Airport Passenger Screening Using Backscatter X-Ray Machines Compliance with Standards (2015) / Chapter Skim
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According to TSA, AIT systems provide enhanced security benefits by detecting both metallic and nonmetallic threat items, including weapons, explosives, and other concealed objects on passengers that would not be detected by walk-through metal detectors. To date (December 2014)
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AIT system design, operating procedures, and maintenance procedures are appropriate to prevent over exposures of travelers and operators to radiation. The complete statement of task for the NRC Committee on Airport Passenger Screening: Backscatter X-Ray Machines is shown in Appendix A
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tasked with making dosimetry and beam characteristics measurements for both the Rapiscan Secure 1000 and AS&E SmartCheck AITs. A second NRC-contracted team performed detailed computations to screened passengers using Monte Carlo methods with a suite of digitized human phantoms (see Chapter 7)
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Additional technical details to support these key findings and recommendations are presented in Chapters 6 and 7 of the report. KEY FINDINGS AND RECOMMENDATIONS Dose Reported in Previous Investigations Individual Being Screened Key Finding: Previous radiation dose studies employed different methodolo gies and instrumentation to estimate the dose delivered by Rapiscan Secure 1000 X-ray backscatter AITs.
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Based on these improvements in approach, the committee has the following key finding: Key Finding: For either the Rapiscan Secure 1000 or the AS&E SmartCheck systems, as determined by the committee for adults and children, • The effective doses are about the same as those calculated following the simplified formula for the reference effective dose identified by the ANSI/ HPS N43.17-2009 standard; • The effective doses are lower than those in previous reports using plane parallel X-ray beams with stylized geometrical (low-fidelity) human phantoms; and • Sensitivity analysis showed that under a range of different conditions, including passenger position in the AIT system and increases in the energy (i.e., by increasing the tube high voltage)
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In general, the committee found the following: Key Finding: Under routine operations, the computed effective doses using computational X-ray sources and scanning geometries, coupled with the digi tized hybrid phantoms, are similar to the ANSI reference effective dose and an order of magnitude below the limit of 250 nSv/screen, as set forth in the applicable ANSI/HPS N43.17-2009 standard. Key Finding: The agreement between the estimated dose results from the NRC subcontractor and the results from earlier studies confirms that the reference effective dose calculations performed in the previous studies were adequate to establish compliance with effective dose limits recommended in the ANSI/ HPS N43.17-2009 standard.
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With the above limitations noted, having evaluated as many aspects of the AIT systems' safety interlocks as possible, both mechanical and electrical, and combining that knowledge with the measurements and computations performed, the committee can make the following statements: Key Finding: It appears that the X-ray backscatter AIT systems adhere to the recommended safety mechanisms described in the ANSI/HPS N43.17-2009 standard. Key Finding: Acceptance tests and periodic inspection tests guided by the safety inspection forms previously used during deployment are sufficient to meet the indicators, controls, and safety interlocks requirements of the ANSI/ HPS N43.17-2009 standard.
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Key Recommendation: Future X-ray AITs should have some independent mechanism to ensure that the AIT does not screen any person for longer than the time needed to acquire the appropriate image while keeping radiation exposure compliant with the safety principle of as low as (is) reasonably achievable.
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