A neutron imaging system at the Czech Technical University (CTU) in Prague reveals the world axis (a symbol connecting the material and spiritual worlds) inside a Tibetan Bon statue (Chamma). (Photo/L. Sklenka, Czech Technical University)
Neutron imaging is a non-invasive technique that uses neutron sources from research reactors or accelerators to examine internal structures. “It is a fantastic tool with unlimited potential in scientific and industrial research and development, as well as in forensics and antiquity studies,” said Molly-Kate Gavello, Deputy Director of Projects at the IAEA. Neutron imaging can be used to test motors, shock absorbers and turbine blades, to show how water flows through a living plant, or to examine the inside of a fossilized dinosaur skull filled with iron rock.
“The new sensitive detectors open up a whole new field of applications for these reactors, which cannot provide enough neutrons for complex neutron scattering experiments.”
Burkhard Schlinger, Technical University of Munich, Germany
Although neutron imaging has been used since the 1950s, two-dimensional film imaging was the main imaging method until the 1990s. With the advent of digital technology, including advanced digital cameras, neutron imaging now uses computed tomography (CT), which uses hundreds of images taken from different angles to create highly detailed three-dimensional (3D) images.
Until recently, neutron imaging using CT or 3D imaging was not feasible for low-flux neutron sources, such as low-power research reactors, for technical and financial reasons.
High-quality images at low power
This changed in 2021 when PhD student Jana Matushkova and her advisor Lubomir Sklenka at the Czech Technical University (CTU) in Prague demonstrated the ability to use CT for neutron imaging at 500 watts in a research reactor.
This breakthrough resulted from two developments. First, low-cost, high-quality astronomical cameras had become available a decade earlier. Second, researchers at the Heinz Mayer-Leibniz Research Neutron Source (FRM II) at the Technical University of Munich in Germany realized the potential of these new cameras and demonstrated the first mini-facility for neutron tomography, including at low-power reactors, in 2016. Burkhard Schlinger’s team developed and built a low-cost, high-quality neutron imaging system with 3D-printed detector housings at the FRM II research reactor, as well as a scaled-down version of specialized control software for the Advanced Neutron Tomography and Radiography Experimental System (ANTARES) facility. The image quality of the new detector is comparable to the state-of-the-art system normally used at the ANTARES facility.
Matuskova wanted to test neutron imaging with a low-power neutron source, such as the 500-watt VR-1 training reactor at the Czech Technical University, compared to the 20-MW FRM II reactor, which is 40,000 times more powerful and produces 40,000 times more neutrons than the reactor at the Czech Technical University. She faced challenges because she could not access the Czech Technical University facility to conduct experiments due to COVID-19 restrictions.
Sklenka contacted Schlinger for advice on how to replicate the low-cost system developed at FRM II, and Schlinger provided Matuskova with advice over a video call and gave her information on the system design and where to source the necessary components. Step by step, Matushkova built a neutron imaging system in her home and tested it with visible light.
After the COVID-19 restrictions were lifted, Matushkova installed her system at the Czech Technical University reactor and successfully produced the first digital neutron 2D image at the Czech Technical University, followed by neutron computed tomography imaging at 500 watts for 12 hours.
Matushkova is currently improving the neutron imaging system at the Czech Technical University as part of her doctoral research. The system is mainly used for educational purposes, but it is also used to carry out research, such as examining artifacts in cooperation with the National Gallery in Prague.
Sharing technology and expertise
The experience of the FRM II facility and the Czech Technical University shows that the micro-facility can be used for any neutron source, including very low-power research reactors. Schlinger says his team is ready to provide the design and software free of charge and to help with installation and commissioning internationally.
With parts made with 3D printers, software scaled down to fit on laptops and falling prices for astrophotography cameras, the whole set can be assembled for less than 5,000 euros and is easy to transport. In 2022, Schlinger and Aaron Kraft, a research scientist at the Idaho National Laboratory in the United States, led an IAEA expert mission to install a digital neutron imaging system at the Chilean Nuclear Energy Commission’s RECH-1 research reactor. Schlinger brought the components in a suitcase, and the system was installed in two days.
“The IAEA played a key role in making this technology available for low-power research reactors,” Schlinger said. “The new sensitive detectors open up a whole new field of applications for these reactors, which cannot provide enough neutrons for complex neutron scattering experiments. Neutron imaging makes them more accessible for education, research and collaboration with museums.”
The IAEA supports technical cooperation with research reactors, including expert missions and equipment procurement. It also publishes neutron imaging guidelines, provides regional training, and is expanding e-learning opportunities. In 2022, Matushkova spent four months at the RA-6 research reactor in Argentina, coordinated by the IAEA, helping to install and test a low-cost neutron imaging system.
A similar dual neutron-X-ray system has also been installed and commissioned at the IAEA Neutron Science Facility in Seibersdorf, Austria, and is currently being used for training.
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What is neutron imaging?
Neutron imaging is a non-invasive method for examining the internal structure and composition of opaque objects. The principle is similar to that of X-ray imaging. However, while X-rays are absorbed by dense materials such as metals, neutron beams penetrate most metals and rocks and are attenuated by some light elements such as boron, carbon, hydrogen and lithium. Neutrons also help to observe magnetic fields and strain in technical and structural materials.
