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The development of a backscatter X-ray system for cargo & vehicle screening

7 March 2012

Nick Calvert

This research is funded by RAPISCAN SYSTEMS. The inspection of cargo and vehicles at transit points has become almost universally mandatory; and our security often depends on individual operators accurately analysing thousands of images from screening devices. Non-invasive inspection is typically achieved using transmission and/or backscatter based X-ray imaging systems. Backscatter based systems typically utilise a constant potential X-ray source and a rotating collimator to form a flying spot which passes over the surface of the object under inspection. Some of the X-rays that backscatter away from the surface can be captured by a detector located at some distance from the surface of the object. Using trigonometry, it is possible to form a 2D-image of the object as it passes past the source.

The intensity of the backscattered signal is inversely proportional to the fourth power of the distance from the source to the object. For objects with curved sides, this dependence leads to distortion in the image displayed to the operator.  In an effort to overcome these distortions, this project aims to develop a backscatter X-ray screening system for Cargo & Vehicle screening that uses the finite velocity of the X-ray signal to gain knowledge of the surface profile of the object under inspection.

The project proposes using a pulsed X-ray source with a rotating collimator and detecting the backscattered X-rays as before. As well as detecting the backscattered signal, the detectors are now sampled at various time intervals to get an estimate of the distance between the source and the object under inspection. This will lead to an accurate spatial representation of objects under inspection and will also enable partial three-dimensional images to be formed, thus enhancing detection of concealed contraband such as explosives, weapons, narcotics and dangerous chemicals.

Impact of the research
Security Imaging is a major component of the UK Home Office ‘science and innovation strategy’ (2009-12) in preventing international crime. By supporting the development of enhanced technologies capable of providing high-quality information to screening operators, the project will directly support the needs of practitioners in charge of detecting and assessing potential threats from terrorism and organised crime. By initiating a new partnership between UCL and one of the leading organisations in the market, this proposal also contributes to UCL’s 'Sustainable Cities' Grand Challenge, in that it is concerned with the development of new measures to increase the security of our urban areas in an ethical and responsible manner. New technology is currently making a major impact in making our borders stronger and preventing terrorism. However, most imaging systems require access to both sides of the imaged vehicle/cargo.

Developing systems that could provide the ability to image in 3-D with access to only one side of an object could transform the ability to screen at entry points to the UK and within the mainland. Road-side inspections, monitoring traffic on motorways or at ports could be carried out with minimum disruption of traffic flows. Through its support of the work (including licensing of its core Background IP in the field), Rapiscan Systems shall be the route to market for the research in the security sector while UCL shall be able to exploit the results of the work in other fields. These fields might be in industrial processing, avoiding the importation of illicit drugs and in food processing.


RAPISCAN SYSTEMS have funded student Nicholas Calvert on the four-year SECReT programme, working with UCL SECReT and UCL Medical Physics and Bio-Engineering.  As the world’s leading security screening provider, Rapiscan Systems provides state of the art products, solutions and services that meet customers’ most demanding threat detection needs while improving operational efficiency.