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Passenger screening at commercial airports in the United States has gone through significant changes since the events of September 11, 2001. In response to increased concern over terrorist attacks on aircrafts, the Transportation Security Administration (TSA) has deployed security systems of advanced imaging technology (AIT) to screen passengers at airports. To date (December 2014), TSA has deployed AITs in U.S. airports of two different technologies that use different types of radiation to detect threats: millimeter wave and X-ray backscatter AIT systems. 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. 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 in order to alleviate these concerns.

This report reviews previous studies as well as current processes used by the Department of Homeland Security and equipment manufacturers to estimate radiation exposures resulting from backscatter X-ray advanced imaging technology system use in screening air travelers. Airport Passenger Screening Using Backscatter X-Ray Machines examines whether exposures comply with applicable health and safety standards for public and occupational exposures to ionizing radiation and whether system design, operating procedures, and maintenance procedures are appropriate to prevent over exposures of travelers and operators to ionizing radiation. 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.

Product Details

ISBN-13: 9780309371339
Publisher: National Academies Press
Publication date: 01/10/2016
Pages: 202
Product dimensions: 6.90(w) x 9.90(h) x 0.60(d)

Table of Contents

Summary 1

1 Introduction 9

Advanced Imaging Technology in U.S. Airports 9

Safety Concerns Related to X-Ray Backscatter AIT 16

The Study Request 21

Strategy to Address the Study Charge 22

Information Gathering and Challenges 25

Report Organization 25

2 Radiation Physics Relevant to Advanced Imaging Technology 27

The Physics of X-Ray Absorption 27

Beam Attenuation and Deposited Energy 30

3 X-Ray Backscatter Advanced Imaging Technology 33

Rapiscan Secure 1000 34

AS&E SmartCheck 37

Tek84 Ait84 38

4 Dosimetry for X-Ray Backscatter Advanced Imaging Technology 40

X-Ray Spectra 41

Kerma 41

Absorbed Dose 43

Effective Dose 43

Reference Effective Dose 46

Relationship Between Kerma and Absorbed Dose 46

5 Radiation Protection Standards 48

Dose 48

Radiation Health Effects and Risks at Low Doses 51

System Design, Interlocks, and Operating Procedures 52

Indicators and Safety Interlocks 52

Operational Procedures 54

6 Review of X-Ray Backscatter Advanced Imaging Technology Studies 56

Comparing Radiation Measurements 57

The JHU/APL Report 60

The NIST Report 63

The AAPM Report 66

The USAPHC Report 69

The FDA Report 71

Summary of Measurements from Reviewed Studies 73

Summary of the Interlock Topic from Reviewed Studies 74

Other Studies and Considerations 75

The Dose from Compton Backscatter Screening 75

Letter to the Presidential Science and Technology Advisor 78

Estimation of Organ and Effective Dose Due to Compton Backscatter Security Scans 81

Security Analysis of a Full-Body Scanner 81

Findings and Recommendations on Exposure and Dose 82

Individual Being Screened 82

Kerma Measurements 83

Half-Value Layer Measurements 83

Depth Dose Distribution Measurements 83

Dose Outside Inspection Area Potentially Affecting Bystanders 84

7 Measurements, Dose Calculations, and System Design For X-Ray Backscatter Advanced Imaging Technology Systems 86

Measurement Procedures 87

Measuring Half-Value Layer 87

Measuring Percent Depth Dose 90

Measuring Air Kerma 92

Determination of the Kerma per Screening Outside the Inspection Area 93

AS&E SmartCheck System Measurement Results and System Design 95

Half-Value Layer Results 95

Percent Depth Dose Measurements 96

Air Kerma Results 100

Committee Review of the AS&E SmartCheck System Design 103

The Rapiscan Secure 1000 System Measurement Results and System Design 103

Half-Value Layer Results 105

Percent Depth Dose Results 107

Air Kerma Results 113

Committee Review of the Rapiscan Secure 1000 System Design 114

Summary of Key Findings for Both Measured Systems 122

Dose Computations 123

Objectives 123

Introduction 123

X-Ray Source Term 126

Summary 148

Results 149

Findings and Recommendations 151

Measurements 151

System Design 151

Dose Computations 152


A Statement of Task 157

B Glossary, Acronyms, and Abbreviations 158

C Organ Absorbed Doses 163

D Summary of Statistics from Previous Studies 170

E Biographies of Committee Members and Contractors 176

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