Electronic chips are made using photolithography, which involves shining ultraviolet light through a patterned mask and onto a semiconductor wafer. The light activates a photoresist on the surface, which allows the etching of a pattern on the wafer. Through successive iterations of photolithography and the deposition of metals, devices with features as small as a few dozen nanometres are created.

Crucial to this complex manufacturing process is aligning the wafer with successive masks. This must be done in a rapid and repeatable manner, while maintaining  nanometre precision throughout the manufacturing process. That’s where Queensgate – part of precision optical and mechanical instrumentation manufacturer Prior Scientific – comes into the picture.

For 45 years, UK-based Queensgate has led the way in the development of nanopositioning technologies. The firm spun out of Imperial College London in 1979 as a supplier of precision instrumentation for astronomy. Its global reputation was sealed when NASA chose Queensgate technology for use on the Space Shuttle and the International Space Station. The company has worked for over two decades with the hard-disk drive-maker Seagate to develop technologies for the rapid inspection of read/write heads during manufacture.  Queensgate is also involved in a longstanding collaboration with the UK’s National Physical Laboratory (NPL) to develop nanopositioning technologies that are being used to define international standards of measurement.

Move to larger wafers

The semiconductor industry is in the process of moving from 200 mm to 300 mm wafers – which doubles the number of chips that can be produced from a wafer. Processing the larger and heavier wafers requires a new generation of equipment that can position wafers at nanometre precision.

Queensgate already works with original equipment manufacturers (OEMs) to make optical wafer-inspection systems that are used to identify defects during the processing of 300 mm wafers. Now the company has set its sights on wafer alignment systems. The move to 300 mm wafers offers the company an opportunity to contribute to the development the next-generation alignment systems – says Queensgate product manager Craig Goodman.

“The wafers are getting bigger, which puts a bigger strain on the positioning requirements and we’re here to help solve problems that that’s causing,” explains Goodman. “We are getting lots of inquiries from OEMs about how our technology can be used in the precision positioning of wafers used to produce next-generation high-performance semiconductor devices”.

The move to 300 mm means that fabs need to align wafers that are both larger in area and much heavier. What is more, a much heavier chuck is required to hold a 300 mm wafer during production. This leads to conflicting requirements for a positioning system. It must be accurate over shorter distances as feature sizes shrink, but also be capable of moving a much larger and much heavier wafer and chuck. Today, Queensgate’s wafer stage can handle wafers weighing up to 14 kg while achieving a spatial resolution of 1.5 nm.

Goodman explains that Queensgate’s technology is not used to make large adjustments in the relative alignment of wafer and mask – which is done by longer travel stages using technologies such as air-bearings. Instead, the firm’s nanopositioning systems are used in the final stage of alignment, moving the wafer by less than 1 mm at nanometre precision.

Eliminating noise

Achieving this precision was a huge challenge that Queensgate has overcome by focusing on the sources of noise in its nanopositioning systems. Goodman says that there are two main types of noise that must be minimized. One is external vibration, which can come from a range of environmental sources – even human voices. The other is noise in the electronics that control the nanopositioning system’s piezoelectric actuators.

Goodman explains that noise reduction is achieved through the clever design of the mechanical and electronic systems used for nanopositioning. The positioning stage, for example, must be stiff to reject vibrational noise and notch filters are used to minimize the effect of electronic noise to the sub-nanometre level.

Queensgate provides its nanopostioning technology to OEMs, who integrate it within their products – which are then sold to chipmakers. Goodman says that Queensgate works in-house with its OEM customers to ensure that the desired specifications are achieved. “A stage or a positioner for 300 mm wafers is a highly customized application of our technologies,” he explains.

While the resulting nanopositioning systems are state of the art, Goodman points out that they will be used in huge facilities that process tens of thousands of wafers per month. “It is our aim and our customer’s aim that Queensgate nanopositioning technologies will be used in the mass manufacture of chips,” says Goodman. This means that the system must be very fast to achieve high throughput. “That is why we are using piezoelectric actuators for the final micron of positioning – they are very fast and very precise.”

Today most chip manufacturing is done in Asia, but there are ongoing efforts to boost production in the US and Europe to ensure secure supplies in the future. Goodman says this trend to semiconductor independence is an important opportunity for Queensgate. “It’s a highly competitive, growing and interesting market to be a part of,” he says.

• The datasheet for Queensgate’s NPS-XYP-250Q 300 mm wafer–mask alignment stage is now available. Goodman describes it as, “the physically ‘largest’ piezo nanopositioning stage ever delivered”.

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On Christmas Day in 1741, when Swedish scientist Anders Celsius first noted down the temperature in his Uppsala observatory using his own 100-point – or “Centi-grade” – scale, he would have had no idea that this was to be his greatest legacy.

A newly published, engrossing biography – Celsius: a Life and Death by Degrees  – by Ian Hembrow, tells the life story of the man whose name is so well known. The book reveals the broader scope of Celsius’ scientific contributions beyond the famous centigrade scale, as well as highlighting the collaborative nature of scientific endeavours, and drawing parallels to modern scientific challenges such as climate change.

That winter, Celsius, who was at the time in his early 40s, was making repeated measurements of the period of a pendulum – the time it takes for one complete swing back and forth. He could use that to calculate a precise value for the acceleration caused by gravity, and he was expecting to find that value to be very slightly greater in Sweden than at more southern latitudes. That would provide further evidence for the flattening of the Earth at the poles, something that Celsius had already helped establish. But it required great precision in the experimental work, and Celsius was worried that the length (and therefore the period) of the pendulum would vary slightly with temperature. He had started these measurements that summer and now it was winter, which meant he had lit a fire to hopefully match the summer temperatures. But would that suffice?

Throughout his career, Celsius had been a champion of precise measurement, and he knew that temperature readings were often far from precise. He was using a thermometer sent to him by the French astronomer Joseph-Nicolas Delisle, with a design based on the expansion of mercury. That method was promising, but Delisle used a scale that took the boiling point of water and the temperature in the basement of his home in Paris as its two  reference points. Celsius was unconvinced by the latter. So he made adaptations (which are still there to be seen in an Uppsala museum), twisting wire around the glass tube at the boiling and freezing points of water, and dividing the length between the two into 100 even steps.

The centigrade scale, later renamed in his honour, was born. In his first recorded readings he found the temperature in the pleasantly heated room to be a little over 80 degrees! Following Delisle’s system – perhaps noting that this would mean he had to do less work with negative numbers – he placed the boiling point at zero on his scale, and the freezing point at 100. It was some years later, after his death, that a scientific consensus flipped the scale on its head to create the version we know so well today.

Hembrow does a great job at placing this moment in the context of the time, and within the context of Celsius’ life. He spends considerable time recounting the scientist’s many other achievements and the milestones of his fascinating life.

The expedition that had established the flattening of the Earth at the poles was the culmination of a four-year grand tour that Celsius had undertaken in his early 30s. Already a professor at Uppsala University, in the town where he had grown up in an academic family, he travelled to Germany, Italy, France and London. There he saw at first hand the great observatories that he had heard of and established links with the people who had built and maintained them.

On his extended travels he became a respected figure in the world of science and so it was no surprise when he was selected to join a French expedition to the Arctic in 1736, led by mathematician Pierre Louis Maupertuis, to measure a degree of latitude. Issac Newton had died just a few years before and his ideas relating to gravitation were not yet universally accepted. If it could be shown that the distance between two lines of latitude was greater near the poles than on the equator, that would prove Newton right about the shape of the Earth, a key prediction of his theory of gravitation.

After a period of time in London equipping themselves with the precision instruments, the team started the arduous journey to the Far North. Once there they had to survey the land – a task made challenging by the thick forest and hilly territory. They selected nine mountains to climb with their heavy equipment, felling dozens of trees on each and then creating a sturdy wooden marker on each peak. This allowed them to create a network of triangles stretching north, with each point visible from the two next to it. But they also needed one straight line of known length to complete their calculations. With his local knowledge, Celsius knew that this could only be achieved on the frozen surface of the Torne river – and that it would involve several weeks of living on the ice, working largely in the dark and the intense cold, and sleeping in tents.

After months of hardship, the calculations were complete and showed that the length of one degree of latitude in the Arctic was almost 1.5 km longer than the equivalent value in France. The spheroid shape of the Earth had been established.

Of course, not everybody accepted the result. Politics and personalities got in the way. Hembrow uses this as the starting point for a polemic about aspects of modern science and climate change with which he ends his fine book. He argues that the painstaking work carried out by an international team, willing to share ideas and learn from each other, provides us with a template by which modern problems must be addressed.

Considering how often we use his name, most of us know little about Celsius. This book helps to address that deficit. It is a very enjoyable and accessible read and would appeal, I think, to anybody with an interest in the history of science.

• 2024 History Press 304pp £25hb

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For decades, the screwworm was eliminated in North America, but containment efforts in Panama have failed. Now cattle smugglers are helping the parasite advance north.

The technology searches for buried objects by sending vibrations into the ground and measuring what comes back.

A new transistor made from semiconducting vertical nanowires of gallium antimonide (GaSb) and indium arsenide (InAs) could rival today’s best silicon-based devices. The new transistors are switched on and off by electrons tunnelling through an energy barrier, making them highly energy-efficient. According to their developers at the Massachusetts Institute of Technology (MIT) in the US, they could be ideal for low-energy applications such as the Internet of Things (IoT).

Electronic transistors use an applied voltage to regulate the flow of electricity – that is, electrons – within a semiconductor chip. When this voltage is applied to a conventional silicon transistor, electrons climb over an energy barrier from one side of the device to the other, and it switches from an “off” state to an “on” one. This type of switching is the basis of modern information technology, but there is a fundamental physical limit on the threshold voltage required to get the electrons moving. This limit, which is sometimes termed the “Boltzmann tyranny” because it stems from the Boltzmann-like energy distribution of electrons in a semiconductor, puts a cap on the energy efficiency of this type of transistor.

Highly precise process

In the new work, MIT researchers led by electrical engineer Jesús A del Alamo made their transistor using a top-down fabrication technique they developed. This extremely precise process uses high-quality, epitaxially-grown structures and both dry and wet etching to fabricate nanowires just 6 nm in diameter. The researchers then placed a gate stack composed of a very thin gate dielectric and a metal gate on the sidewalls of the nanowires. Finally, they added point contacts to the source, gate and drain of the transistors using multiple planarization and etch-back steps.

The sub-10 nm size of the devices and the extreme thinness of the gate dielectric (just 2.4 nm) means that electrons are confined in a space so small that they can no longer move freely. In this quantum confinement regime, electrons no longer climb over the thin energy barrier at the GaSb/InAs heterojunction. Instead, they tunnel through it. The voltage required for such a device to switch is much lower than it is for traditional silicon-based transistors.

Steep switching slope and high drive current

Researchers have been studying tunnelling-type transistors for more than 20 years, notes Yanjie Shao, a postdoctoral researcher in nanoelectronics and semiconductor physics at MIT and the lead author of a study in Nature Electronics on the new transistor. Such devices are considered attractive because they allow for ultra-low-power electronics. However, they come with a major challenge: it is hard to maintain a sharp transition between “off” and “on” while delivering a high drive current.

When the project began five years ago, Shao says the team “believed in the potential of the GaSb/InAs ‘broken-band’ system to overcome this difficulty”. But it wasn’t all plain sailing. Fabricating such small vertical nanowires was, he says, “one of the biggest problems we faced”. Making a high-quality gate stack with a very low density of electronic trap states (states within dielectric materials that capture and release charge carriers in a semiconductor channel) was another challenge.

After many unsuccessful attempts, the team found a way to make the system work. “We devised a plasma-enhanced deposition method to make the gate electric and this was key to obtaining exciting transistor performance,” Shao tells Physics World.

The researchers also needed to understand the behaviour of tunnelling transistors, which Shao calls “not easy”. The task was made possible, he adds, by a combination of experimental work and first-principles modelling by Ju Li’s group at MIT, together with quantum transport simulation by David Esseni’s group at the University of Udine, Italy. These studies revealed that band alignment and near-periphery scaling of the number of conduction modes at the heterojunction interface play key roles in the physics of electrons under extreme confinement.

The reward for all this work is a device with a drive current as high as 300 uA/m and a switching slope less than 60 mV/decade (a decade, in this context, is a power of 10 difference between off and on states), meaning that the supply voltage is just 0.3 V. This is below the fundamental limit achievable with silicon-based devices, and around 20 times better than other tunnelling transistors of its type.

Potential for novel devices

Shao says the most likely applications for the new transistor are in ultra-low-voltage electronics. These will be useful for artificial intelligence and Internet of Things (IoT) applications, which require devices with higher energy efficiencies. Shao also hopes the team’s work will bring about a better understanding of the physics at surfaces and interfaces that feature extreme quantum confinement – something that could lead to novel devices that benefit from such nanoscale physics.

The MIT team is now developing transistors with a slightly different configuration that features vertical “nano-fins”. These could make it possible to build more uniform devices with less structural variation across the surface. “Being so small, even a variation of just 1 nm can adversely affect their operation,” Shao says. “We also hope that we can bring this technology closer to real manufacturing by optimizing the process technology.”

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Physical exercise plays an important role in controlling disease, including cancer, due to its effect on the human body’s immune system. A research team from the USA and India has now developed a mathematical model to quantitatively investigate the complex relationship between exercise, immune function and cancer.

Exercise is thought to supress tumour growth by activating the body’s natural killer (NK) cells. In particular, skeletal muscle contractions drive the release of interleukin-6 (IL-6), which causes NK cells to shift from an inactive to an active state. The activated NK cells can then infiltrate and kill tumour cells. To investigate this process in more depth, the team developed a mathematical model describing the transition of a NK cell from its inactive to active state, at a rate driven by exercise-induced IL-6 levels.

“We developed this model to study how the interplay of exercise intensity and exercise duration can lead to tumour suppression and how the parameters associated with these exercise features can be tuned to get optimal suppression,” explains senior author Niraj Kumar from the University of Massachusetts Boston.

Impact of exercise intensity and duration

The model, reported in Physical Biology, is constructed from three ordinary differential equations that describe the temporal evolution of the number of inactive NK cells, active NK cells and tumour cells, as functions of the growth rates, death rates, switching rates (for NK cells) and the rate of tumour cell kill by activated NK cells.

Kumar and collaborators – Jay Taylor at Northeastern University and T Bagarti at Tata Steel’s Graphene Center – first investigated how exercise intensity impacts tumour suppression. They used their model to determine the evolution over time of tumour cells for different values of α₀ – a parameter that correlates with the maximum level of IL-6 and increases with increased exercise intensity.

Simulating tumour growth over 20 days showed that the tumour population increased non-monotonically, exhibiting a minimum population (maximum tumour suppression) at a certain critical time before increasing and then reaching a steady-state value in the long term. At all time points, the largest tumour population was seen for the no-exercise case, confirming the premise that exercise helps suppress tumour growth.

The model revealed that as the intensity of the exercise increased, the level of tumour suppression increased alongside, due to the larger number of active NK cells. In addition, greater exercise intensity sustained tumour suppression for a longer time. The researchers also observed that if the initial tumour population was closer to the steady state, the effect of exercise on tumour suppression was reduced.

Next, the team examined the effect of exercise duration, by calculating tumour evolution over time for varying exercise time scales. Again, the tumour population showed non-monotonic growth with a minimum population at a certain critical time and a maximum population in the no-exercise case.  The maximum level of tumour suppression increased with increasing exercise duration.

Finally, the researchers analysed how multiple bouts of exercise impact tumour suppression, modelling a series of alternating exercise and rest periods. The model revealed that the effect of exercise on maximum tumour suppression exhibits a threshold response with exercise frequency. Up to a critical frequency, which varies with exercise intensity, the maximum tumour suppression doesn’t change. However, if the exercise frequency exceeds the critical frequency, it leads to a corresponding increase in maximum tumour suppression.

Clinical potential

Overall, the model demonstrated that increasing the intensity or duration of exercise leads to greater and sustained tumour suppression. It also showed that manipulating exercise frequency and intensity within multiple exercise bouts had a pronounced effect on tumour evolution.

These results highlight the model’s potential to guide the integration of exercise into a patient’s cancer treatment programme. While still at the early development stage, the model offers valuable insight into how exercise can influence immune responses. And as Taylor points out, as more experimental data become available, the model has potential for further extension.

“In the future, the model could be adapted for clinical use by testing its predictions in human trials,” he explains. “For now, it provides a foundation for designing exercise regimens that could optimize immune function and tumour suppression in cancer patients, based on the exercise intensity and duration.”

Next, the researchers plan to extend the model to incorporate both exercise and chemotherapy dosing. They will also explore how heterogeneity in the tumour population can influence tumour suppression.

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The US Department of Energy (DOE) has awarded $50m to a consortium of national laboratories and universities to develop sodium-ion batteries as a sustainable, low-cost alternative to lithium-ion technology.

Lithium-ion batteries currently dominate the electric-vehicle market and they are also used in smartphones and to store energy from renewable source such as wind and solar. Yet relying on a single battery technology such as lithium-ion creates dependencies on critical elements such as lithium, cobalt and nickel.

Sodium, however, is an abundant, inexpensive element and offers a promising way to diversify battery materials. The downside is that sodium-ion batteries currently store less energy per unit weight and volume than lithium-ion batteries.

The money from the DOE over the next five years will be used to create the Low-cost Earth-abundant Na-ion Storage (LENS) consortium. LENS will be led by Argonne National Laboratory and includes five other DOE national laboratories such as Brookhaven, Lawrence Berkely and Sandia as well eight US universities.

“By leading the LENS consortium, Argonne will push sodium-ion battery technology forward and contribute to a secure energy future for everyone,” notes Argonne director Paul Kearns. ​“Our scientific expertise and dynamic collaborations in this important field will strengthen US competitiveness.”

The LENS consortium will now develop high-energy electrode materials and electrolytes for sodium-ion batteries as well as design, integrate and benchmark battery cells with the aim of creating high-energy, long-lasting batteries.

“The challenge ahead is improving sodium-ion energy density so that it first matches and then exceeds that of phosphate-based lithium-ion batteries while minimizing and eliminating the use of all critical elements,” says LENS consortium director Venkat Srinivasan.

• Venkat Srinivasan, William Mustain and Martin Freer appeared on a Physics World Live panel discussion about battery technology held on 21 November 2024, which you can watch online now

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Stained glass is the most “physical” of all art forms. If you’ve ever been inside Chartres Cathedral in France or York Minster in the UK, you’ll know how such glass can transform a building by turning sunlight into gloriously captivating multicoloured patterns. What you might not realize, however, is that centuries of scientific innovation have forged this form of art.

Byzantine glaziers started making leaded glass windows back in the 6th century CE before the technique spread widely across Europe. But our ability to stain glass only emerged in the 14th century when medieval alchemists found that coating glass with silver nitrate and firing it in a kiln gave the material a range of orange and yellow hues.

Later, a range of other techniques were developed to produce various decorative effects, with stained glass becoming both an art and a craft. Particularly important has been the use of hydrofluoric acid – a poisonous and highly corrosive liquid – to strip off the surface of glass, layer by layer, to alter its colour and thickness.

Known as hydrofluoric acid etching, the technique is widely used by modern architectural glass artists. Beautiful patterns can be created by altering the strength and temperature of the acid and varying the time for which the glass is exposed to it. Materials like wax, bitumen and lead foil can also be used as resists to leave parts of the glass untouched.

Like other “glass artists”, I am an experimentalist of sorts. We use an empirical knowledge of glass to make beautiful objects – and sometimes even make new discoveries

Like other “glass artists”, I am an experimentalist of sorts. We use an empirical knowledge of glass to make beautiful objects – and sometimes even make new discoveries. In fact, some historians say that hydrofluoric acid was first created in 1670 by a German glassworker named Heinrich Schwanhardt.

While treating a mineral called fluorspar with acid, he saw that the lenses in his spectacles went cloudy – prompting him to start using the same reaction to etch glass. Only much later – in the late 18th century – did chemists carry out “proper” lab experiments to show that flourspar (calcium fluoride) reacts with the acid to create what we now call hydrofluoric acid.

From the 19th century onwards, acid-etching techniques started to be used by numerous stained-glass artists and studios throughout Britain and Ireland. Dublin-born Harry Clarke (1889–1931) was the leading proponent of the hydrofluoric acid-etching technique, which he mastered in an exceptionally personal and imaginative manner.

Art of glass

I first came across acid etching in 2010 while studying glass and architecture at Central Saint Martins, which is part of the University of the Arts London. The technique intrigued me and I started wondering about its origins and how it works, from a scientific point of view. What chemical processes are involved? What happens if you vary how the acid is applied? And how can that create new decorative effects?

Unable to find full answers to my questions, I started carrying out my own experiments and investigations. I wanted to understand how fluorspar – which can be colourless, deep green or even purple – can be turned into hydrofluoric acid and what goes on at a chemical level when it etches glass.

During my investigations, which I published in 2014 in The Journal of Stained Glass (38 146), I was astonished to find references to glass in the famous lectures given by Richard Feynman about quantum electrodynamics. Published in book form as QED: the Strange Theory of Light and Matter, Feynman explained the partial reflection of light by experimenting with blocks of glass.

He showed that the amount of light reflected increases with the thickness of the glass, pointing out that photons interact with electrons throughout the material, not just on the surface. “A piece of glass,” Feynman wrote, “is a terrible monster of complexity – huge numbers of electrons are jiggling about.”

In my own work, I’ve recently been experimenting with glass of different thickness to make a piece of art inspired by the packaging for a quantum chip made by Rigetti Computing. Entitled Per scientiam ad astra (through science to the stars), the artwork was displayed at the 2024 British Glass Biennale at the Ruskin Glass Centre in Stourbridge, UK – a historically significant area for glass-making that pioneered the creation of etched glass in the 19th century.

A quantum rose

Creating an artwork based on quantum technology might be an unusual thing to do, but when I saw a photo of the packaging for a quantum chip back in 2020, I was astounded by the elegant geometry of this enigmatic object, which holds the “brain” of the company’s quantum computer (see box above). Reminding me of the beautiful circular rose windows of medieval cathedrals, I wanted to use glass to create a “quantum rose” for the 21st century. Later, Rigetti got in touch with me after my plans were reported on in Physics World in June 2022.

As you can imagine, hydrofluoric acid etching is an extremely dangerous technique, given how corrosive the liquid is. I acid-etch glass from the German company LambertsGlas in a specially equipped studio with a ventilation cabinet to extract fumes and I wear a protective suit with a respiratory mask. As you can see from the video below, I look more like an astronaut than an artist.

Acid etching can be done in lots of different ways (see Materials Today Proceedings 55 56) – but I prefer to apply the acid freely with a cotton or plastic brush, coining my technique “acid painting”. The resulting artwork, which took me several months to make, is just over a metre in diameter.

• This video has no voice over.     (Video courtesy: Space Production)

Mostly blue with a red focal point, the artwork constantly changes as you move around it. Visitors to the British Glass Biennale seemed to be attracted to it, with comments such as “empowering” and “ethereal”. Per scientiam ad astra will now move to a private residence that just happens to be not far from the UK’s National Quantum Computing Centre in Oxfordshire, where one of Rigetti’s quantum computers is housed.

Art–science crossover

Stained-glass windows were once “illuminated books” for people who could not read – mysterious transmitters of knowledge that told stories about human life. The same, in a way, is true of quantum computers, which are broadening our understanding of reality. And just as mathematical equations can have an inner beauty, so too do quantum computers through the myriad technological innovations that underpin them.

With 2025 being the International Year of Quantum Science and Technology, I hope my artwork raises interesting questions at the intersection between art and science, continuing the “two-cultures” dialogue introduced by C P Snow in 1959. Is it a metaphorical window into the secret architecture of the universe? Or is it a visualization of our reality, where Newtonian and quantum-mechanical worlds merge?

Working with stained glass requires an understanding of how materials behave but that knowledge will only get you so far. To reveal new regions of reality and its beauty, unexpectedness plays a role too. Stained-glass art is the convergence of certainty and uncertainty, where science and art come together. Art can unite people; and through the beauty in art, we can create a better reality.

The post A ‘quantum rose’ for the 21st century: Oksana Kondratyeva on her stained-glass art inspired by a quantum computer appeared first on Physics World.

Xenon nuclei change shape as they collide, transforming from soft, oval-shaped particles to rigid, spherical ones. This finding, which is based on simulations of experiments at CERN’s Large Hadron Collider (LHC), provides a first look at how the shapes of atomic nuclei respond to extreme conditions. While the technique is still at the theoretical stage, physicists at the Niels Bohr Institute (NBI) in Denmark and Peking University in China say that ultra-relativistic nuclear collisions at the LHC could allow for the first experimental observations of these so-called nuclear shape phase transitions.

The nucleus of an atom is made up of protons and neutrons, which are collectively known as nucleons. Like electrons, nucleons exist in different energy levels, or shells. To minimize the energy of the system, these shells take different shapes, with possibilities including pear, spherical, oval or peanut-shell-like formations. These shapes affect many properties of the atomic nucleus as well as nuclear processes such as the strong interactions between protons and neutrons. Being able to identify them is thus very useful for predicting how nuclei will behave.

Colliding pairs of ¹²⁹Xe atoms at the LHC

In the new work, a team led by You Zhou at the NBI and Huichao Song at Peking University studied xenon-129 (¹²⁹Xe). This isotope has 54 protons and 75 neutrons and is considered a relatively large atom, making its nuclear shape easier, in principle, to study than that of smaller atoms.

Usually, the nucleus of xenon-129 is oval-shaped (technically, it is a 𝛾-soft rotor). However, low-energy nuclear theory predicts that it can transition to a spherical, prolate or oblate shape under certain conditions. “We propose that to probe this change (called a shape phase transition), we could collide pairs of ¹²⁹Xe atoms at the LHC and use the information we obtain to extract the geometry and shape of the initial colliding nuclei,” Zhou explains. “Probing these initial conditions would then reveal the shape of the ¹²⁹Xe atoms after they had collided.”

A quark-gluon plasma

To test the viability of such experiments, the researchers simulated accelerating atoms to near relativistic speeds, equivalent to the energies involved in a typical particle-physics experiment at the LHC. At these energies, when nuclei collide with each other, their constituent protons and neutrons break down into smaller particles. These smaller particles are mainly quarks and gluons, and together they form a quark-gluon plasma, which is a liquid with virtually no viscosity.

Zhou, Song and colleagues modelled the properties of this “almost perfect” liquid using an advanced hydrodynamic model they developed called IBBE-VISHNU. According to these analyses, the Xe nuclei go from being soft and oval-shaped to rigid and spherical as they collide.

Studying shape transitions was not initially part of the researchers’ plan. The original aim of their work was to study conditions that prevailed in the first 10^-6 seconds after the Big Bang, when the very early universe is thought to have been filled with a quark-gluon plasma of the type produced at the LHC. But after they realized that their simulations could shed light on a different topic, they shifted course.

“Our new study was initiated to address the open question of how nuclear shape transitions manifest in high-energy collisions,” Zhou explains, “and we also wanted to provide experimental insights into existing theoretical nuclear structure predictions.”

One of the team’s greatest difficulties lay in developing the complex models required to account for nuclear deformation and probe the structure of xenon and its fluctuations, Zhou tells Physics World. “There was also a need for compelling new observables that allow for a direct probe of the shape of the colliding nuclei,” he says.

Applications in both high- and low-energy nuclear and structure physics

The work could advance our understanding of fundamental nuclear properties and the operation of the theory of quantum chromodynamics (QCD) under extreme conditions, Zhou adds. “The insights gleaned from this work could guide future nuclear collision experiments and influence our understanding of nuclear phase transitions, with applications extending to both high-energy nuclear physics and low-energy nuclear structure physics,” he says.

The NBI/Peking University researchers say that future experiments could validate the nuclear shape phase transitions they observed in their simulations. Expanding the study to other nuclei that could be collided at the LHC is also on the cards, says Zhou. “This could deepen our understanding of nuclear structure at ultra-short timescales of 10^-24 seconds.”

The research is published in Physical Review Letters.

The post Nuclear shape transitions visualized for the first time appeared first on Physics World.

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