NIST's curved neutron beams could deliver benefits straight to industry

(Press-News.org) In a physics first, a team including scientists from the National Institute of Standards and Technology (NIST) has created a way to make beams of neutrons travel in curves. These Airy beams (named for English scientist George Airy), which the team created using a custom-built device, could enhance neutrons’ ability to reveal useful information about materials ranging from pharmaceuticals to perfumes to pesticides — in part because the beams can bend around obstacles. 

A paper announcing the findings appears in today’s issue of Physical Review Letters. The team was led by the University of Buffalo’s Dusan Sarenac, and coauthors from the Institute for Quantum Computing (IQC) at the University of Waterloo in Canada built the custom device that helped create the Airy beam. The team also includes scientists from the University of Maryland, Oak Ridge National Laboratory, Switzerland’s Paul Scherrer Institut, and Germany’s Jülich Center for Neutron Science at Heinz Maier-Leibnitz Zentrum. 

In addition to following parabola-shaped paths, Airy beams behave in other ways that can defy intuition. Unlike a typical flashlight beam, they do not spread out as they travel. They even have the capability of “self-healing,” meaning that if an obstacle blocks part of the beam, the rest of the beam regenerates its original shape after passing the obstacle.

While other research teams have created Airy beams out of other particles — such as photons or electrons — wrangling neutrons into Airy beams is more difficult. Lenses are powerless to bend them, and because neutrons have no charge, electric fields do not affect them. The team needed a new approach.

So the researchers custom-built a diffraction grating array — a square of silicon about the size of a pencil eraser’s head and scored with tiny lines. These lines, arranged into more than six million squares one micrometer across and separated at precise distances from one another, can split an ordinary beam of neutrons into an Airy beam. 

While the idea of scratching up a piece of silicon is simple in principle, figuring out just how to arrange the scratches to produce the Airy beam was anything but. 

“It took us years of work to figure out the correct dimensions for the array,” said coauthor Dmitry Pushin, IQC faculty and professor at the University of Waterloo. “We only needed about 48 hours to carve the grating at the University of Waterloo’s nanofabrication facility, but before that it took years of a postdoctoral fellow’s time to prepare.”

Neutron Airy beams could help neutron imaging facilities see better, Huber said. They would help increase the resolution of a scan or create different focal spots to look more closely at particular parts of objects, improving commonly used imaging techniques such as neutron scattering and neutron diffraction. 

One of the most tantalizing possibilities, Huber said, would be to find ways to combine a neutron Airy beam with another type of neutron beam.

“We think combining neutron beams could expand the Airy beams’ usefulness,” said Sarenac. “If someone wants Airy beams tailored for some physics or material application, they can tweak our techniques and get them.”

For example, scientists might combine a neutron Airy beam with a helical wave of neutrons, which the team learned to create a decade ago. Superimposing the two beams would allow scientists to explore a material’s chirality — a characteristic often described as “handedness,” where a molecule has two mirror-image forms that can have dramatically different properties.

A better way to explore and characterize chirality could facilitate the development of chiral molecules with specific properties and functions, potentially revolutionizing industries such as pharmaceuticals, materials science and chemical manufacturing. The global market for chiral drugs, for example, exceeds $200 billion annually, and chiral catalysis techniques underpin the manufacture of many chemical products. 

Chirality is also growing in importance for quantum computing and other cutting-edge electronic applications such as spintronics. 

“A material’s chirality can influence how electrons spin, and we could use spin-polarized electrons for information storage and processing,” Huber said. “Controlling it could also help us manipulate the qubits that form the building blocks of quantum computers. Neutron Airy beams could help us explore materials with these capabilities far more effectively.”

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