Neutron scattering: a collaborative project brings Hong Kong science to the world
The Joint Laboratory on Neutron Scattering was set up by the City University of Hong Kong and the Chinese Academy of Sciences. The Joint Laboratory is directed by Professor Wang Xunli (Croucher Senior Research Fellowship 2021) and Professor Chen Hesheng of the Chinese Academy of Sciences Institute of High Energy Physics. Wang and Chen have worked together to create a platform for collaboration on problems related to neutron scattering science and technology.
The Joint Laboratory has three long-term goals: to establish Hong Kong as an international centre of excellence in neutron scattering science and technology; to provide advice and technical support to the Chinese Academy of Sciences and to make the laboratory one of the most productive scientific facilities of its kind.
What is neutron scattering?
Neutron scattering uses the deflection of free neutrons by matter to investigate the microscopic properties of materials. It can occur naturally and has been harnessed by scientists as a technique used to study the structure and dynamics of matter at a microscopic level. It offers a significant and versatile method for characterising materials.
Neutrons possess a penetrating power that allows researchers to look within a material, for example, at how a weld is performing, without destroying the material’s fabric. By measuring the change in energy and momentum of neutrons, scientists can learn about the atomic structure and movement patterns of materials.
This research is already making contributions in the fields of medicine, new nuclear energy, nanotechnology, and physics.
Professor Wang Xunli
Professor Wang Xunli graduated from Peking University with a B.S. in Physics and went to the US as a CUSPEA scholar, receiving a PhD in Physics from Iowa State University. Prior to joining City University of Hong Kong in 2012, he had been working at Oak Ridge National Laboratory in the US, rising through the ranks to Distinguished Staff Member.
In the field of neutron scattering, Wang jokes that he has become a senior people in the science simply because so many of its pioneers have retired. During his career, Wang has rubbed shoulders with some of the truly great minds in this area of study.
“At Iowa State University I studied for six years under the great Professor Costa Stassis,” says Wang, adding that during which he spent two years at the Argonne National Laboratory in Chicago; a period he said that “had a profound influence” on him.
“Stassis’s advisor had been Cliff Shull who won the Nobel Prize in 1994 for his development work in neutron scattering,” he says. “So if you like, I’m Cliff Shull’s academic grandson.”
Wang became intrigued by neutron scattering when he began doing simple experiments at Peking University in the early 80s. “We were doing an X-ray experiment as part of a physics course measuring the lines between X-ray spectrum. By doing this we could determine the spacing between atoms,” he says.
From these relatively primitive experiments, Professor Wang has advanced his research to include investigations into a host of materials including the properties of metallic glass. This revolutionary material has a host of engineering applications, among them magnetic qualities that will assist China in a major upgrade of its electricity delivery system.
“When I first studied neutron scattering, I was really looking at more fundamental behaviours, like magnetic interactions: the interaction between magnetic moments in functional materials, like high-temperature superconductors,” he says. “But in my post-doc time, I switched to working on mechanical behaviours.”
Now his studies have broadened into engineering, looking closely at the stresses and deformation of materials – used in bridges, railways, car engines and jet engines – at an atomic level.
In a mechanical test, the material is put under stress – either pulled or crushed – and the load measured to produce a stress–strain curve; however, this kind of testing only reveals the average behaviour. But, Wang says, “It’s not that simple … materials underneath [the surface] have structures that are not uniform. They have grains with different crystallographic orientations, which have interactions between them. Some grains deform more, while others deform less. Some become plastic early, [while] others have to shoulder more of the load because other grains refuse to take on more.
“We are interested in this level of deformation behaviour because it tells us about the deformation at a microscopic level. If we can understand that then we can tune the material’s properties to control these deformation behaviours.”
An important collaboration
Critical to this work has been the collaboration between the City University of Hong Kong and the China Spallation Neutron Source, located in Dongguan, Guangdong Province.
“Neutron scattering was a fairly foreign concept in Hong Kong but it’s a very powerful technique as you can see,” says Wang.
He advised on the China Spallation Neutron Source project in Dongguan from the beginning; the facility was built starting in 2011 and opened in 2018.
“It took a long time to establish the scientific case to fund it from a financial point of view but after the decision was made it was built very quickly,” he says.
Croucher Summer Course on Neutron Scattering
Croucher Summer Courses are intensive residential courses which set out to educate and inspire highly promising postgraduate students and early career researchers from in and outside Hong Kong.
The Croucher Summer Course on Neutron Scattering was established in 2014 in anticipation of the opening of the neutron source in Dongguan.
The joint laboratory is now important as a platform for research, as well as providing critical professional training for students. Wang says the summer courses have been one of the greatest success stories of the joint project.
“A third of the students came from Hong Kong, a third from mainland China and the other third were from different regions; there were students from Cambridge and Oxford, from Tokyo and universities in Australia. The students learn from the great instructors that we have at the summer course, but they also learn from each other; there is a fantastic interaction between the students.”
The summer courses and joint laboratory have been supported by Chinese Academy of Science and Croucher Foundation since 2014. Wang says the support of the Croucher Foundation has been a key driver in making the joint project a reality.
“I’m really grateful to the Croucher Foundation, which appreciates this kind of long term work – from the very novel aspects of neutron scattering, to the facility in Dongguan and to supporting us with the summer courses,” he says.
