Inverse modeling of X-ray imaging to combat nuclear materials trafficking

May 20, 2014
Simulated inspection of a layered, baggage-like object that contains a thin, shielded plutonium wedge (a) (not to scale). A single energy radiograph is shown in (b), along with the material estimations from the adaptive inverse algorithm that indicate an equivalent of color vision (by material) for a single-view radiograph using spectral X-ray detector data.

( —As part of the ongoing effort to curtail illicit trafficking of nuclear materials, scientists from Pacific Northwest National Laboratory and the University of Texas at Austin studied inverse modeling of spectral X-ray radiography to determine the presence of nuclear materials in small containers or composite objects, such as baggage. In their examination, the researchers applied an inversion algorithm to synthetic radiographs of objects composed of layers of plutonium, cotton, steel, lead, aluminum, and copper to estimate the quantities of these materials within the layers. Their work showed that coupling the algorithm with current-generation commercial detectors has the potential to distinguish small quantities of nuclear materials from other high-Z materials, such as nuclear material stowed within airline passenger luggage.

Extending existing imaging technology to detect small amounts of plutonium or highly enriched uranium hidden in composite objects could provide a major advance in combating the threat of trafficking.

Regularized inversion techniques, such as those Andy Gilbert (the paper's lead author) applied to this problem, have proven effective in distinguishing between multiple components of a given signal in a variety of applications. Using a list of possible materials and associated X-ray attenuation profiles as basis functions that are coupled to Beer's Law as a forward model to account for attenuation by photon absorption and scattering, the inversion breaks down the overall attenuated signal in each image pixel into components from the individual materials. These components are the coefficients in the forward model, representing areal densities of materials. Importantly, the algorithm has been developed to be adaptive, requiring minimal user input if deployed. Despite complicating factors associated with imaging high-density, high-Z objects, these techniques show promise for nuclear trafficking applications. 

Building on the success of inverse modeling and using today's spectrally sensitive detectors to detect the presence of small amounts of plutonium in the simulated composite objects tested to date, the scientists are examining the model's potential to adapt and expand to high-energy X-ray systems and multiple X-ray spectra, as well as its application to verification of arms control treaty-limited items.

Explore further: Sensitive detection method may help impede illicit nuclear trafficking

More information: Gilbert AJ, BS McDonald, SM Robinson, KD Jarman, TA White, and MR Deinert. 2014. "Non-invasive material discrimination using spectral x-ray radiography." Journal of Applied Physics 115(15):154901. DOI: 10.1063/1.4870043.

add to favorites email to friend print save as pdf

Related Stories

Study cites 'dangerous weak link' in nuke security

Jan 08, 2014

The number of countries possessing the makings of a nuclear bomb has dropped by almost one-quarter over the past two years, but there remain "dangerous weak links" in nuclear materials security that could be exploited by ...

Researchers model spent nuclear fuels

Mar 21, 2014

( —Lawrence Livermore scientists have modeled actinide-based alloys, such as spent nuclear fuel, in an effort to predict the impact of evolving fuel chemistry on material performance.

Recommended for you

Synchrotron upgrade to make X-rays even brighter

1 hour ago

( —The X-rays produced by the Cornell High Energy Synchrotron Source (CHESS) are bright, but they will soon be even brighter, thanks to a major upgrade that will make the quality of CHESS' X-rays ...

Cold Atom Laboratory creates atomic dance

16 hours ago

Like dancers in a chorus line, atoms' movements become synchronized when lowered to extremely cold temperatures. To study this bizarre phenomenon, called a Bose-Einstein condensate, researchers need to cool ...

Scientists create possible precursor to life

Oct 20, 2014

How did life originate? And can scientists create life? These questions not only occupy the minds of scientists interested in the origin of life, but also researchers working with technology of the future. ...

Superconducting circuits, simplified

Oct 17, 2014

Computer chips with superconducting circuits—circuits with zero electrical resistance—would be 50 to 100 times as energy-efficient as today's chips, an attractive trait given the increasing power consumption ...

User comments : 0