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Water transforms into gold-coloured metallic solution

A metallic water solution has been observed in the laboratory for the first time thanks to a new method that bypasses the need for extremely high pressures. By reacting water with an alkali metal in a way that avoids the usual explosive outcome, an international team of researchers showed that they could produce a gold-coloured conducting layer on the surface of the resulting solution – a rare example of a modern scientific result visible to the naked eye.

In principle, any insulating material can be transformed into a metal by applying a high enough pressure to it. For pure water, the pressure required is 48 megabars – a value that is way beyond what is possible in laboratory experiments and may be literally astronomical, existing only inside the cores of large planets or stars.

At pressures obtainable in the laboratory, researchers recently showed that water could be made superionic, containing high-conductivity protons. A metallic state containing conductive electrons, however, was thought to be out of reach.

Suppressing explosions

Researchers led by Pavel Jungwirth have now turned this idea on its head by reacting water with a sodium-potassium (NaK) alloy to produce a metallic water solution. To do this, they first had to suppress the explosive reaction – a favourite of school science experiments – that normally occurs when water and an alkali metal come together.

“We know that dissolving alkali metals in water leads to explosions, so we did it the other way around,” Jungwirth says. “We blew a tiny amount of water at pressures as low as 10-4 mbar onto a NaK alloy drop squirted from a micronozzle at a dripping rate of about one drop every 10 s in vacuum.”

When there is no water vapour in the vacuum chamber, the NaK drops have a silver metallic sheen. This lack of visible colour occurs because alkali metals do not have d or f electrons that can be optically excited and produce colour via photoluminescence. When the researchers introduced water into the chamber, Jungwirth says they were “lucky enough” to find a water vapour pressure (~10-4 mbar) at which roughly 100-nm-thick layers of water begin to form on the alkali metal drop. At this pressure, the underlying alkali metal layer dissolves faster than the metal and water can react, forming a metallic water solution.

Surface layer turns golden

Once enough water adsorbs to the surface of the NaK drops, the researchers report that the surface layer turns gold almost immediately and remains in that condition for up to ~5 s. After this point, as water continues to adsorb, the drop’s colour changes to bronze for another 2−3 s. Eventually, the drop loses its metallic sheen, turning purple/blue and finally white as an alkali hydroxide layer forms as a product of the alkali metal-water reaction.

The whole process lasts for about 10 s, during which time the drop grows and reaches its final size of ~5 mm in diameter. It then falls off the end of the nozzle and a new drop starts to grow. This process can continue for a “train” of hundreds of drops, provided the water vapour pressure remains in a relatively narrow range around its optimal value. The trick, Jungwirth says, is to use only a tiny amount of water and go directly to the concentrated metallic regime. It also helps that the delocalized (metallic) electrons are less reactive than the localized solvated electrons.

Concentrated metallic regime

The researchers used optical and photoelectron spectroscopy techniques to characterize the metallic nature of the drop’s surface layer. They estimate that this layer contains around 5 × 1021 electrons per cubic centimetre. While the practical applications of creating a 100-nm-layer of metallic water that lasts for a few seconds are most likely zero, Jungwirth notes that the experiment is “really beautiful” and easy to follow. “My hope is that if a smart high school kid sees this, they may decide to study physics or chemistry,” he tells Physics World.

The researchers, who report their work in Nature, say they now plan to map in detail the metal-to-electrolyte transition upon diluting the metallic water layer with more water, as they did for metallic ammonia last year.

New non-COVID research projects plunge by a third since the start of the pandemic

The COVID-19 pandemic may be having subtle but long-lasting impacts on scientific activities – especially on women researchers and those with young children. That is according to a new US analysis, which suggests that the number of non-COVID research projects being initiated may have fallen by almost a third since the start of the pandemic. Researchers’ working hours are, however, now returning to pre-pandemic levels.

In their study, management scientist Dashun Wang of Northwestern University in Illinois and colleagues compared the results of two online surveys examining the impact of COVID-19 on the working lives of scientists in Europe and the US. The first survey was undertaken in April 2020 and had 4535 respondents, while the other was conducted in January of this year and received 6982 replies.

The disproportionate impact the pandemic has had on women and parents of young children means that there is a risk academia will permanently lose talented researchers

Tatyana Deryugina, University of Illinois at Urbana-Champaign

COVID-19 has dramatically affected research output. Respondents who were not involved in COVID-related studies said they had published 9% fewer papers and reported a 14.8% drop in submissions – consistent with measurements of publication rates. Meanwhile, 27% of respondents said they had launched no new projects at all in 2020, whereas only 8.9% has started none in the previous year.

These figures, the authors say, mean that the full impact of the pandemic has not yet emerged. In particular, respondents not involved in COVID research reported an average decrease in new projects of 36.2% in 2020, the equivalent of losing one new project (of the usual three) per scientist. This decline in new projects appears to be the same across all scientific disciplines, but it has disproportionately affected women and people with young children.

Disproportionate impact

Wang and colleagues speculate that the decrease in new non-COVID projects may stem from fewer of the face-to-face and spontaneous interactions that trigger ideas – a notion supported by a fall in new collaborations seen in pre-print authorships in late 2020. The psychological toll of the pandemic may be to blame too, the authors say.

There are some brighter spots too. Respondents to the first survey reported that their weekly working time had dropped by an average of 7.1 hours in comparison with pre-COVID levels, but by the time of the second survey in January, the difference was only 2.2 hours on average. The situation is also brighter for scientists directly involved in COVID-related research, for whom the pandemic appears to have had little impact on working hours, publications and project initiation.

“Understanding how COVID is changing scientific productivity is crucial not just for predicting how academic output will be affected by this pandemic in the long run, but also for designing policies that mitigate [its] effects,” says Tatyana Deryugina, an economist at the University of Illinois at Urbana-Champaign, who was not involved in the study but has examined the effects of the pandemic on women academics. “The disproportionate impact on women and parents of young children means that there is a risk academia will permanently lose talented researchers because of this temporary shock unless countervailing policies are implemented.”

Rebecca Krukowski – a behavioural scientist at the University of Tennessee who was also not involved in the study – says that the ongoing impacts COVID on childcare and schools is having a huge impact. “It makes sense that women and parents of small children do not have the bandwidth to brainstorm new projects or forge new collaborations,” she adds. “They are, not surprisingly, barely keeping their heads above water, without much support.

The study is described in a paper on arXiv.

Variable-stiffness catheter could increase the safety of robotic eye surgery

A surgical catheter that can change its rigidity as needed during operations has been developed by researchers from Switzerland and Spain. The tool – the core of which is built from a tailored phase-change alloy – could improve the safety of minimally-invasive ophthalmic surgeries.

One procedure that could benefit from such a tool is epiretinal membrane peeling, a delicate surgery that only highly skilled surgeons can perform. Epiretinal membranes are thin, transparent layers of fibrous tissues that can form over the retina and, in severe cases, cause one’s vision to become blurred and distorted. They most commonly arise in those aged 50 and older, as a result of age-related detachment of the vitreous jelly from the retina. However, the condition can also manifest following ocular surgery, inflammation of the eye or as a consequence of diabetic retinopathy. It is estimated that some 2% of people aged 50 or older – and 20% of 75-year-olds – have such membranes in one or both eyes, although treatment is usually only necessary in around 15% of cases.

Epiretinal membranes are removed in a surgical procedure that sees the pathological cell layer – which is typically some 60 µm thick – gently peeled off by a tiny, rigid gripping tool inserted into the eye. To reduce the risk of harming the sensitive retina, the operation starts with the vitreous being removed from the patient’s eye and replaced with a saline solution that is less susceptible to transferring potentially damaging shear forces. Nevertheless, the procedure still relies on the finely controlled application of force to avoid retinal tearing.

To minimize this risk further, medical roboticist Quentin Boehler of ETH Zurich and colleagues have developed a new type of catheter comprising a core made of a low melting point alloy (LMPA) that’s sandwiched, alongside a heating wire, between two insulating polymer layers. The device is just 1 mm thick in total.

Schematic views
(A) Cross-section of the variable-stiffness catheter. (B) Central heating causes the LMPA to melt from the inside out, shifting the phase boundary radially outward. (C) Overview and close-up of the proposed catheter. (Courtesy: CC BY 4.0/Adv. Science 10.1002/advs.202101290)

As its temperature rises, the alloy progressively melts from its core outwards, resulting in an increase in flexibility that can be reversed by allowing the catheter to cool back down. The alloy is tuned such that the phase transition occurs at 47°C – above the temperature of the human body (37°C), but not so high as to cause physiological damage.

A resistance-measuring wire contained in the catheter’s outer insulating layer allows operators to monitor the alloy temperature and, by extension, ensure the desired liquid-to-solid ratio and corresponding rigidity. In this way, the catheter – which has a magnetic tip – can be safely navigated, by an external magnetic field, to its desired target in its soft state before being allowed to stiffen in order to deliver the desired force to the pair of grippers at its end.

According to the team, the wire takes approximately 16 s to heat to a fully flexible state under surgical conditions and some 30 s to cool back down, and can deliver forces that range from 20 mN to 8 N. To demonstrate the potential of the concept, the researchers successfully performed a simulated membrane peeling operation on an eyeball phantom, onto which they had pressed a thin Parafilm layer to simulate the unwanted cell layer.

“We believe that our approach simply provides much more safety to the procedure,” says Boehler, noting that the catheter can also be adapted into a microcannula to inject drugs behind the retina. “More generally, we believe that variable-stiffness soft continuum robots can be part of the next generation of minimally invasive medical tools using robotic assistance, as they will benefit from increased safety and dexterity provided by this feature.”

“While shape morphing instruments have been available in laparoscopic surgery for a while, at the submillimetre level at which eye surgery is performed such capabilities were until now not possible,” comments Marc de Smet, an ophthalmic surgeon from the MIOS Centre in Lausanne who was not involved in the present study. However, he added, the current time constants are “relatively long in the hands of a surgeon poised to carry out a task that might involve 60 s in a given position”.

Furthermore, he continued, “while a 1 mm diameter is considerable achievement, current vitreoretinal surgery is carried out at diameters of 0.63 mm or less. At 1 mm, sutures are required at the end of surgery to close the wound, while at 0.63 mm or less, suture-less surgery associated with rapid healing is possible.”

With this initial study complete, the researchers are moving to demonstrate their catheter in animal models, with the goal of delivering a human intervention in the near future.

The study is described in Advanced Science.

Nanostructures make brighter e-reader displays

Thinking of taking your e-reader on holiday this summer? Sitting around in the sunshine catching up on all the books you haven’t had time to read may soon be even more enjoyable thanks to a new reflective screen technology that works without a backlight. Developed by Andreas Dahlin and colleagues at Sweden’s Chalmers University, the technology is based on colour-changing nanostructures, and it could be a promising alternative to the energy-intensive digital screens currently employed in smartphones and tablets.

Conventional digital screens require a backlight to illuminate the text or images they display. Not only does this require extra energy, it also means that screens are sometimes too dim to be comfortably used outdoors – especially on bright, sunny days.

To overcome this problem, researchers have been exploring ways of incorporating so-called structural colours into the “electronic paper” of reflective displays. Materials that exhibit structural colour do not contain dyes and pigments. Instead, they rely on nanostructures that reflect or scatter light waves of certain frequencies, and they do not fade over time – especially if the structures are made of less-reactive “noble” metals such as gold or platinum.

Not bright enough

One particularly promising technique for making structural colours is to combine metallic nanostructures with materials that are electrochromic – that is, they change colour when a small electrical voltage is applied to them. Until now, however, devices based on the strongly electrochromic material tungsten trioxide (WO3) often lacked colour purity (chromaticity) and were not bright enough for practical applications.

The Chalmers team explains that this lack of brightness (low reflectance) poses a serious challenge for designers of electronic paper because only a fraction of the display’s surface will show a given colour when using subpixels arranged side by side. To reduce the number of subpixels required, they needed to create electrochromic surfaces that can provide many different colours.

Inverted design

In their latest study, Dahlin and colleagues developed a new type of inorganic electrochromic nanostructure that has both a high reflectance and an excellent colour range. They did this by modifying the design of an ultrathin flexible material based on layers of WO3, gold and platinum that they previously developed in their laboratory. While this older design could reproduce all the colours an LED screen can display and required only a tenth of the energy of a standard tablet, the colours on this earlier reflective screen were not displayed with optimal quality.

The researchers have now reversed the thin-film layers within this structure in a way that allows all the electrical components to be “hidden” behind the reflective surface. This involved placing the electrically conductive material in the device underneath the pixelated nanostructure that reproduces the colours, rather than above it as was originally the case. “The new design means you look directly at the pixelated surface, therefore seeing the colours more clearly,” Dahlin explains. “They can be seen through a glass cover, which will make colour images much easier to see in a real device.”

Commercialization prospects

The researchers showed that their nanostructures clearly outperform the best colour e-reader on the market today in terms of both colour range/quality and brightness, and Dahlin is confident that a product containing the new technology could be developed commercially within a “couple of months if a large player on the market really decides to give it a try”.

“As well as smart phones and tablet screens, the main application would be colour-changing surfaces or displays for use in situations where light is high, such as outdoors during the day,” he tells Physics World. “The devices are not fast enough to show video, so if used in advertising, they would offer energy and resource savings compared with both printed posters or moving digital screens.”

The researchers, who report their work in Nano Letters, say they are now trying to make the same nanostructures using another process that wastes less gold and platinum in the preparation stage.

Summer internships: Constantine Pelesis – ‘I built up my network and got an understanding of how a whole company works together’

Before looking for an internship, Constantine Pelesis already knew that he wanted to go into nuclear medicine. “I was studying part-time for a Master’s degree in medical physics with the University of Surrey, while also working as a teaching assistant there.” In the first summer of his MSci course he was looking for something that would give him some experience, help him to broaden his network, and provide some extra income. He therefore contacted the South East Physics Network (SEPnet), an organization that works across nine universities in south-east England to support physics students in finding placements.

Although SEPnet didn’t have any vacancies, it put Pelesis in touch with Adaptix, a company in Oxfordshire working on medical-physics devices, and he sent an e-mail to express his interest. Adaptix later called him when an internship position came up that was relevant for him, showing that it’s always worth expressing your interest. Even if there are no internships available at the time, situations can change and new opportunities are always emerging.

“Adaptix sent me a job description with the different projects it had available, and I applied with a cover letter and a CV,” Pelesis recalls. “I was invited to an interview with the chief science officer, who then became my supervisor when I was offered the internship.” After learning he had been successful, he moved to Oxford for the summer. “I loved getting to know Oxford and I did a lot of exploring while I was there,” he says. “I visited many places where they filmed Harry Potter, and I also explored the countryside around the city. Adaptix is just outside the city and my commute was a walk along the river every day.”

During the internship, Pelesis worked on computational modelling of X-rays. “I learnt how to use a new software package to do Monte Carlo simulations of electrons interacting with a metal plate,” he says. “ These simulations predicted how much energy would be deposited when the electrons generated X-rays, and how this varied depending on the set-up of the equipment. It isn’t as good as doing a physical experiment, but it gives you some initial signs about which set-ups look most promising, so that fewer need to be tested experimentally.”

Pelesis emphasizes the importance of the soft skills he developed while he was there, through working as part of a team and giving presentations on his project. He recommends speaking to lots of people across a company to get a broader view and make the most out of an internship. “I talked to people from different departments about their roles and got an understanding of how a whole company works together. It’s also good for building up your professional network.”

I talked to people from different departments about their roles and got an understanding of how a whole company works together. It’s also good for building up your professional network.

Constantine Pelesis

After his internship, Pelesis stuck with his plan to go into medical physics, and now works for the National Health Service as a nuclear medicine clinical technologist at Singleton Hospital in Swansea. This involves carrying out various procedures, such as administering radiopharmaceuticals to patients and using gamma ray cameras to image their internal organs, to see if they are functioning properly. As a next step in his career, he wants to become a clinical scientist, which would involve more work on quality control of the medical machines and radiation protection, and less patient-facing work.

Pelesis advises prospective interns to not only ask their university departments about opportunities, but also search widely online and get a LinkedIn account. “It’s another way of finding opportunities and seeing what jobs are out there,” he says. “It also enables you to make the most out of your internship by keeping in touch with the people you meet there.” Pelesis is still in contact with his Adaptix supervisor, who has introduced him to other people who work with the NHS in Wales. “An internship is a great opportunity to learn from people and build up your network,” he says. “You never know where it might lead.”

Estimating patient size from X-ray data improves radiation risk assessment

Size estimates
The X-ray attenuation of the patient calculated from the DICOM header information of chest X-rays, and compared with CT gold-standard size measures. (Courtesy: Hilde Bosmans)

More than 3.6 billion diagnostic imaging exams are performed each year across the globe, with medical radiation use accounting for 98% of the population’s dose from artificial sources. To keep track of this radiation burden, radiology departments employ dose management systems that extract information from X-ray exams to estimate patients’ radiation levels or flag suspicious dose outliers.

The size of a patient will influence their individual organ doses. But for projection radiography (two-dimensional X-ray imaging), dose management systems don’t usually have access to such information. Instead, they use conversion factors based on a reference patient, resulting in less accurate dose calculations.

To address this shortfall, researchers in Belgium have developed a metric to estimate patient size directly from the X-ray images. Importantly, the new metric only uses parameters available in the header of the patient’s DICOM files (which store medical images and related data). They describe the approach in Physics in Medicine & Biology.

“Having a structured, validated methodology for size estimation using DICOM header information paves the way for automated size-specific dosimetry in digital radiography,” explains Hilde Bosmans from the University Hospitals Leuven. “With the widespread adoption of dose management systems that track the patient’s dosimetric records, patent-specific effective organ dose calculations will allow for better data in terms of radiation-induced risks. This is valuable for all patients, and particularly for obese or thinner patients and patients that undergo X-ray exams regularly.”

Metric definition

Bosmans and colleagues proposed an attenuation metric related to the dose absorbed in the patient – based on the ratio of incident air kerma to detector air kerma – that correlates with patient size. They defined this metric for both thoracic and abdominal projection radiography, using 137 thoracic and 137 abdominal projection images as input data. These patients also had recent CT exams of the same body part, serving as the gold standard for patient size.

Attenuation metric
The researchers hypothesized that an attenuation metric, related to the ratio of detector air-kerma to incident air-kerma (DAK/IAK), would inversely relate to the patient size. (Courtesy: Phys. Med. Biol. 10.1088/1361-6560/ac0d8c)

To establish the ground-truth patient size, the researchers used the CT scans to calculate the water equivalent diameter (WED) and water equivalent thickness (WET) of all patients. They then plotted these ground-truth WED and WET values versus the natural log of the attenuation metric, for both thoracic and abdominal scans. This generated four correlation curves that could then be applied to estimate patient size based solely on DICOM information from the projection radiographs.

The team note that some of the DICOM fields required for this approach (exposure index, kerma–area product, exposed area and source–detector distance) are optional. “They are, however, usually available in the DICOM header or could be made available by the system vendor,” says Bosmans. “In several countries, it is even mandatory to have these data displayed. After all, they are important indices to monitor the practice and the equipment, and they can unravel problems or occasional malpractice.”

The researchers validated the technique’s ability to estimate patient size using four different radiography systems. For all devices, they examined X-ray exams from 50 new patients and used the correlation curves to estimate WED and WET values based on the DICOM information.

Three of the systems (Carestream’s DRX Evolution, Siemens’ Axiom Luminos dRF and Canon’s CXDI-11) included a standardized exposure index, in which the exposure index is linearly proportional to the detector air kerma (rather than being vendor-specific), thereby enabling consistent performance evaluation across devices and departments.

For thoracic exams on these systems, the differences between estimated and ground-truth WED were all within ±15%, with absolute differences of 4% on average. Estimated WET values had absolute differences of 8%, 7% and 7%, for DRX Evolution, Axiom Luminos dRF and CXDI-11, respectively. In the two systems used to perform abdominal scans, the average absolute differences between estimated and ground-truth values were 4% and 6% for WED, and 6% and 8% for WET.

The researchers also examined a system without standardized exposure index: the Triathlon DR from Oldelft. For thoracic exams, the technique underestimated WED and WET, with average differences from the ground truth of –36% and –57%, respectively. For abdominal scans, the algorithm gave similar results to the other systems, with deviations of 3% for WED and 5% for WET.

Improved accuracy

The researchers suggest that the new metric could enable individualized risk assessments with better accuracy than using a generic conversion factor. They emphasize that their method is in principle applicable to all devices that acquire X-ray projections. Including patient size in a dose management platform would improve the dosimetric data and improve dose outlier management by reducing false positives from overweight patients and false negatives due to underweight patients.

Bosmans notes that this development is part of a larger project to create, along with personalized CT dose estimates, automated personalized dosimetry for 2D projection imaging. The research is performed in collaboration with the medical software company Qaelum and supported by a Flemish VLAIO grant. The intention is to implement the automated size estimation metric into Qaelum’s dose and quality monitoring software.

“Ultimately, hospitals and patients will benefit from a total solution that will automatically evaluate the quality of the exam at the one side and provide advanced effective and organ dose estimations in X-ray imaging at the other,” she tells Physics World.

X-ray flares spotted from behind a black hole

X-ray flares originating from behind a black hole have been observed for the first time – by an international team led by Dan Wilkins at Stanford University in the US. The wavelength-shifted X-ray flashes are believed to have originated as photons that collided with the black hole’s inner accretion disc, before being redirected towards Earth by the black hole’s colossal gravity. By observing the effect in more detail, astronomers could gain important insights into the immediate surroundings of black holes.

Just before material passes across the inescapable event horizon of a black hole, theories predict that it is superheated to millions of degrees, forming a rotating corona of plasma surrounding the black hole. Meanwhile, the black hole’s magnetic field is continually twisting, snapping and recombining as the plasma rotates. This magnetic activity imparts colossal amounts of energy on plasma electrons, which produces intense, characteristic flashes of X-rays.

While these events have been widely observed, recent calculations by Wilkins suggest that we should also see smaller, delayed X-ray flashes. These X-rays are emitted behind the black hole from our perspective – but then reverberate off the inner surface of its orbiting accretion disc. Due to Einstein’s general theory of relativity, these echoes should be bent around the black hole, and magnified by its intense gravitational field.

Dimmer flashes

Furthermore, the orbital motion of the accretion disc means that X-ray photon wavelengths will be shifted to varying degrees, depending on where within the disc they reverberate from. As a result, these dimmer flashes can offer glimpses of an environment completely obscured from our view.

In their study, Wilkins’ team made X-ray observations of the supermassive black hole at the centre of the I Zwicky 1 –  a galaxy about 59 million light-years away – using NASA’s NuSTAR telescope, and the ESA’s XMM-Newton instrument. Just as Wilkins predicted, both telescopes clearly detected energy-shifted X-ray flashes which followed brighter larger flares – providing key evidence that X-rays from behind the black hole had echoed off its accretion disc.

Through future observations of the effect, Wilkins and colleagues hope that astronomers could learn much more about the physical processes taking place in black hole coronas – which have so far proven notoriously difficult to study. The ideal opportunity for these measurements will come with the ESA’s Athena X-ray observatory, planned for launch in 2031. Featuring a far larger mirror than existing X-ray telescopes, the instrument will for the first time enable in-depth observations of X-rays originating throughout the entire coronas of black holes.

The research is described in Nature.

What do holidays mean to physicists in the 21st century?

I once went to a New Year’s Eve party when I heard a graduate physics student apologize for leaving early. He was working on an accelerator experiment, he explained, and his shift was starting at midnight. To the astonishment of almost everyone, he seemed to be looking forward to getting back into the lab. I, though, was not surprised, having interviewed enough scientists to recognize their enthusiasm for regarding leisure time as a precious opportunity to work.

The history of science is full of discoveries by researchers supposedly on holiday. Harold Urey, a chemistry professor at Columbia University, famously discovered deuterium on Thanksgiving Day 1931, which is a time when Americans cook, eat turkey and pumpkin, and hang out with relatives, including many they haven’t seen in a while. Not Urey, who sent the Physical Review a paper about his Thanksgiving Day work the following week, and won the Nobel Prize for Chemistry three years later.

In 1956 another Columbia researcher, Chien-Shiung Wu, and her husband were planning a vacation in the Far East to celebrate the 20th anniversary of their emigration from China. They had booked tickets on the Queen Elizabeth – but Wu backed out, and left her husband to take the trip alone. She wanted to take advantage of an opportunity that had arisen to investigate Tsung-Dao Lee and Chen-Ning Yang’s recent idea that parity conservation had not been experimentally tested in the weak interaction. By the beginning of the next year, Wu and her team discovered that parity was violated in the weak interaction, in one of the most surprising finds in the history of physics.

Another famous working-holiday find took place at the end of 1925, when the Austrian physicist Erwin Schrödinger, who was then married, went on a skiing vacation in Arosa, Switzerland with a girlfriend. He returned on 9 January 1926 with the rudiments of the wave equation that would revolutionize quantum physics, and earn him a share of the 1933 Nobel Prize for Physics (with Paul Dirac).

Moonlighting

I have also heard of physicists who have been caught secretly working while supposedly doing something else. The Israeli theoretical physicist Yuval Ne’eman, for example, was an active member of the Knesset in the 1980s, after helping to found a right-wing political party. However, he was often chastised by reporters and politicians after TV cameras swooped in on him during boring speeches and caught him doing physics equations.

In fact, I have often encountered the feeling that physicists view it as their right to work on holiday. I remember once asking a physicist about an interview he’d had for a job at Bell Labs. He told me that it had all gone well – until he’d asked if he’d be able to work in his lab over Thanksgiving. The interviewer hesitated, then finally promised him that he could. “And what about Christmas?” The interviewer hemmed and hawed, but could not commit. “I took the job anyway,” the physicist told me, frowning.

And even if you instruct physicists to take a break, they often don’t. During the summers in the early years of Brookhaven National Laboratory, scientists were expected to stop work early on Friday afternoons and go to a nearby beach on the south shore of Long Island. But I have it on good authority that on many such occasions some of them – including Lee and Yang, who were visiting the lab that summer – used sticks to write equations in the sand.

I recall speaking with one old-timer, whose name I have forgotten, who reminisced about the days when physicists travelled back and forth between the US and Europe by boat. They would typically have a blackboard installed in their staterooms – the old slate kind that you wrote on with chalk – and would use the journey of a week or so to let their imaginations fly. “I don’t know how today’s jet-setting physicists can do any serious thinking,” this person told me.

However, physicists do know how to relax. Albert Einstein liked sailing and the violin. Niels Bohr played football. And Robert Oppenheimer took postdocs to his New Mexico ranch, where he forbade them to talk of physics except when they had an eminent visitor. In one story, Oppenheimer took his guests horseback riding at midnight on a mountain ridge in a cold downpour in the middle of a lightning storm. Coming to a fork in the path, Oppenheimer said “That way it’s seven miles home, but this way it’s only a little longer, and it’s much more beautiful!”

But the passion with which physicists pursue these hobbies can have a dark side. The CERN experimental physicist Paul Musset, who was a musician and climber in his spare time, died in a mountaineering accident on Mont Blanc in 1985. Musset was 52, an active researcher who sometimes worked nearly through the night, and had been a candidate for the Nobel prize as a co-discoverer of weak neutral currents. I also recall one male experimental physicist confessing to me how ashamed and guilty he felt staying in the lab to do an experiment early in his career. Expecting imminent crucial results, he ended up missing the birth of his first child.

The critical point

But perhaps what I have described is a thing of the past, and physics in the 21st century has become so professionalized and bureaucratic that today’s practitioners more frequently view it as a drudge that they can’t wait to break free of. Or maybe, with e-mail and Zoom calls constantly connecting us with the world, holidays don’t even give physicists a break. So do you view holidays as opportunities to interrupt your work, or to intensify it? Send me your experiences and I’ll write about them in a future column.

Radioactive marker enables imaging of iron-hungry cancer cells

There are many possible therapeutic options for treating patients with cancer. It would be incredibly helpful to be able to predict in advance which of these treatments might be successful. Thanks to research published in the Journal of Nuclear Medicine, we now have a new method to help determine whether a particular tumour might be successfully treated with iron-targeting cancer treatments.

An energetic solution

For cancer cells to endlessly multiply, they need a huge amount of energy. The machinery needed to generate that energy requires a lot of iron as a key building block. We have known for many years that cancer cells are hungry for iron. This has led to therapies being developed that target the significant iron reserves in tumour cells and turn this iron into a weapon to use against the cancerous cells.

Researchers at the University of California, San Francisco, have developed a way to assess the amount of available iron inside a cancer cell and therefore predict whether these new iron-targeting treatments might be effective on a particular patient’s tumour. This parameter has previously been impossible to measure.

“Iron rapidly oxidizes once its cellular environment is disrupted, so the intracellular form can’t be quantified reliably from tumour biopsies,” explains co-senior author Adam Renslo.

Instead, the researchers have developed a radiolabelled molecule that reacts with the available iron in cells and results in it getting stuck in those cells. The amount of this radiotracer retained in a cell is proportional to the amount of iron that was available in the cells initially. The radiolabel is already used widely in PET scans: a safe, detectable, radioactive fluorine-18 atom incorporated into the molecule’s structure. When the radioactive fluorine decays, it emits a positron, which can be detected outside the body using a PET scanner.

While testing this new method, the researchers found that the uptake of their labelled molecule correlated with the amount of an enzyme that processes the iron in the cell – indicating the likelihood of there being more iron present.

They also found that the success of treating different cancer cell types with iron-targeting drugs could be predicted by the uptake of their labelled molecule. PET images of the brain of a mouse with an implanted tumour clearly revealed the tumour amid the surrounding tissue.

Co-senior author Michael Evans notes that iron dysregulation “occurs in many human disorders, including neurodegenerative and cardiovascular diseases, and inflammation”. He says that being able to use this new tool in patients, to determine how much of this free iron is present and whether treatments targeting it may be successful, represents “an important milestone towards understanding the therapeutic potential” of these treatments.

Ultrathin glass films exhibit exotic liquid phase

Researchers in the US have discovered an entirely new liquid phase that arises as ultrathin films of glass are deposited directly onto cooled substrates. Led by Zahra Fakhraai at the University of Pennsylvania, the researchers used an intense X-ray source to reveal extremely dense, highly stable structures within the films, which transitioned to more conventional bulk liquids above a certain temperature.

Glasses typically form as a material undergoes rapid cooling from its molten state. Below a certain transition temperature, molecules within this supercooled liquid (SCL) slow down, allowing the material’s structure to solidify. The result is a substance with similar properties to a crystalline solid, but with atoms in a disordered configuration that more closely resembles a liquid.

If the glass is subjected to temperatures higher than its transition temperature, thermodynamic effects can drive its molecular structure into a state of equilibrium over time as the material gradually relaxes into structures such as droplets and ordered crystals. Although this effect is limited in bulk glass, it presents more of a problem for ultrathin, nanoscale glass films formed from SCLs. Due to their low transition temperatures, these useful materials are prone to forming droplets and crystals as they age, inhibiting the capabilities of small-scale features.

Keeping molecules mobile

To circumvent this issue, Fakhraai’s team used a technique called physical vapour deposition (PVD). Here, solid films form directly from gases as molecules are deposited onto a substrate. By keeping the substrate just below the transition temperature of the glass, the team ensured that the molecules remained mobile enough to rearrange themselves, and thus to adopt more stable configurations as they relaxed to their equilibrium state.

The result was a highly stable glass film with a structure that could not have been achieved through conventional techniques except via millions of years of ageing. To study the structure of this film in more detail, Fakhraai and colleagues used extremely powerful X-rays produced by the National Synchrotron Light Source II at Brookhaven National Laboratory.

Through this analysis, the team discovered that the PVD method produced an entirely new type of liquid. Arising within films between 25 and 55 nanometres thick, this liquid undergoes a phase transition to a typical bulk liquid at transition temperatures roughly 35 K cooler than ordinary SCL transitions. Intriguingly, this exotic new phase is extremely dense, with molecules more closely packed together than the researchers had thought was possible without applying immense pressures.

In future experiments, Fakhraai’s team hopes to study the parameters of this unique phase transition in more detail. The discoveries made could provide a deeper understanding of the behaviour of glasses as a whole. Subsequently, improvements to existing theories could serve as a predictive platform for developing new, more advanced glass-based materials.

The research is published in PNAS.

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