Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Movable silicon 'lenses' enable neutrons to see new range of details inside objects


You can't see well without lenses that can focus, whether those lenses are in your eye or the microscope you peer through. An innovative new way to focus beams of neutrons might allow scientists to probe the interiors of opaque objects at a size range they were blind to previously, allowing them to explore the innards of objects from meteorites to cutting-edge manufactured materials without damaging them.

The method, published today in Physical Review Letters, could convert what historically has been a support tool for neutron science into a full-fledged scanning technique that could reveal details ranging in size from 1 nanometer up to 10 micrometers within larger objects.

The neutron interferometer can scan the interior of thick objects, such as this chunk of granite, providing enough detail to show the four types of rock that are mixed within it.

Credit: Huber & Hanacek, NIST

Moving these three gratings focuses neutron beams on a sample, allowing them to perceive interior details ranging in size from 1 nanometer to 10 micrometers.

Credit: Huber & Hanacek, NIST

The approach provides this tool, known as neutron interferometry, with what are essentially its first movable "lenses" capable of zooming in and out on details in this size range -- a range that has been difficult to probe, even with other neutron scanning methods.

More precisely, these "lenses" are silicon wafers acting as diffraction gratings, which take advantage of neutrons' wavelike properties. The gratings split and redirect a neutron beam so that the waves bounce off an object's edges and then collide with one another, creating a visible moiré interference pattern representative of the object that is easy for experts to interpret.

The method was developed by a team of researchers from the National Institute of Standards and Technology (NIST), the National Institutes of Health (NIH), and Canada's University of Waterloo. According to NIST's Michael Huber, the approach could make neutron interferometry into one of the best exploratory tools in a material scientist's kit.

"We can look at structure on lots of different levels and at different scales," said Huber, a physicist with NIST's Physical Measurement Laboratory who conducts experiments at the NIST Center for Neutron Research (NCNR). "It could complement other scanning techniques because its resolution is so good. It has a dramatic ability to focus, and we aren't limited to looking at thin slices of material as with other methods--we can easily look inside a thick chunk of rock."

Interferometry is a specialty in the world of neutron science. Before scientists can probe an object's interior with a neutron beam, they must first possess a few fundamental details about how the neutrons will bounce off the object's atomic structure. One of those details is a substance's index of refraction, a number indicating how much it will bend the beam from the direction it is traveling. (Water bends light in a related fashion--that's why your arm looks like it bends away when you dip it into a swimming pool.) Neutron interferometry is the best way to obtain that crucial measurement.

Neutron interferometry also has potential for other uses in fundamental physics, such as accurately measuring the gravitational constant. It's sensitive enough to detect how an object's gravitational force can deflect neutrons, just as the Earth attracts a flying ball (and vice versa). But the neutron method's Achilles' heel has been how slowly it works. To focus neutrons on a sample of material, an interferometer has needed a crystal carved to precise dimensions out of a single large block of expensive, top-quality silicon. (Other neutron techniques can make do with crystals of far lower quality.)

Unfortunately, crystals that are good enough for interferometry also block out most of the neutrons that strike them, meaning it takes a long time for a beam to send enough neutrons past a sample to get an accurate index of refraction. Other tasks would take far longer.

"The neutron sources are already very weak," said Waterloo's Dmitry Pushin. "It would take a hundred years to get a good answer to fundamental questions such as the value of the gravitational constant."

The new approach sidesteps these problems by using a trio of thin silicon gratings to focus the neutrons instead of a single costly crystal. Under a microscope, the flat surface of each grating looks like a comb with narrow, closely spaced teeth. Not only do the gratings allow the entire neutron beam to pass through them--rather than the trickle of neutrons that get through the crystal--they have the pivotal advantage of being movable.

"You focus by moving the grating a fraction of a millimeter," Huber said. "It's slight but not difficult."

Demonstrated at the NIST Center for Neutron Research, the team's approach builds on a discovery initially made at NIH, where scientists were experimenting with applying the gratings to X-ray beams and noticed a moiré pattern forming on their visual imager.

"The idea was first developed by our lab to capture the image of materials where X-rays travel at slightly different speeds than in the air, such as the human body itself," said Han Wen, senior investigator at NIH's National Heart, Lung, and Blood Institute. "Central to this idea is X-ray gratings, which were made with the highly specialized tools at the NIST Nanofab facility."

Fortuitously, the NIST and Waterloo scientists met the NIH team members at a conference and struck up a collaboration, suspecting that the gratings would work just as well for neutrons as for X-rays. The NIH team brought the gratings back to NIST, where they were assembled into the neutron interferometer.

After equally good results at the NCNR, Huber said only one thing stands in the way of their interferometer becoming a great tool for industry: They need a set of apertures of different widths the neutron beam will pass through before it hits the interferometer. Right now, they only have a single aperture at their disposal, and it limits their vision.

"We can see the full range of 1 nanometers to 10 micrometers now, but the image is kind of blurry because we don't get enough data," he said. "Every different aperture gives us another data point, and with enough points we can start doing quantitative analysis of a material's microstructure. We're hoping that we can get a set of maybe a hundred made, which would enable us to get detailed quantitative information."

The team has already scanned the interior of a block of granite that contains a mixture of four different minerals, and the scan shows the details of where each bit of mineral sits. Huber said the method would be good for non-invasive scans of porous objects like meteorites or manufactured materials, such as gels or foams, which are the basis of many consumer products.

"We're also hoping we can finally do that gravitational constant measurement," he said. "We could put a big block of some heavy metal like tungsten nearby and see how it bends the beam. It would improve our understanding of the universe and wouldn't take longer than our lifetimes."

Media Contact

Chad Boutin


Chad Boutin | EurekAlert!

Further reports about: NIH NIST Neutron Neutron Research X-rays gravitational lenses micrometers

More articles from Physics and Astronomy:

nachricht Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1
21.03.2018 | Fraunhofer-Institut für Hochfrequenzphysik und Radartechnik FHR

nachricht Taming chaos: Calculating probability in complex systems
21.03.2018 | American Institute of Physics

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

TRAPPIST-1 planets provide clues to the nature of habitable worlds

21.03.2018 | Physics and Astronomy

The search for dark matter widens

21.03.2018 | Materials Sciences

Natural enemies reduce pesticide use

21.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>