NTU scientists first to prove quantum theory in giant leap for precise X-ray imaging
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Nanyang Technological University's Nanyang Assistant Professor Wong Liang Jie (left) and research fellow Huang Sunchao loading a sample into a scanning electron microscope used in their quantum recoil experiments.
PHOTO: NTU
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SINGAPORE – A team of seven scientists from Nanyang Technological University (NTU) is the first in the world to demonstrate an 83-year-old quantum physics theory, in a breakthrough that will pave the way for more precise X-ray imaging.
The team, led by NTU’s Nanyang Assistant Professor Wong Liang Jie from the School of Electrical and Electronic Engineering, successfully showed in experiments that X-rays are emitted at lower energy levels, as predicted by quantum recoil theory, when charged particles such as electrons pass through a material to produce radiation.
Harnessing quantum recoil, which has eluded scientists for decades, will enable more precise X-ray machines to be developed for imaging human tissue samples and detecting flaws in semiconductor chips.
Radiation such as X-rays can be produced when electrically charged particles such as electrons are accelerated to increase their energy, and passed through a material, disturbing its atoms. As the atoms settle back into their original states, radiation is emitted.
Russian physicist Vitaly Ginzburg hypothesised in 1940 that the energy of the radiation would be lower than what is predicted by classical physics.
This would happen as a result of electrons slowing down and getting deflected as they interact with the atoms of the material they pass through.
This phenomenon is known as “quantum recoil”.
Classical physics assumes that the changes to the electrons’ energy and path as they interact with the atoms are negligible, and thus have an insignificant impact on the energy of the radiation produced.
Proving quantum recoil had frustrated scientists for decades.
Special materials, such as those with repeated patterns in their atomic structures, were required – but the precision required to create them had been limited by the technology available.
The NTU team, which had already been researching the production of X-rays by exposing inorganic compounds about the size of computer chips to moving electrons, turned their experiments to quantum recoil.
With a scanning electron microscope, they bombarded separate samples of graphite and hexagonal boron nitride (h-BN) with electrons.
The energies of the X-rays emitted were measured and found to match the values predicted by quantum recoil theory.
A scanning electron microscope used in Nanyang Technological University’s quantum recoil experiments.
PHOTO: NTU
“It was a happy accident as we were already working with X-rays to develop a more compact way to tune and generate X-rays of different energies for medical, industrial and security applications,” Prof Wong told The Straits Times.
This meant that the team was aware of the unique properties of materials such as graphite and h-BN.
Graphite is a form of carbon used in pencil lead, while h-BN is frequently used to make lubricants in paints.
Both compounds have closely packed layers of atoms in repeating patterns, where each layer is a single atom thick.
“We put two and two together and realised that we could use these materials in experiments to demonstrate quantum recoil.”
The team found that quantum recoil and the resulting radiation energy can be modified by tweaking the electron energy, the atomic composition and the tilt angle of the material.
Building upon their previous work, the researchers developed a way to enable the same X-ray machine to generate X-rays of specific energy levels to identify human tissues more accurately.
The team is working with Singapore biomedical equipment manufacturing company CTmetrix to develop more compact and precise tunable biomedical X-ray machines. They aim to have a prototype ready by the end of 2023.
Dr Edward Morton, chief technology officer of CTmetrix, said: “We are investing in a practical demonstration system, based on the quantum recoil phenomenon, to solve problems in biomedical imaging. When our product is ready, this will support the global bioscience industry in understanding disease and the impact of medical treatments.”
Singapore company Component Technology is also looking to tap the NTU team’s technology to develop tunable X-ray inspection machines to check semiconductor chips for defects such as voids, or air pockets that can lead to chip failure.
