18 August 2021

Particle physics at ports: Using muon tomography to keep cargo secure

Particle physicists are primarily concerned with untangling the Universe at the most fundamental level, more often than you might think, the discoveries they make can also help solve some of the most practical problems here on Earth.

Shipping containers at a port

Particle physics tackles some of the biggest questions: What is the Universe made of? What are the rules that govern it? This quest to understand the laws of nature, and our place within it, is central to the scientific mission that has driven humanity for millenia. But while particle physicists are primarily concerned with untangling the Universe at the most fundamental level, more often than you might think, the discoveries they make can also help solve some of the most practical problems here on Earth.

The study of muons is a good example. These subatomic particles are similar to electrons but with a greater mass, and were first discovered by researchers at the California Institute of Technology in 1936. Every minute, thousands of muons hit every square metre of the Earth’s surface as a result of cosmic ray collisions occurring in our planet’s atmosphere. They have been observed in the atmosphere and deep beneath the ground. The properties of muons, including the probability that they will collide with atoms and their resulting deflection, have been determined by multiple measurements and calculations.

Muons are dangerous for high sensitivity experiments conducted in underground laboratories as they, or the products of their collisions with atoms, can mimic the signals that scientists expect to see from various phenomena beyond the Standard Model of particle physics – dark matter, proton decay, non-standard processes involving neutrinos. But the known properties of muons, and their collisions with atoms, can provide important insights into the materials that different objects are made of.

This is the essence of muon tomography: in effect, using muons to visualise the internal layout of physical structures, in much the same way that X-rays are used to image the human skeleton. Famous experiments were performed in the 1960s to try and use muon tomography to detect previously undiscovered cavities in the pyramids of Giza, Egypt – although in that instance, none were found.

Professor Vitaly Kudryavtsev, a particle physicist at the University of Sheffield, began studying muons in 2006 but had doubts about how widely muon tomography could be applied. “I was sceptical,” he said, “but I began helping collaborators run the code on muon tomography experiments and got results.” Spurred on by some promising collaborations, Vitaly invited undergraduate students to work with him on muon tomography for their final year research projects. Eventually, two PhD students specialising in muon tomography joined Vitaly’s research group and publications followed, adding to the body of evidence that muon tomography could help solve a wide variety of problems outside the lab.

From pyramids and volcanoes to ports and railways

Muon tomography has received a significant boost in recent years, as it has been used to detect a long cavity in Giza's Great Pyramid and map several volcanoes. “That proved the technology worked,” said Vitaly, who has now worked on muon tomography applications ranging from carbon capture and storage to volcanoes in the Andes.

The context for the latest project Vitaly has joined may appear less exotic than Egyptian deserts and South American mountain ranges. But as global shipping infrastructure has been rocked by the coronavirus pandemic and a realignment of the politics around free trade, it could have an impact around the world.

I was sceptical, but I began helping collaborators run the code on muon tomography experiments and got results.

Professor Vitaly Kudryavtsev

University of Sheffield

He is working with a number of universities, research institutions, industrial companies and border agencies to develop muon tomography technology that can identify different materials at border checkpoints. This new consortium, led by researchers at the University of Tartu in Estonia and start-up company GScan OÜ, has been backed by a €7.5 million grant through the European Commission’s Horizon 2020 programme. Support has also come to Sheffield through the Science and Technology Facilities Council’s Impact Acceleration Accounts scheme.

Another muon tomography project at the University of Sheffield has resulted in a new start-up company. Professor Lee Thompson started building muon detectors to use in demonstrations when teaching physics to schoolchildren. In recent years he has contributed to CHANCE, a Horizon 2020 project that uses muon tomography in nuclear waste disposal. He is now also Technical Director of Geoptic, a spin-out from Sheffield, the University of Durham, and St Mary’s University, Twickenham.

Geoptic uses instruments, similar to the ones Lee first used in the classroom, to scan railway tunnels that could be overburdened and at risk of collapse. This technology means that tunnels do not need to be drilled into to assess their structural integrity, making the process safer and more efficient. The Institute of Physics awarded a Business Start-Up prize to Geoptic for the contributions it has already made to the rail industry.

Bringing laboratory science to society

The consortium Vitaly has joined is equally tuned into the concerns of industry, and is all about increasing security across global supply chains without compromising on efficiency. Currently, only a fraction of the vehicles arriving at border checkpoints are scanned to verify their contents because no technology exists to do so quickly, cheaply and at a large scale. The goal of the consortium is to build, over the next four years, a prototype scanner which can do just that, and complement existing methods of cargo scanning. By using muon tomography, the team hopes their device will also be safer and easier to use than the X-ray technology used to scan luggage at airports.

This is the world’s most innovative development project in the field of customs control technology in the last decade.

Ants Kutti

Estonian Tax and Customs Board

“I’ve been talking to our partners about how cargo can be scanned at ports,” Vitaly explains. “In general, scanning time is a big issue, so the questions are how fast the technology will work to do the scanning, and how long the analysis will take to identify the contents of the cargo.”

Partners on the project have high hopes that the project can make customs controls faster and more efficient. Ants Kutti from the Estonian Tax and Customs Board, a consortium member, said: “This is the world’s most innovative development project in the field of customs control technology in the last decade.”

Project co-ordinator Professor Gholamreza Anbarjafari from the University of Tartu added: “The project is a good example of a long and fruitful collaboration between a university and start-ups that brings laboratory science to society.”

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