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Mano Raj Dhanalakshmi Veeraraj and Joan Vila-Comamala, both from the PSI Center for Photon Science, with the achromatic neutron lens outside the Swiss Spallation Neutron Source SINQ. Close collaboration between experts in neutron sciences and X-ray optics allowed a longstanding problem in neutron imaging to be overcome.
Photo Credit: © Paul Scherrer Institute PSI/Markus Fischer
Scientific Frontline: Extended "At a Glance" Summary: The Achromatic Neutron Lens
The Core Concept: The achromatic neutron lens is a novel optical device that brings a broad range of neutron wavelengths to a single focal point, allowing for sharp, magnified neutron imaging. It is the first lens of its kind to successfully focus neutrons, which are notoriously difficult to manipulate due to their weak interaction with matter.
Key Distinction/Mechanism: Unlike conventional visible-light lenses that rely solely on refraction, this device combines both refraction and diffraction. Carefully manufactured diamond structures refract the neutron beam, while precisely patterned, nanoscale concentric nickel rings generate a diffraction pattern to form a magnified, high-resolution image on a detector.
Major Frameworks/Components:
- Achromatic Focusing: The ability to align a broad spectrum of wavelengths to the same focal point without chromatic aberration.
- Neutron Diffraction: The use of concentric nickel rings, measuring well under 200 nanometers, to spread and pattern neutron waves.
- Neutron Refraction: The application of finely engineered diamond structures to bend the path of the neutron beam.
- Electron-Beam Lithography: The nanofabrication technique utilized in cleanroom facilities to create the intricate structural geometries required for the lens.
Branch of Science: Optics, Particle Physics, Condensed Matter Physics, Materials Science, and Nanofabrication.
Future Application: The lens facilitates advanced neutron microscopy and the non-destructive observation of fine internal details within running engines, operating lithium-ion batteries, living plant tissues, and intact archaeological artifacts.
Why It Matters: Previously, neutron imaging required placing samples within centimeters of a detector to maintain image sharpness, severely limiting sample size. This lens enables sub-20-micrometer resolution from up to 6 meters away, allowing scientists to monitor processes inside bulky, extreme environments like furnaces, cryostats, and pressure cells.
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| A sharper view from meters away: This magnified neutron image of a three millimeter PSI logo was acquired using the new achromatic neutron lens, with the logo placed six meters from the detector. Without the lens, comparable resolution would require the object to be placed within centimeters – or even millimeters – of the detector. Image Credit: © Paul Scherrer Institute PSI/Mano Raj Dhanalakshmi Veeraraj |
Researchers at the Paul Scherrer Institute (PSI) have developed the world’s first achromatic lens for neutron imaging. The lens overcomes a longstanding obstacle in the field: focusing neutrons of different wavelengths well enough to form a sharp, magnified image. With the lens, researchers can now image thick samples and follow processes inside bulky equipment such as furnaces, cryostats, or pressure cells.
Neutrons can provide unique insights into the structure of materials, but they are hard to manipulate. Like X-rays, neutrons—produced as a beam at research facilities such as the Swiss Spallation Neutron Source (SINQ)—are used to image inside materials and objects. Unlike X-rays, however, neutrons can penetrate deeply into many metals while remaining highly sensitive to light elements such as hydrogen and lithium. In this way, they can be used to observe oil, polymer, or lithium distribution inside dense metallic structures such as engines or batteries, reveal water uptake in plants, or nondestructively examine priceless archaeological artifacts.
Yet the same weak interaction with matter that makes neutrons such a useful tool also makes them notoriously difficult to deflect or focus—a fact that has limited the development of advanced imaging techniques. Now, PSI scientists have reported in Nature Communications a new type of lens that overcomes this barrier.
A Lens for All Colors of Neutrons
A large part of the challenge lies in the fact that neutron beams typically contain neutrons of many different wavelengths. To achieve a high-resolution image, the lens must bring these to the same focal point. Despite past attempts, no practical neutron imaging lens has been able to focus the broad range of wavelengths in a neutron beam—until now.
Currently, neutron imaging is performed without lenses, but this forces researchers to place samples close to the detector to keep images sharp. “This limits the achievable resolution, as well as the size of the object or sample environment that can be imaged,” says Mano Raj Dhanalakshmi Veeraraj, first author of the study and PhD student in the PSI Center for Photon Science.
The new lens—the first of its type in the world—is a so-called achromatic neutron lens, which focuses a broad range of neutron wavelengths to the same point. This enables sharp, magnified imaging with a resolution below 20 micrometers—even for objects that cannot be placed close to the detector.
“The lack of such a lens has held back neutron imaging for decades,” says Joan Vila-Comamala, a scientist in the PSI Center for Photon Science, who led the team. “Now that we have it, it becomes possible to follow processes inside equipment such as furnaces, cryostats, or pressure cells. It also opens the path to neutron microscopy, making it possible to produce magnified images of an object and reveal more detail.”
A Completely New Way of Acquiring Images
In the study, the researchers tested the lens by imaging a commercial lithium-ion battery. With the battery placed 6 meters away from the detector, they could magnify the layered structure of the wound electrode assembly by seven times.
In the future, this could make it possible to observe fine internal details of materials and devices while they are functioning in realistic environments, such as detecting structural changes within components of a running engine.
“This is just the beginning,” adds Dhanalakshmi Veeraraj. “We already see ways to improve the lens. The key point is not simply resolution, but a completely new way of acquiring images.”
Now, neutron imaging facilities will have to catch up. To fully exploit the new lenses, some facilities may need longer beamlines. “If you can have a long enough beamline, you can, in principle, magnify more. It is not limited by the lens, but by the length of the instrument,” says Dhanalakshmi Veeraraj. New facilities such as the European Spallation Source, currently under construction in Sweden, are already incorporating these new requirements, paving the way for further growth in neutron imaging and its applications.
Building on X-ray Lens Success
The technology draws on the team’s earlier breakthrough in X-ray optics: the development in 2022 of an achromatic X-ray lens for synchrotron and X-ray free-electron laser facilities such as the Swiss Light Source (SLS) and SwissFEL. The development of the neutron lens combined this X-ray optics expertise from the PSI Center for Photon Science with neutron imaging expertise from the PSI Center for Neutron and Muon Sciences.
The neutron lenses consist of concentric rings made of nickel and precisely shaped diamond structures, arranged in a carefully defined geometry. Unlike conventional visible-light lenses, which rely only on refraction, the neutron lenses also exploit diffraction—the phenomenon that causes waves to spread out or form patterns when passing through gratings or small apertures. The nickel rings generate the diffraction pattern, while the diamond structures refract the neutron beam; together, these effects form a magnified image on the detector.
The intricate nickel structures were fabricated using electron-beam lithography in PSI’s recently inaugurated PICO cleanroom facilities, while the diamond refractive structures were manufactured by the Swiss company SYNOVA S.A. “The nickel rings get smaller and smaller, with the finest rings measuring well below 200 nanometers,” says Vila-Comamala.
After fabrication, the prototypes could be tested rapidly with X-rays at the Swiss Light Source (SLS) and tested with neutrons at the Swiss Spallation Neutron Source (SINQ).
“There are few other places in the world, if any, where this could have happened,” says Dhanalakshmi Veeraraj. “The close collaboration between experts in neutron imaging, X-ray optics, and nanofabrication, based within walking distance of one another on the PSI campus, makes technological breakthroughs such as this possible.”
Published in journal: Nature Communications
Title: An achromatic neutron lens
Authors: Mano raj Dhanalakshmi Veeraraj, Di Qu, Hui-Yuan Chen, Silas Strebel, Peng Qi, Anna Fedrigo, Lukas Helfen, Alessandro Tengattini, Matteo Busi, Hongchang Wang, Piero Tranchida, Anders Kaestner, Christian David, Markus Strobl, and Joan Vila-Comamala
Source/Credit: Paul Scherrer Institute | Simone Pengue
Edited by: Scientific Frontline
Reference Number: phy071426_01