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Chernobyl’s hidden legacy

In June 1980 a doctor with the Oak Ridge Associated Universities in the US wrote a letter to a colleague at the Knolls Atomic Power Laboratory in upstate New York. The pair were corresponding about a forthcoming study of employee health at the Knolls reactor, and the doctor, C C Lushbaugh, wrote that he expected “little ‘useful’ knowledge” from this study “because radiation doses have been so low”. Even so, he agreed that the study had to be done because “both the workers and their management need to be assured that a career involving exposures to low levels of nuclear radiation is not hazardous to one’s health”. The results of such a study, he surmised, would help to counter anti-nuclear propaganda and resolve workers’ claims. However, they could also be a liability. If a competing union or regulatory agency got hold of the employees’ health data, Lushbaugh fretted, it could be weaponized. “I believe,” he continued, “that a study designed to show the transgressions of management will usually succeed.”

Lushbaugh’s dilemma is characteristic of research on the human health effects of exposure to low doses of radiation. He assumed he knew the results – good or bad – before the study began, because those results depended on how the study was designed. The field was so politicized, in other words, that scientists were using health studies as polemical tools and, consequently, asking few open-ended scientific questions.

A few years after Lushbaugh posted this letter, reactor number four at the Chernobyl nuclear power plant blew up, killing 31 workers and firefighters and spreading radioactive material across a broad area of what was then the Soviet Union (now Ukraine and Belarus) and beyond. The accident also exploded the field of radiation medicine and, for a while, promised to rejuvenate it. In August 1986, months after the accident, the chief of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), Giovanni Silini, advocated an enduring epidemiological investigation similar to research on atomic-bomb survivors in Japan [1]. Many other scientists concurred, hoping that Chernobyl could clear up ongoing controversies and uncertainties surrounding low-dose exposures.

**Lasting consequences** A scientist monitors radiation levels in a forest that was contaminated by the Chernobyl nuclear disaster and later burned in a forest fire. (Courtesy: Patrick Landmann/Science Photo Library)

It never happened. No long-term epidemiological study took place. That’s not to say there isn’t any information. A few summers ago I went to the Ukrainian national archives in the dusty, bustling outskirts of Kiev and asked the archivists for files on Chernobyl from Soviet Ukraine’s Ministry of Health. They laughed, telling me Chernobyl was a banned topic in the Soviet Union. “You won’t find anything,” they said.

They were wrong. I found dozens of collections labelled “The medical effects of the Chernobyl disaster”. I started reading and have not yet been able to stop.

The aftermath

In the years between 1986 and 1991, doctors and sanitation officials wrote to the Ministry of Health in Kiev with alarming accounts of widespread, chronic illness among the hundreds of thousands of children and adults living in contaminated territories. They recorded increases in tonsillitis, upper respiratory disease and disorders of the digestive tract and immune system. Between 1985 and 1988, cases of anaemia doubled. Physicians from almost every region in the zone of contamination reported a leap in the number of reproductive problems, including miscarriages, stillbirths and birth malformations. Nervous-system disorders surged. So did diseases of the circulatory system. In 1988, in the heavily contaminated Polesie region of northern Ukraine, 80% of children examined had upper respiratory diseases and 28% had endocrine problems. In Ivankiv, where many cleanup workers lived, 92% of all children examined had a chronic illness.

I also went to Minsk to check the archives in Belarus. There, I read reports that sounded eerily similar to the Ukrainian documents. These reports were classified “for office use only”, meaning that at the time, scientists were not free to exchange this information across districts or republics of the Soviet Union. Even so, independently, they were reporting similar, bad news. The problem grew so dire in Belarus that in 1990 officials declared the entire republic, which received more than 60% of Chernobyl fallout, a “zone of national ecological disaster”.

The Ukrainian and Belarusian reports, hundreds of them, read like a dirge from a post-catastrophic world. Doctors wrote from clinics in Kharkiv, far outside the contaminated zone, and described similar health problems among evacuees who had settled there. Physicians sent telegrams from Donetsk, where they were treating a complex of illnesses among young miners who had burrowed under the smouldering reactor in the days after the accident. Medical workers sent in to examine people in contaminated regions also fell ill.

In response, the Union of Soviet Radiologists penned a petition to alert Soviet leaders of the ongoing public health disaster. The president of the Belarusian Academy of Science sent a detailed summary of scientists’ findings to Minsk and Moscow. Even a KGB general, Mikhailo Zakharash, sounded the alarm. Zakharash, who was also a medical doctor, conducted a study of 2000 cleanup workers and their family members in a specially equipped KGB clinic in Kiev. In 1990, summing up four years of medical investigation, he wrote, “We have shown that long term, internal exposures of low doses of radiation to a practically healthy individual leads to a decline of his immune system and to a whole series of pathological illnesses.”

Chronic radiation

These findings track with what Soviet doctors had long described as chronic radiation syndrome, a complex of symptoms derived from chronic exposure to low doses of radiation. Researchers working on Chernobyl discerned a pattern of disease that tracked with pathways of radioactive isotopes entering the body, paths that began in either the mouth and headed towards the gastrointestinal tract or started in the lungs and followed blood into circulatory systems. Radioactive iodine sped to thyroids, they hypothesized, causing endocrinal and hormonal damage.

Critics, mostly in Moscow and the ministries of health, acknowledged the growth in health problems, but denied a connection to Chernobyl. A E Romanenko, the Ukrainian Minister of Health, is credited with inventing the word “radiophobia” to describe a public fear of radiation that induced stress-related illness. He and his colleagues also pointed to a screening effect from mass medical monitoring. Local doctors, they said, were projecting the diagnoses of chronic radiation syndrome onto their patients, blaming it for any illness found after Chernobyl.

There are some problems with these arguments. From 1986 to 1989, Chernobyl was a censored topic in the Soviet Union. Doctors could not exchange information about health problems, nor did they have access to maps of radioactive contamination. They only learned to be “radiophobic” by judging the bodies they examined. In the same years, doctors were also fleeing contaminated areas en masse, leaving hospitals and clinics in those regions staffed at 60%. As physicians left, so too did the chance for diagnosis, meaning that under-reporting of illnesses was more likely than a screening effect. Moreover, doctors from the northern regions of the Rivne province, which were at first judged clean and only in late 1989 designated contaminated, reported the same growth of illness as areas originally deemed “control zones,” regions with counts of more than 5 curies per square kilometre. The president of the Belarusian Academy of Science, V P Platonov, pointed to a vacuum of knowledge: “Until this time, no population has ever lived with continual internal and external exposures of this size.” Risk assessments assuring safe levels in the contaminated zones were extrapolated from the Japanese Atomic Bomb Survivor Lifespan Study, but these began only in 1950, five years after exposure. “Much is uncertain,” Platonov continued, “about fundamental aspects of the effects of low doses of radiation on human organs,” [2].

What happened to the 1980s Chernobyl health studies, which might have led to a renaissance in the field of radioecology? Essentially, they were overlooked. To figure out why, I went to the headquarters of the World Health Organization (WHO) in Geneva, to the UN’s archives in New York and the archives of UNSCEAR in Vienna. There, I found evidence of a conflict between branches of the WHO and the International Atomic Energy Agency (IAEA) over which organization would control the studies of Chernobyl health effects.

The risks and rewards of radiation

Colour-enhanced transmission electron micrograph showing radiation damage to chromosomes. The chromosomes appear as dark blobs with tendrils and bits and pieces of material scattered around the field of view

By 1989 angry crowds were questioning the Soviet Union’s handling of Chernobyl, and Soviet leaders asked foreign experts for help in assessing the disaster’s health impacts. The IAEA agreed, and Fred Mettler, a radiologist and American delegate to UNSCEAR, was appointed to head the medical section of an IAEA team. In 1990, as he and his team examined 1726 people in six contaminated zones and six control zones, Soviet doctors gave him 20 slides from children diagnosed with thyroid cancer. Thyroid cancer is very rare in children: before the Chernobyl accident, doctors saw eight or nine cases per year in all of Ukraine. Twenty cases in just three provinces was hard to believe. Dubious, Mettler brought the slides to the US to have them verified. They indeed indicated thyroid cancer.

Cancer cluster

Mettler mentioned this major medical finding in the 1991 International Chernobyl Project (ICP) technical report, but strangely, he also stated that there was “no clear pathologically documented evidence of an increase in thyroid cancer” [3]. The report concluded that there were no detectable Chernobyl health effects and only a probable chance of childhood thyroid cancers in the future. In a 1992 publication on thyroid nodules in the Chernobyl territories, Mettler failed to mention the 20 verified cases at all [4].

**Contamination** Many regions of modern-day Belarus, Ukraine and Russia experienced significant fallout after the Chernobyl meltdown. This map displays the levels of radiation from caesium-137 deposited on the ground. (Courtesy: UNSCEAR)

How could such a lapse occur? I found a confidential 1990 UN memo that seems relevant, particularly in light of the study-design problem set out in Lushbaugh’s letter a decade earlier. The memo suggests that the IAEA was conducting the ICP study to “allay the fears of the public” in service of “its own institutional interest for the promotion of peaceful uses of nuclear energy” [5]. The experiences of Keith Baverstock, then head of the radiation protection programme in the WHO’s European office, likewise reveal an institutional aversion to bad news. In July 1992 Baverstock planned to go to Minsk to examine childhood thyroid cases in Belarus, where doctors reported an astounding 102 new cases. At the last minute, officials from the WHO and the Commission of European Communities inexplicably pulled out of the mission. In an interview with me, Baverstock, an expert on the effects of ionizing radiation, said that a WHO official told him he could get fired if he went to Minsk.

He went anyway. With Belarusian scientists, he published news of the thyroid cancer epidemic in Nature. A top IAEA official complained angrily to the WHO, and the two agencies put pressure on Baverstock to retract his article. He refused, and a barrage of letters followed in Nature disputing the connection between the cancers and Chernobyl exposures [6]. Leading scientists from the US Department of Energy, the National Cancer Institute, Japan’s Radiation Effects Research Foundation and the IAEA argued that cancers were found because of increased surveillance. They called for a suspension of judgment and for further study. Repetitive and dismissive, their letters read like an orchestrated pile-on.

We now know that these global leaders in radiology were wrong. The numbers of cases rose into the thousands, too high to dismiss, and in 1996 the WHO and the IAEA finally admitted that skyrocketing rates of childhood thyroid cancer were most likely due to Chernobyl exposures. Today, the UNSCEAR maintains that the health consequences of the Chernobyl accident are limited to 31 direct fatalities – plus 6000 cases of children’s thyroid cancer [7].

Lingering questions

The question is – so what? Despite the 1991 ICP report’s erroneous claim of no health effects, UN agencies eventually recognized the cancer epidemic. What difference did a few years make? A great deal, it turns out. The ICP report also recommended that resettlements from the most contaminated regions should cease [8]. Consequently, the planned resettlement of 200,000 people living in areas contaminated with high levels of radiation (between 15 and 40 curies per square kilometre) slowed tremendously. The UN General Assembly had also been waiting for the report before raising funds for Chernobyl relief. The $646m budget (equivalent to about $1.1bn today) included medical aid, resettlement funds and a large-scale epidemiological study of Chernobyl health effects. The assertion by important UN agencies that there were no detectable health effects deflated that effort. Before the report, Japan had given $20m to the WHO, but afterwards it gave no more and complained about the funds being wasted. A few other countries gave sums totalling less than $1m, while the US and the European Community begged off entirely, citing the ICP report as a “factor in their reluctance to pledge” [9].

In subsequent years, IAEA and UNSCEAR officials cited the ICP report when discouraging Chernobyl-related health projects. In 1993 UNSCEAR scientific secretary Burton Bennett recommended that UN agencies suspend all programmes aimed at Chernobyl relief because they were unnecessary. He and IAEA administrator Abel Gonzalez, who led the ICP assessment, widely shared their views among UN agencies about “misinformation surrounding the Chernobyl accident” [10]. When the WHO, nonetheless, started a pilot study on Chernobyl health effects, Gonzalez wrote that he could not imagine what the WHO “expects to be able to detect for the level of doses in question”. Irked that WHO officials would examine any effects but psychological ones, he charged, “The World Health Organization seems to ignore, expressly or tacitly, the conclusions and recommendations of the International Chernobyl Project,” [11].

The consequences of this moment of deviant science continue 30 years later. Today we know little about the non-cancerous effects that Soviet scientists working in contaminated zones reported in the late 1980s, and which they attributed to internal and external exposures to ionizing radiation. Are these effects as real as the childhood thyroid cancers proved to be? The Soviet post-Chernobyl medical records suggest that it is time to ask a new set of questions about long-term, low-dose exposures.

References

Giovanni Silini 1986 “Concerning proposed draft for long-term Chernobyl studies” Correspondence Files, UNSCEAR Archive
V P Platonov and E F Konoplia 1989 “Informatsiia ob osnovynkh rezul’tatakh nauchnykh rabot, sviazannykh s likvidatsiei posledstvii avarii na ChAES” RGAE 4372/67/9743: 490
International Chernobyl Project, Proceedings of an International Conference (Vienna: IAEA 1991): 47. Mettler also admitted that the slides checked out at the Vienna conference convened to discuss the report. For a discussion of thyroid cancer, see The International Chernobyl Project, Technical Report, Assessment of Radiological Consequences and Evaluation of Protective Measures (Vienna: IAEA 1991): 388
Fred Mettler et al. 1992 “Thyroid nodules in population around Chernobyl” Journal of American Medical Association 268 616
From Enrique ter Horst, Asst Sec Gen, ODG/DIEC to Virendra Daya, Chef de Cabinet, EOSG, 16 April 1990, United Nations Archive, New York S-1046 box 14, file 4, acc. 2001/0001
Baverstock et al. 1992 “Thyroid cancer after Chernobyl” Nature 359 21; Kazakov et al. 1992 “Thyroid cancer after Chernobyl” Nature 359 21; I Shigematsu and J W Thiessen 1992 “Childhood thyroid cancer in Belarus” Nature 359 680; V Beral and G Reeves 1992 “Childhood thyroid cancer in Belarus” Nature 359 680; E Ron, J Lubin, A B Scheider 1992 “Thyroid cancer incidence” Nature 360 113
“The Chernobyl accident: UNSCEAR’s assessments of the radiation effects” UNSCEAR website
The International Chernobyl Project: an Overview (Vienna: IAEA 1991): 44
“International co-operation in the elimination of the consequences of the Chernobyl Nuclear Power Plant accident” 24 May 1990, UNA S-1046/14/4; “Third meeting of the Inter-Agency Task Force on Chernobyl” 19–23 September 1991, WHO E16-445-11, 5; “Briefing note on the activities relating to Chernobyl” 3 June 1993, Department of Humanitarian Affairs DHA, UNA s-1082/35/6/, acc 2002/0207; Anstee to Napalkov, 17 Jan 1992, WHO E16-445-11, 7
Gonzalez to Napalkov, 10 August 1993, WHO E16-445-11, 19; B G Bennett 1993 “Background information for UNEP representative to the meeting of the Ministerial Committee for Coordination on Chernobyl” 17 November 1993, New York, Correspondence Files, UNSCEAR Archive, Vienna
Gonzalez to Napalkov, 10 August 1993, WHO E16-445-11, 19

Einstein world record, Spider-Man physics, quantum films and cakes

By Sarah Tesh and James Dacey

A world-record-breaking hoard of Albert Einsteins invaded Toronto in Canada on Tuesday 28 March. 404 people gathered in the city’s MaRS Discovery District dressed in the genius’s quintessential blazer and tie, and sporting bushy white wigs and fluffy mustaches. As well as breaking the previous Guinness World Record of 99 Einsteins, the gathering kicked off this year’s Next Einstein Competition. The online contest invites the public to submit ideas that can make the world a better place and awards the winner $10,000 to help them realize it.

(more…)

Quantum memory is made from doped silicon

Quantum information has been stored in a single atom of phosphorus embedded in a silicon crystal – and then retrieved at a later time. The quantum memory was made by physicists in Australia who say that this kind of memory could be an important ingredient in silicon-based quantum computers with the potential to be more scalable, compact and easier to mass-produce than devices based on rival technologies.

Long-term storage in classical computers is straightforward; digital bits are simply copied from the processor to a rotating magnetic disk or other suitable medium. But quantum computers, which encode data in the form of quantum bits, or qubits, face a fundamental obstacle – the no-cloning theorem dictates that it is impossible to copy the state of a qubit or any other quantum object.

A quantum memory instead involves transferring a quantum state from one qubit to another, so erasing the state of the first qubit in the process. Because the second qubit – the “memory qubit” – is chosen to be more resilient to external sources of electrical or magnetic interference that would otherwise destroy quantum coherence, this transfer could enable computations that rely on information being parked temporarily while other data are processed. However, the first qubit – the “processing qubit” – also plays its part. Being less resilient to interference, it is therefore also more responsive to deliberate electromagnetic stimulation, and as such is used to read and write data.

Extra electron

In the latest work, Andrea Morello of the University of New South Wales and colleagues have exploited a natural two-qubit system by doping silicon with atoms of phosphorous. Silicon atoms contain four electrons in their outer shells. This means that each electron forms a covalent bond with a neighbouring atom and this gives silicon its crystal structure. Phosphorus, which is next to silicon in the periodic table, adds an extra positive charge to the lattice, so attracting an extra electron. This effectively creates a hydrogen atom in which the less magnetically sensitive nuclear spin forms the memory qubit, while the electron spin acts as the processing qubit.

Silicon’s crystal properties means that an electron confined in its lattice has a very narrow spatial wavefunction – being just a few nanometres wide. As Morello points out, this means having to manipulate a solid-state circuit at close to the atomic scale, something, he says, that “is not a cup of tea in a university research lab”. But silicon’s long quantum-coherence times gives it a major advantage over rival technologies – as does the ease at which silicon devices can be manufactured. This is because its spins are naturally insensitive to electric noise and can be made very insensitive to magnetic noise by enriching silicon so that its only isotope with nonzero nuclear spin – silicon-29 – is almost entirely absent.

In their experiment, Morello and colleagues implanted phosphorus atoms into a 100 × 100 nm² region of a 900 nm-thick layer of enriched silicon. They set the initial state of the phosphorus electron spin using a microwave antenna fabricated on top of the silicon chip. That spin state is then transferred to and from the nucleus using a series of radio-frequency pulses from the same antenna. To read out the value of the electron spin, they created a single electron transistor from aluminium electrodes fabricated on the chip. The transistor is turned on if the electron escapes the phosphorus nucleus, which only happens when it is in its (high-energy) spin-up state.

Remarkably long time

The researchers found they could transfer the spin state of the phosphorus electron to the nucleus and keep it there for up to 80 ms – “a remarkably long time in the solid state,” says Morello – before transferring it back to the electron and reading it out. Unfortunately, they found that the electron’s final state only matched its initial state around 80% of the time – a fidelity that fell far short of the 99% possible when operating the electron and nuclear qubits separately. They believe this is caused by a shift in the electron’s resonance frequency after they turn on the radio-frequency pulses, and say that they will now work to eliminate this shift.

Morello’s group is not the first to demonstrate quantum memory in silicon. Back in 2008, John Morton, then at Oxford University, and colleagues did so by collectively manipulating the spin states of billions of phosphorus atoms in a large piece of silicon crystal. But Morton says the latest work is important because in a large-scale quantum computer, information must be encoded into individual qubits. He notes that the hardest part of the experiment was reading out the electron spin state, the Australian group having first developed its detection technique in 2010.

Morton, now at University College London, concedes it “remains an open question” among physicists about how useful this kind of memory would be, given doubts about the length of time that electrons would be “idle” as opposed to processing, and also given the need for very high fidelities. One “very exciting” future avenue of research, he says, is to use nuclear spins that are more weakly coupled to the electron spin, such as the spin-1/2 nuclei of silicon-29 in naturally occurring silicon. Being less affected by the electron’s removal during the read-out process, they could potentially operate with fewer interruptions than the phosphorus nuclei.

The research is reported in Quantum Science and Technology.

In this video, Andrea Morello answers the question “Why use silicon qubits for quantum computing?“.

Flash Physics: Alexei Abrikosov dies, SpaceX lands a rocket, long nanotubes are excellent heat conductors

Superconductivity pioneer Alexei Abrikosov dies at 88

The Nobel laureate Alexei Abrikosov has died at the age of 88. Born in Moscow in 1928, Abrikosov completed an undergraduate degree in physics at Moscow State University in 1948 before studying for a PhD in physics at the Institute for Physical Problems (IIP) in Moscow, graduating in 1951. Following a stint as a researcher at the IIP, in 1965 Abrikosov moved to the Landau Institute for Theoretical Physics until 1988. After two years as director of the Institute for High Pressure Physics, he then moved to Argonne National Laboratory in the US in 1991 where he remained for the rest of his career. Abrikosov made pioneering contributions to the theory of superconductivity. The theory of type-I superconductors – in which the material completely expels a magnetic field – was developed in the 1950s by the US scientists John Bardeen, Leon Cooper and Robert Schrieffer, for which the trio were awarded the Nobel Prize for Physics in 1972. Abrikosov together with Vitaly Ginzburg of the P N Lebedev Physical Institute in Moscow, developed a theory for “type-II” superconducting materials in which superconductivity and magnetism can co-exist. In 2003, Abrikosov shared the Nobel Prize for Physics together with Ginzburg and Anthony Leggett of the University of Illinois at Urbana “for their pioneering contributions to the theory of superconductors and superfluidity”.

SpaceX relaunches and lands a Falcon 9 rocket

Photograph of the SpaceX Falcon 9 rocket launch as part of the SES-10 mission — The used first stage of a SpaceX Falcon 9 rocket was successfully relaunched. (Courtesy: SpaceX)

A used Falcon 9 first stage has been successfully relaunched and landed as part of a recent SpaceX mission. In the past, rockets have traditionally been one use only. But in this case the segment had previously been used 11 months ago on a supply run to the International Space Station. The current mission, launched from Florida’s Kennedy Space Center in the US at 18:27 EDT on 30 March, saw it assist in delivering SES-10, a commercial communications satellite, into geostationary orbit. The rocket segment was also successfully landed on a barge in the Atlantic. Containing nine Merlin engines and aluminium-lithium alloy tanks of liquid oxygen and rocket-grade kerosene propellant, the first stage represents about 80% of a Falcon 9 launch cost. Therefore, the successful relaunch and recovery is an important milestone for SpaceX and may lead to significant cost savings. “This is going to be, hopefully, a huge revolution in spaceflight,” says SpaceX chief executive Elon Musk. Although NASA’s space-shuttle system was partially reusable, the SpaceX mission is the world’s first re-flight of an orbital class rocket.

Long nanotubes are excellent heat conductors

The thermal conductivity of singled-walled carbon nanotubes (SWCNTs) increases with their length on scales of several millimetres, according to physicists in Taiwan. Carbon nanotubes have walls that are just one atom thick and it was already known that their thermal conductance increases with length on microscopic scales. This contradicts Fourier’s law of heat conduction, which says that the thermal conductivity is an intrinsic material property that is independent of the shape of a sample. Calculations had suggested that the thermal conductivity of defect-free SWCNTs would increase up to millimetre lengths, however it has been very difficult to both calculate and measure conductivities of long SWCNTs. Now, Victor Lee, Chih-Wei Chang and colleagues at the National Taiwan University in Taipei have come up with a way of measuring the thermal conductivity of SWCNTs with lengths between 4 μm and 1.039 mm. They found that the thermal conductivity increases with the length of the SWCNT and that some 1 mm long samples had conductivities that are approximately four times higher than diamond or graphene – materials that are both known for their very high thermal conductivity. The physicists say that their findings suggest that the heat-carrying capacity of long-wavelength lattice vibrations (phonons) play an important role in the thermal properties of low-dimensional systems such as SWCNTs. The result, which is reported in Physical Review Letters, could lead to the development of high-effective heat-management systems for tiny systems such as computer chips.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on a new silicon qubit.

Asteroid ‘Bee-Zed’ shares a retrograde orbit with Jupiter

A possible refugee from the Oort Cloud that is revolving backwards around the Sun is reshaping our understanding of orbital dynamics by sharing an orbit with the giant planet Jupiter.

The object, known as 2015 BZ₅₀₉ or “Bee-Zed” for short, was first spotted by the Pan-STARRS survey and followed up by a team lead by Paul Wiegert of the University of Western Ontario in Canada using the Large Binocular Telescope in Arizona. If we were to look down at the solar system from above the Sun’s north pole, we would see the vast majority of objects including all the planets orbiting in a counterclockwise fashion. Bee-Zed bucks this trend: it orbits clockwise in retrograde fashion.

Although rare, retrograde orbits per se are not mysterious. What really makes Bee-Zed stand out is that it also shares Jupiter’s orbit, in a 1:–1 resonance (the minus sign indicating retrograde motion). But instead of being kicked out of the orbit by the gas giant, the asteroid is in a configuration that has allowed it to remain stable for millions of years while never colliding with Jupiter.

Shared orbit

Jupiter is no stranger to sharing its orbit. Trapped at the L4 and L5 Lagrangian points, 60° ahead and behind Jupiter, respectively, are two swarms of asteroids known as the Trojans that move prograde – in the same direction as Jupiter.

Bee-Zed is a kind of “anti-Trojan”, whose existence was predicted by Helena Morais of São Paulo State University in Brazil and Fathi Namouni of the Côte d’Azur Observatory in France, two years before its discovery. Its orbit is inclined by 163° to the plane of the ecliptic, cutting across Jupiter’s path every six years, but it never gets closer than 176 million kilometres. Jupiter’s gravity perturbs its orbit during each encounter, but “these nudges are quite gentle because the two don’t get very close,” Wiegert told physicsworld.com. Ultimately the perturbations cancel each other out, with the net result being that Bee-Zed remains on its orbital path.

Jupiter is very dominant in the solar system and can grab hold of objects and move them to new areas that can be safe or potentially hazardous
Jonathan Horner, University of Southern Queensland

Wiegert suspects that Bee-Zed was once a comet that originated from the Oort Cloud, from where comets can come from any direction, often with highly inclined and retrograde orbits. The most famous comet in history, Halley’s comet, has a retrograde orbit and is suspected to be an interloper from the Oort Cloud.

Comet puzzle

How comets like Halley transition from very long-period orbits to the relatively short periods they have today is uncertain, says Jonathan Horner of the University of Southern Queensland, Australia, who was not part of the research. If Wiegert is correct about Bee-Zed being a former Halley-like comet, then “it strikes me that this object could be part of the answer to that puzzle,” says Horner.

Another possibility is that Bee-Zed was once a member of the 6000 Trojan asteroids, but was scattered away during the early history of the solar system when Jupiter and Saturn migrated outwards and fell into a brief orbital resonance.

“It’s possible that a few objects were scattered onto retrograde orbits and were then re-captured by Jupiter as part of that migration,” says Horner. A third possibility is the Kozai mechanism, in which perturbations from outer planets can reduce the eccentricity and increase the inclination of an asteroid’s orbit to the point that its orbit flips over.

More retrograde Trojans

Wiegert suspects that Jupiter may possess more retrograde co-orbital asteroids and comets waiting to be discovered, “but there’s unlikely to be as many as the prograde Trojans simply because retrograde orbits are much rarer,” he says, adding that he “would not be surprised if we discover more of them around different planets, including Earth”.

The co-orbital resonance with Earth should prevent such asteroids from impacting our planet, but Jupiter also has a role to play in the rate of impacts on Earth. In a series of papers published between 2008 and 2010, Horner and the late Barrie Jones of the Open University found that Jupiter is just as likely to fling objects towards us as it is to sweep them up or eject them out of the solar system. The presence of retrograde co-orbitals gives Jupiter another way of capturing incoming objects, but “I don’t think it adds any credence to the idea that Jupiter is our protector,” says Horner. “Jupiter is very dominant in the solar system and can grab hold of objects and move them to new areas that can be safe or potentially hazardous.”

The discovery of Bee-Zed also raises implications for exoplanet research. Although two Jupiter-sized bodies could not be co-orbital, “it’s not unreasonable for a small planet to exist in a retrograde orbit next to a Jupiter-sized planet,” says Wiegert. Although retrograde exoplanets have previously been discovered, they are not co-orbiting with other planets; however, Wiegert suggests that it’s worth looking out for such planetary duos.

The research is described in Nature.

Flash Physics: US reactor to make molybdenum-99, radiotherapy side effects, entangled photons from two places

US university reactor to make molybdenum-99

The University of Missouri Research Reactor (MURR) has unveiled plans to make molybdenum-99. This is used to make the medical-imaging isotope technetium-99m, which could soon be in short supply in North America because of the upcoming closure of a reactor in Canada. MURR has filed an application with the US Nuclear Regulatory Commission to make the isotope using technology developed by US-based General Atomics. This will involve placing low enriched uranium targets inside the reactor and then extracting molybdenum-99 from the irradiated targets. The molybdenum-99, which has a half-life of 66 days, will then be transported 1600 km to Ottawa, where it will be further purified by Canada-based Nordion. The isotope is then distributed to radiopharmaceutical manufacturers, who integrate the molybdenum into technetium-99m generators, which are shipped to hospitals. The plan is a response to possible shortages of molybdenum-99 that could occur once the NRU reactor in Chalk River, Canada, shuts down in March 2018. NRU currently makes most of the molybdenum-99 used in North America and officials at MURR say their proposal could supply nearly half of the US demand for the isotope.

Shining a light on radiotherapy side effects

SFDI images of breast tissue damage by radiation therapy. (Courtesy: Anaïs Leproux, Beckman Laser Institute and Medical Clinic)

An LED-based device allows scientists to monitor skin damage caused by radiotherapy during breast-cancer treatment. Patients often undergo radiation therapy after surgery or chemotherapy to kill any remaining cancerous cells. Unfortunately, the treatment can cause significant skin afflictions including irritation, peeling, blistering, permanent discolouration and tissue thickening. There are currently no methods to predict the severity of reactions, so researchers at the University of California, Irvine (UC Irvine) in the US have begun using Spatial Frequency Domain Imaging (SFDI) devices to monitor and characterize the damage. SFDI uses the fact that light absorbs and scatters to varying degrees depending upon the properties of the target object. Detecting the reflected light gives information about those properties. In the current work, Anaïs Leproux and colleagues are using an SFDI device, originally developed by David Cuccia, formally of UC Irvine and founder of Modulated Imaging. To monitor breast tissues, the team use low-power, LED light of eight visible to near-infrared wavelengths. By shining the light in certain patterns using a digital micro-mirror, a camera can detect varying reflectance more accurately. “Since we use several wavelengths of light, we perform spectroscopy and obtain the content of melanin, tissue hemoglobin, in the de-oxygenated and oxygenated state, from which we can calculate the total blood volume and oxygen saturation in the tissue,” says Leproux. The non-invasive technique measures 3–5 mm into the skin. The team addressed concerns about exposing skin to additional radiation by calculating that 10 measurements is the equivalent of two seconds in the sun. They hope that by characterizing and monitoring the skin damage, they can gain a better understanding of the processes involved and potentially predict patients’ reactions. The work is being presented at next week’s OSA Biophotonics Congress: Optics in the Life Sciences meeting in San Diego, California.

Entangled photons created in two different places

Photons created in entangled pairs in a nonlinear crystal can emerge at two different points in space, say physicists in the UK who have studied a special case of a process called spontaneous parametric down-conversion (SPDC). Their finding contradicts a general assumption that such photons are created at the same place in the crystal. SPDC involves firing higher-energy photons into a special type of crystal, which results in the production of two lower-energy photons. This is a quantum-mechanical process and the two photons emerge in an entangled state, which means that as they fly off in different directions they maintain a relationship that is stronger than that allowed by classical physics. Such entangled pairs can then be used in a number of applications including quantum computing and quantum cryptography. Kayn Forbes, Jack Ford and David Andrews of the University of East Anglia looked at a specific type of SPDC called degenerate down-conversion in which the two electrons have the same energy. “Until now, it has been assumed that such paired photons come from the same location,” says Andrews. The trio identified a process involving the propagation of virtual photons in the crystal that results in photons being emitted from two different places. Andrews describes this as “a new positional uncertainty of a fundamental quantum origin,” adding: “Everything has a certain quantum ‘fuzziness’ to it, and photons are not the hard little bullets of light that are popularly imagined.” The study will be described in Physical Review Letters.

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics.

Leadership lessons learnt in the lab

Much is written about the shortage of physics graduates entering teaching, about how many children are never taught physics by a subject-specialist and about the need for more pupils to pursue physics beyond school. But there is another area of crisis in schools and that is leadership. Filling leadership posts is becoming increasingly challenging, especially at the top of the profession. Now is a time full of opportunities and for those with the potential and the skills, leadership in schools could be the perfect career path.

There are opportunities for the full range of physics graduates in teaching, but for those with research or postgraduate experience the prospects may be even better. Reflecting on my own career, the PhD itself wasn’t the key factor in helping me move up the different levels of the education profession. Instead it was the range of skills gained during that postgraduate degree that laid the foundations for leadership success.

After graduating in 1990 I spent three years doing a PhD in particle physics at the University of Birmingham, UK, while working on the OPAL experiment at the Large Electron–Positron Collider at the CERN particle-physics laboratory in Geneva, Switzerland. After receiving my doctorate, I trained to be a teacher for a year before returning to do a postdoctoral degree in biophysics. Three years later, I began my teaching career in a challenging comprehensive (secondary) school. Within a year or so, I had my first low-level leadership role as an assistant headteacher in a large school, reaching headship four years ago.

Despite leaving research for a full-time career as an educator, it was my experience while still a part of research teams that equipped me with key skills and ultimately helped forge my leadership. At the heart of my research life was the teamwork necessary for the functioning of any experimental project. The size of a team varied over my research life, from small teams of three to large detector groups at CERN. A common factor in any of these settings that amazed me, and still does, was the level of democracy and inclusiveness shown within the team. Young, inexperienced voices were heard and given the opportunity to speak by those with years of expertise, acknowledging that age on its own was no guarantee of creativity and innovation. While the implicit hierarchy was always there – maintained by respect for those above you – everyone felt valued and a part of something bigger.

The lessons learnt during that time have served me well throughout my school leadership career. Collaborative approaches within leadership engender shared ownership and this, in turn, ensures all those in a team feel valued. Treating those who work for you as intellectual equals produces commitment, while failure to do so produces resentment. The best leaders in education know this, and they share their authority, invest in their colleagues and place faith in the ability of others. The worst exercise power, alienate their colleagues and encourage division rather than unity.

But there are a range of other skills developed in my research years that are worth mentioning. Effective school leaders must be analytical. Though much of school leadership is about “soft skills”, and there is still a great deal that is analytical. Judging pupil performance and teacher effectiveness, handling budgets and writing timetables all require a logical and analytical mind. As the job often entails having to deal with challenging “human” issues involving children, parents and staff, one benefits from a calm, rational and analytical approach. Schools themselves operate within legal, social and technical frameworks and dealing with the requirements of inspections, legislation and even school-management systems all benefit from detached and abstract approaches often found in the world of research.

School leaders must also be extremely comfortable with data. Don’t get me wrong, I would not suggest that the data processing required in a school equates to that required at the Large Hadron Collider, but the ability to confidently and reliably handle and interpret large data sets is a key skill of a leader in education. Many, if not most, schools are data-driven and mastery of data analysis and statistics will give you a distinct advantage over colleagues with less experience in the area. Data are the lifeblood of schools and, though often shunned as the impersonal and regrettable side of the profession, they are at the heart of education and unlikely to take a back seat any time soon. Indeed, I recall a meeting with a school inspector during which we discussed the school’s progress data. I was able to illustrate and argue points using a range of statistical tools that are rarely found in an inspector’s tool kit. This helped my school through an inspection and did my career no harm at all.

Throughout my postgraduate career, I also honed my presentation skills. From my first talk at CERN during the first term of my PhD, through to lectures as a postdoc, I spent a lot of time planning and delivering talks to expert audiences both small and large. The ability to talk with confidence to a range of audiences is a key skill of school leaders. Whether you are addressing your science department, a whole body of staff or 300 parents, you need the confidence and experience to speak eloquently and convincingly. You are judged by this – you may well be the finest school manager, but fail in front of a critical audience and your credibility is out of the window. Allied to this is the ability to communicate complex ideas. Physics is complex and even with fellow physicists you will surely have to explain your own niche areas. Many issues in schools are extremely complex, made more so by the simple fact that they do not obey the laws of physics. So while you may not be explaining quantum field theory to a parent, I would say that explaining the latest guidance from the UK Department of Education on measuring progress to 100 parents comes a close second.

Having gone through some of the reasons that school leadership offers opportunities for physicists I should issue a caveat or two. Your teams will rarely contain others with backgrounds in physics, even if you are running a science department, so don’t be surprised if you are the only physicist in the room. We are trained in a unique discipline and we do tend to think in a particular way; do not expect your colleagues to think like you or necessarily even understand. Physicists have the potential to make great school leaders, but I wouldn’t like to see a school run by half a dozen of them! Your colleagues will be experienced, intelligent professionals, with equally valuable but potentially very different skill-sets to those you possess. It is this diversity – which is a strength and should always be encouraged – that makes school leadership teams work.

Every child, teacher, parent and community is unique, as is every situation; a consequence of which is that every leadership challenge is distinctive. Coupled to this is the fact that every school leader is unique when it comes to their own values, beliefs, experience, knowledge and expertise. Consequently there is no simple checklist to determine whether you could be a successful school leader, but for those pursuing postgraduate physics and looking for a meaningful career beyond universities and laboratories, school leadership may offer a rewarding future.

Web life: Quantum Frontiers

So what is the site about?

Quantum-based technologies have undergone something of a revolution in the past decade or so. With that in mind, the National Science Foundation in the US set up “Physics Frontiers Centers”, bringing together research groups and teams from across the country, with an aim to “foster major breakthroughs at the intellectual frontiers of physics”. In 2012 the Institute for Quantum Information and Matter (IQIM) at the California Institute of Technology (Caltech) joined the group, and its members launched the blog Quantum Frontiers in July that year. The institute focuses on “physical systems in which the weirdness of the quantum world becomes manifest on macroscopic scales” and the research – and therefore the blog – covers everything from mechanical quantum systems to quantum information and optics, nanotechnology and of course, quantum computation. The blog is run and written by IQIM researchers and students, but with a few core contributors including IQIM director John Preskill and PhD student Nicole Yunger Halpern.

What are some of the topics covered?

Pretty much anything and everything quantum-physics-related that the team is working on gets covered. A lot of the blogs are based on events, conferences and talks that the authors are attending, as well as timely posts such as the “mechanics of thanksgiving”. The blog is also cleverly divided into five main sections: experiments, theory, reflections (where “distinguished guests reflect on their work and the world of science”), real science (which focuses on the work being done at IQIM by teachers and students) and finally the “expert’s corner”, where you, the reader, can pose questions to any of the researchers about their work. What makes Quantum Frontiers engaging is that most authors discuss how they got involved in the field or talk candidly about a current project, lifting the veil on academic life.

Who is it aimed at?

To some extent, anyone with a healthy interest in how quantum technologies are being developed would do well to read the blog. That being said, the posts are fairly detailed and technical, so you may be slightly bewildered with some of the details. “We hope that the posts to come will be long on inspiration, even if short on information about how to do your homework,” wrote Preskill in his first post and on that, they have been successful.

Can you give me a sample quote?

From a 31 January post titled “Hamiltonian: An American Musical (without Americana or music)”: “Critics are raving about it. Barack Obama gave a speech about it. It’s propelled two books onto bestseller lists. Committees have showered more awards on it than clouds have showered rain on California this past decade. What is it? The Hamiltonian, represented by Ĥ. It’s an operator (a mathematical object) that basically represents a system’s energy. Hamiltonians characterize systems classical and quantum, from a brick in a Broadway theatre to the photons that form a spotlight. Ĥ determines how a system evolves, or changes in time. I lied: Obama didn’t give a speech about the Hamiltonian. He gave a speech about Hamilton: An American Musical, which spotlights 18th-century revolutionary Alexander Hamilton. Alexander conceived the US national bank. He nurtured the economy as our first secretary of the Treasury. The year after Alexander Hamilton died, William Rowan Hamilton was born. Rowan conceived 4D numbers called quaternions. He nurtured the style of physics, Hamiltonian mechanics, used to model quantum systems today. Hamilton tickets sell out despite costing more than $1000…Musical fans across the country are applauding Alexander. Hamilton forbid that William Rowan should envy him. Let’s celebrate Hamiltonians.”

Enjoy the rest of the March 2017 issue of Physics World in our digital magazine or via the Physics World app for any iOS or Android smartphone or tablet. Membership of the Institute of Physics required

Laser pulse changes atomic wire from insulator to metal

Wires just three atoms wide that change from being insulators to electrical conductors – and then back again – when struck by a laser pulse have been created by researchers in Germany. The team has shown that the phase transitions can occur as fast as quantum mechanics allows, something that was not previously thought possible. The technique could prove useful in the study of a wide range of systems including how proteins rearrange themselves.

Phase transitions are ubiquitous in all forms of matter. If energy is added to or removed from a system, the most stable state may change: ice melts to liquid water when heated, for example. Subtler phase transitions can also occur within one state: solid iron can exist in several different crystal structures, for example. The speed at which such phase transitions can occur normally depends on how fast energy can enter the crystal lattice, stimulating random motion of the atoms, for example by scattering of electrons. Previous research by Michael Horn-von Hoegen of the University of Duisburg-Essen in Germany and others has shown that this can occur within 2–5 ps in bulk materials, but takes longer at surfaces because of weak coupling between bulk and surface vibrational modes.

In the new research, however, Horn-von Hoegen and colleagues have shown that surface phase transitions can occur much faster than this. The team studied indium atoms adsorbed onto silicon surfaces. At high temperatures the atoms self-assemble into metallic wires just three atoms wide, whereas at temperatures below 125 K, the wires break up and the surface becomes an insulator.

Diffraction pattern

The researchers first cooled their indium-on-silicon sample to 30 K and measured the electron diffraction pattern of the insulating surface. They then hit the surface with near-infrared laser pulses, causing the surface to warm up. After a variable time delay, they used electron pulses to see how the diffraction pattern had changed. For delays longer than 350 fs, the diffraction pattern of the insulating state was replaced by that of the metallic wires.

“We can answer the question ‘How fast do the atoms move and how fast are they accelerated during this displace excitation mechanism?'” explains Horn-von Hoegen. “It’s something like a trillion times faster than the acceleration you can obtain with a racing car.” The speed increased with the power of the laser pulse up to a certain point, above which it remained constant. “That is then the so-called quantum limit,” says Horn-von Hoegen: “The system cannot react any faster.”

Computational modelling by theoreticians at the University of Paderborn suggests that indium electrons are photoexcited to higher energy levels in the heating process. “We populate electronic states that weaken some bonds or strengthen non-existing bonds,” explains Horn-von Hoegen. This drives the atomic motion during the phase transition. Furthermore, as the atoms move, the electronic band structure of the electron system changes. Incredibly, all of this happens while the atoms are still cold: “Only on a timescale a factor of six to 10 slower does the lattice heat up,” he explains.

Metastable metal

The theoreticians calculated the overall potential energy of the system for different electronic excitations. From this they extracted the conversion time from the insulating to the metallic state, which matched the observed value. After the transition, the cold system lacks the activation energy needed to return to the insulating state, so remains in the metastable metallic state for about 10 ns, which team member Tim Frigge describes as “eternity” for such an atomic system. Despite this delay, the system can be thought of as the fastest electronic switch ever observed, However, Horn-von Hoegen stresses the paper is fundamental research: “I think the idea that these atomic wires will at some point be used as interconnects in ultrafast optical switches should not be taken too seriously,” he admits.

Claus Ropers of the University of Göttingen in Germany is impressed: “There’s not that much structural-dynamics research yet conducted at surfaces because the technology is still being developed,” he says. “These authors have made significant contributions in the past, and in the combination of theoretical and experimental work, this is probably the paper where they’ve put together the most comprehensive understanding of a particular transition.”

Bradley Siwick of McGill University in Canada agrees: “It’s probably the most exciting and the best work yet done on ultrafast dynamics in a surface system,” he says. “We [the scientific community] can watch atoms, follow their motion on the fastest timescales open to them, and see what effect those rearrangements have on the electronic properties of materials. This is a remarkable step forward. This is just the tip of the iceberg: experiments like this could allow you to follow the structure of a protein in a crystal as a function of time and determine how that protein performs its function at the atomic level.”

The research is described in Nature.

Flash Physics: Stars born near black holes, stormy superfluids, AAAS asks Trump to engage with scientists

Stars born as supermassive black holes devour their surroundings

Stars are forming within the material blasted out by supermassive black holes. This extreme-environment stellar formation has been seen by astronomers using the European Space Observatory‘s (ESO) Very Large Telescope (VLT). Supermassive black holes exist at the centre of most galaxies and emit extremely powerful outflows of energy and material as they devour surrounding matter. “Astronomers have thought for a while that conditions within these outflows could be right for star formation,” says team leader Roberto Maiolino of the University of Cambridge in the UK, “but no one has seen it actually happening as it’s a very difficult observation.” The group used the VLT’s MUSE and X-shooter instruments to study the colossal jets emitting from a galaxy’s supermassive black hole 600 million light-years from Earth. By searching for the characteristic radiation signature of young stars, Maiolino and colleagues identified an infant stellar population within the outflow, containing stars less than a few tens of millions of years old. Due to the outflows’ extreme environment and fast-moving material, the young stars are hotter and brighter than typical stars and travelling at high velocity away from the galaxy centre. “The stars that form in the wind close to the galaxy centre might slow down and even start heading back inwards,” explains team member Helen Russell, “but the stars that form further out in the flow experience less deceleration and can even fly off out of the galaxy altogether.” The discovery, published in Nature, could lead to a better understanding of galaxy evolution.

Stormy superfluids could have boundary layers

Storm brewing: Computer simulation of vortices (red) within a superfluid flowing past a rough surface (yellow) showing a boundary layer. (Courtesy: Nick Parker)

Despite having no viscosity, a superfluid will form a storm-like boundary layer as it flows along a rough solid surface. That is the surprising conclusion of George Stagg, Nick Parker and Carlo Barenghi of the University of Newcastle in the UK, who have done computer simulations of superfluid flow. A superfluid is a quantum state of matter that occurs at very low temperatures and is characterized by viscous free flow that, once started, can persist indefinitely. When an ordinary fluid flows along a surface, the liquid nearest the surface is slowed down by friction and this braking force is transmitted into the bulk of the fluid by its viscosity. This creates a boundary layer in which the flow increases gradually to that of the bulk fluid – something that should not occur in a superfluid with zero viscosity. Now, the Newcastle trio have calculated that vortices created when a superfluid flows over a rough surface could form a similar boundary layer. “Our computer simulations show that, remarkably, boundary layers can arise in viscosity-free superfluids, in a distinctly quantum mechanical form,” says Parker. While physicists expect these vortices to occur, they were surprised that their simulations suggest that the vortices tangle together tightly to form a swirling-storm-like layer that “sticks” to the surface. Furthermore, the flow velocity in the boundary layer increases smoothly to the bulk value – just like a conventional boundary layer. “This result points to the universality of boundary layers and sheds new light on the deep connection between superfluids and ordinary fluids,” says Parker. The simulations are described in Physical Review Letters.

AAAS asks Trump to engage with the scientific community on climate change

Rush Holt, the chief executive of the American Association for the Advancement of Science, has called on president Donald Trump and US policymakers to address the risks of climate change by engaging with the scientific community. The statement comes after Trump signed an executive order concerning the US Environmental Protection Agency (EPA) that aims to roll back current limits on carbon emissions. The order also calls for a review of restrictions on coal mining on federal land and a review of a policy that considers the “social cost of carbon” in the framing of federal regulations. “The scientific evidence is clear: climate change is happening – primarily due to human activities – and already impacting people and our environment,” says Holt, who is a physicist. “We encourage the White House and Congress to support the evidence on climate change, and welcome opportunities to bring scientists to meet with policymakers to discuss the state of the science, the degree of scientific understanding on climate change, and other areas of concern and interest.”

You can find all our daily Flash Physics posts in the website’s news section, as well as on Twitter and Facebook using #FlashPhysics. Tune in to physicsworld.com later today to read today’s extensive news story on a how light can change the structure of nanowires.

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