U.S. House of Representatives, FAA Modernization and Reform Act of 2012 Conference Report to Accompany H.R. 658, 11th Congress, Report 112-381, February 1, 2012, http://www.gpo.gov/fdsys/pkg/CRPT-112hrpt381/pdf/CRPT-112hrpt381.pdf.
failed to implement. TSA is looking to deploy a second-generation X-ray backscatter AIT equipped with privacy software to eliminate production of an image of the person being screened.
This study aims to address concerns about exposure to radiation from X-ray backscatter AITs raised by Congress, individuals within the scientific community, and others. It was carried out by a committee of experts appointed by the NRC. The Committee on Airport Passenger Screening: Backscatter X-Ray Machines consisted of 14 members with expertise that spans the disciplines relevant to the study task: radiation physics and dosimetry, radiation biology, diagnostic and therapeutic radiology, materials science, systems and electrical engineering, manufacturing testing and evaluation, aviation safety, software safety, and statistics.
Three factors made the committee’s task challenging:
- There were no X-ray backscatter AIT systems deployed in U.S. airports at the time the committee started and completed its examination. In fact, the committee did not have access to any machines until about 8 months after it was convened, and after that it had limited access to the AITs and limited time to complete its work.
- The X-ray backscatter AIT systems available to the committee for examination were located in facilities belonging to government agencies and either under preliminary testing or used as a reference. Therefore, no destructive testing could be done; the committee was thus unable to perform a complete examination of the systems’ safety interlocks, which prevent overexposures of the people being screened. Such an examination would have potentially involved damaging the machines while they were in operation to document whether the machines safely terminated operations in response to the destructive testing.
- Much of the information related to the design and operation of the AITs is excluded from public domain for reasons of national security or because of its proprietary and confidential nature.
Despite the above-mentioned factors, the committee was able to complete its radiation dose study of two X-ray backscatter AIT systems representing past and possibly future screening of travelers in U.S. airports. The committee hopes that its findings and recommendations will be useful to the general public and TSA, the sponsor, and others in evaluating the radiation exposure of any future X-ray backscatter AIT and examining the adequacy of the system design, including safety interlocks to avoid overexposures.
In closing, we thank the committee members for their exceptional efforts in carrying out this investigation and preparing this report. We and the committee
also thank the NRC staff for facilitating this study. Senior program officers Erik Svedberg and Ourania Kosti organized the committee meetings and the committee’s work and assisted the committee with report writing and review. Program assistant Joe Palmer and research associate Neeraj Gorkhaly managed the logistics of the meetings and all the daily tasks.
The committee also thanks those who were guest speakers at its meetings and who added to the committee members’ understanding of X-ray backscatter and the issues surrounding it:
Domenic Bianchini, Transportation Security Administration,
Wesley E. Bolch, University of Florida,
John Boone, University of California, Davis Medical Center,
Richard Burdette, Transportation Security Administration,
Frank Cartwright, Transportation Security Administration,
Jack Glover, National Institute of Standards and Technology,
David E. Hintenlang, University of Florida,
Larry T. Hudson, National Institute of Standards and Technology,
Daniel Kassiday, Food and Drug Administration,
Ronnie Minniti, National Institute of Standards and Technology,
Jill M. Segraves, Transportation Security Administration, and
Steve Smith, Tech84.
We also wish to thank Wesley E. Bolch, Shannon E. O’Reilly, Matthew R. Maynard, and Elliott J. Stepusin of the computation team and David E. Hintenlang and Sadije Redzovic of the physical dosimetry team in the Department of Biomedical Engineering at the University of Florida, Gainesville.
Harry Martz, Chair, and Barbara McNeil, Vice Chair
Committee on Airport Passenger Screening:
Backscatter X-Ray Machines
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Acknowledgment of Reviewers
This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:
William Brinkman, Princeton University,
John Boone, University of California, Davis,
Carl Crawford, Csuptwo, LLC,
Ward Plummer, Louisiana State University,
David Schauer, International Commission on Radiation Units and Measurements,
Steven Simon, National Institutes of Health, and
Richard Toohey, M.H. Chew & Associates.
Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the views presented in the report, nor did they see the final draft of the report before its release. The review of this report was overseen by Etta D. Pisano, Medical University of South Carolina,
and Robert A. Frosch, Harvard University, who were responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this summary rests entirely with the committee and the institution.
Contents
Advanced Imaging Technology in U.S. Airports
Safety Concerns Related to X-Ray Backscatter AIT
Strategy to Address the Study Charge
Information Gathering and Challenges
2 RADIATION PHYSICS RELEVANT TO ADVANCED IMAGING TECHNOLOGY
The Physics of X-Ray Absorption
Beam Attenuation and Deposited Energy
4 DOSIMETRY FOR X-RAY BACKSCATTER ADVANCED IMAGING TECHNOLOGY
Relationship Between Kerma and Absorbed Dose
5 RADIATION PROTECTION STANDARDS
Radiation Health Effects and Risks at Low Doses
System Design, Interlocks, and Operating Procedures
Indicators and Safety Interlocks
6 REVIEW OF X-RAY BACKSCATTER ADVANCED IMAGING TECHNOLOGY STUDIES
Comparing Radiation Measurements
Summary of Measurements from Reviewed Studies
Summary of the Interlock Topic from Reviewed Studies
Other Studies and Considerations
The Dose from Compton Backscatter Screening
Letter to the Presidential Science and Technology Advisor
Estimation of Organ and Effective Dose Due to Compton Backscatter Security Scans
Security Analysis of a Full-Body Scanner
Findings and Recommendations on Exposure and Dose
Depth Dose Distribution Measurements
Dose Outside Inspection Area Potentially Affecting Bystanders
Determination of the Kerma per Screening Outside the Inspection Area
AS&E SmartCheck System Measurement Results and System Design
Percent Depth Dose Measurements
Committee Review of the AS&E SmartCheck System Design
The Rapiscan Secure 1000 System Measurement Results and System Design
Committee Review of the Rapiscan Secure 1000 System Design
Summary of Key Findings for Both Measured Systems
B Glossary, Acronyms, and Abbreviations
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