Position Paper on X-ray Diffraction for Aviation Security

In Brief

X-ray diffraction (XRD) provides a ‘fingerprint’ of materials based on their atomic structure – information that is fundamentally orthogonal to, and therefore complementary to, the density-based features of existing CT and transmission X-ray systems.

Incorporating XRD into aviation security screening workflows offers the prospect of dramatically reducing false alarm rates, enabling definitive automated identification of explosive threats and narcotics that current technology cannot reliably distinguish from benign items, and supporting the next generation of self-service and automated screening architectures in hold-baggage and checkpoint scenarios. Regulators, agencies, and industry partners are urged to prioritize investment in XRD qualification, certification, and operational deployment – and to incorporate XRD into the technology roadmaps that will define the future of security screening.

The Screening Challenge

Today’s aviation security and customs screening infrastructure relies heavily on X-ray transmission and computed tomography (CT) systems to detect explosive devices, weapons, and contraband within baggage and cargo. These systems have driven decades of improvement in imaging capability, along with some commensurate improvements in screening capability. However, CT faces a fundamental limitation: the features it provides – primarily bulk density (CT number) and effective atomic number (Zeff) – are insufficient to uniquely identify many materials of interest. Many benign items and many threat materials occupy overlapping ranges of density and Z^eff, making definitive discrimination based on transmission or CT data alone challenging, prone to false alarms, and imposes a significant operational burden. At aviation security checkpoints, alarmed bags are diverted to secondary inspection involving manual searches, explosive trace detection (ETD) swabs, bottle liquid scanners (BLSs), or physical disassembly of electronic devices. In checked baggage environments, unresolved CT al arms require manual bag opening. These procedures create bottlenecks, consume screener resources, frustrate travelers, and in many cases still fail to achieve a definitive threat identification.

X-Ray Diffraction Screening: A New Dimension of Material Specificity

X-ray diffraction (XRD) has been the gold standard for material structure analysis across chemistry, materials science, and pharmaceuticals for more than a century¹. Unlike transmission X-ray, which measures the attenuation of X-rays through bulk material, XRD measures the scattering of X-rays from the atomic lattice of a substance – producing a unique, characteristic diffraction pattern, or ‘fingerprint’, that encodes the material’s atomic structure. Critically, XRD signatures are orthogonal to density and Zeff: two materials with identical densities can have entirely distinct XRD fingerprints. This orthogonality makes XRD ideally suited to complement CT systems, providing an independent dimension of material information that resolves ambiguities that transmission imaging alone cannot. XRD system maturity and performance in explosives detection have been proven over decades in airport operation².

Table 1: XDR value proposition for complementing transmission & CT imaging

Recommendations

Regulators, agencies, and industry stakeholders should consider the following actions to realize the full potential of X-ray diffraction for Aviation Security screening:

1. Incorporate into formal technology roadmaps.

   Aviation security and customs screening technology roadmaps including TSA’s Capabilities and Requirements Analysis and ECAC’s technology pipeline – should explicitly recognize XRD as a priority technology category and establish clear qualification and certification pathways for operational deployment.

2. Invest in operational data collection programs.

   Funding stream-of-commerce data collection at aviation screening sites is essential to characterize XRD performance in real-world environments and build the evidence base required for procurement decisions.

3. Avoid diluting detection standards.

   Standards must be technology agnostic and avoid being reduced to meet existing technology capability, specifically where combinations of technology will meet the full requirements. This ensures alternative technologies, such as XRD, can find space and opportunity within aviation security, promoting innovation and enhancing capability.

4. Develop open standards for multimodal screening integration.

   Open standards for XRD data formats, interfaces, and performance evaluation methodologies should be developed in collaboration with industry, enabling vendor-agnostic integration of XRD into existing CT and transmission screening infrastructure and preventing proprietary lock-in.

 

References

¹ https://pubs.acs.org/doi/10.1021/ed500343x

² https://doi.org/10.1016/j.apradiso.2008.08.006