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Lasers go to the dark side

A newly designed compact tunable laser has demonstrated high-quality emission while boasting subwavelength thickness. When the gain medium is excited, the lasing energy is stored in a surface-bound cavity mode (dark-mode), as opposed to the traditional un-bound, radiating mode. Here, the strong, tightly confined light can be used in sensing applications. Alternatively, the light can be coupled to either free-space or surface modes by adjusting the position of small scattering elements on the surface that behave as an electromagnetic metasurface, coupling the dark-mode lasing state to radiation.

A lab-on-a-chip is the ultimate goal for many researchers, and one important component is a small but efficient laser. Many attempts at creating such a device have been made, and include the use of photonic crystals, ring resonators and plasmonic arrays. However, all of these suffer from either wavelength-limited miniaturization, or high material losses and low quality (Q-) factors. In all cases, radiation damping lowers the Q-factor considerably.

A team of researchers at the Institute of Electronic Structure and Laser, Heraklion, Greece and Ames Laboratory and Department of Physics and Astronomy, Iowa, USA, have found a way around these problems. They create a linear grating of silver strips, where the space between the strips is filled by a high-index dielectric with a gain medium embedded in it. This periodically modulated thin dielectric film supports resonant, dark-bound states. The spacing of the grating is carefully chosen to match the emission band of the gain medium, and to provide the highest Q-factor. This structure is much thinner than the emission wavelength, and does not suffer so much from material damping as it is made of mostly dielectric, not metal.

When the gain medium is pumped by an external light source, the energy accumulates in the gain medium and lasing, i.e., stimulated emission, occurs directly in the dark bound state of the laser. By definition this mode does not radiate to free space, eliminating radiative losses. Then, by including small non-resonant scatterers on the surface of the grating, which collectively act as an electromagnetic metasurface, the energy in the dark mode is scattered to free space in the form of a wave, creating the optical laser beam output. This approach separates the conceptual constituents of lasing action, cavity resonance and out-coupling to the emitted laser-radiation from one another, and allows the researchers to independently optimize the individual components.

Using this concept, first proposed in an earlier paper, the team, led by Costas Soukoulis, took full advantage of the exotic capabilities of metasurfaces (wavelength-scale periodic arrays that manipulate electromagnetic fields) to affect the shape and properties of the emitted laser beam. They fully characterized possible geometries for the laser through extensive simulations. For example, changing the position of the scatterer between the two silver strips allows control of the Q-factor, lasing threshold, directionality and loss channel (whether the energy is radiated away or stored and eventually lost to Joule heating).

The next challenge the researchers will focus on is the fabrication and experimental realization of such a device. The researchers have already outlined some of the fabrication issues that may be faced, along with potential solutions. For example, the effects of radiative and dissipative loss can be balanced by appropriate adjustments to the geometry. Some simplified geometries are explored, taking into account the presence of a substrate and the possibility of layer-by-layer fabrication.

More information can be found in the research paper here, published in Physical Review B.

Superfluid helium could reveal lightweight WIMPs

A new detector sensitive to low-mass dark matter particles too light for current experiments to see has been proposed by physicists in the US. Built around a bath of superfluid helium-4, the device would use field ionization to spot single helium ions ejected from the superfluid’s surface by colliding weakly interacting massive particles (WIMPs).

The existence of dark matter has been inferred from unexpectedly high stellar and galactic velocities since the early 20th century, and recent observations of gravitational waves have only strengthened the case by ruling out some competing modified-gravity models. Despite the efforts of dozens of experimental collaborations worldwide, dark matter particles have not been detected directly. However, WIMPs are still the dark matter candidate favoured by most physicists.

Unexplored regions

Dark matter surveys conducted until now have focused largely on high-mass particles, and are relatively insensitive to candidates lighter than 10 GeV/c², or about ten times the mass of the proton. Some recent theories have proposed WIMPs with masses below this threshold, so with a view to filling this observational gap, Humphrey Maris, George Seidel and Derek Stein at Brown University conceived a detector model that could extend the lower mass limit by three or four orders of magnitude.

The team decided on ⁴He for the detector mass since it receives more energy per collision than heavier targets, and the low internal radioactivity minimizes false positive results. When dark matter particles interact with the target, recoiling helium atoms are expected to trigger phonons and rotons – quasiparticle excitations – which, in superfluid ⁴He, can propagate without scattering. When these excitations reach the surface of the superfluid, helium atoms are expelled by quantum evaporation.

A similar technique was developed a decade ago by Maris, Seidel and colleagues at Brown University for the HERON neutrino detector. In that experiment, evaporated helium atoms were deposited on a silicon wafer calorimeter suspended above the superfluid, causing a measurable increase in temperature. “This worked fine if a large amount of energy was deposited in the liquid thereby producing many rotons and many atoms,” explains Maris. “But the method was inadequate for the detection of the small number of atoms that would be evaporated if the energy deposit was by a dark matter particle with, for example, a mass of 1 MeV.”

Single-atom sensitivity

The novelty of the new approach lies in the device’s sensitivity to individual atoms. This makes the minimum detectable transferable kinetic energy (the energy imparted to a helium nucleus by a dark matter collision) equal to the binding energy of a helium atom to the liquid. Since no existing large-area calorimeter could be sensitive to such tiny energies, individual helium atoms ejected at low speed can only be detected if they are first accelerated significantly.

The trick proposed by the team at Brown University is to have evaporated atoms pass near to arrays of positively charged, sharp metal tips. Strong local electric fields ionize the helium, and the resulting positive ions are accelerated toward a cathode at energies within the range detectable by current calorimeters.

“The addition of the field ionization opens up the possibility of detecting energy deposits into the helium that are smaller by a factor of about 10,000 than in the previous work that we did. This will make it possible to detect dark matter in a mass range far below what has been previously achieved,” Maris told physicsworld.com. Assuming the Standard Halo Model of dark matter distribution – in which the galaxy is permeated uniformly by WIMPs of a single type, and the local galactic escape velocity is the maximum particle speed allowed – the researchers expect such single-atom sensitivity to translate to a detectable dark matter particle mass of 0.6 MeV/c², or less than a thousandth the mass of a proton.

A modified scheme that could achieve even greater sensitivity has also been presented by the group. Instead of employing bulk helium as the detector mass, a solid crystalline target could be used, which would also be susceptible to phonons initiated by colliding WIMPs. A helium film coating the crystal would exhibit the same excitation-induced quantum evaporation effect but with a lower phonon energy threshold. By lining an ultrapure target crystal with a few monolayers of caesium (to which ⁴He binds especially weakly), an atomically thin film of helium could further lower the WIMP mass sensitivity by orders of magnitude.

Full details of the research are reported in Physical Review Letters.

Targeted therapies tackle resistant tumours

By studying breast cancer tumours in mice, Erkki Ruoslahtiand an international team of scientists have discovered important characteristics of non-responsive tumours that can help restore the targeting and therapeutic effectiveness of a nanoparticle-based cancer treatment.

Previously, the team discovered that this treatment was highly effective at disrupting blood vessels in breast cancer and glioblastoma models. However, tests on mice demonstrated that certain tumours were evasive and resistant to the therapy.

In their latest paper, the scientists compared differences in the vasculature (blood vessel make-up) of the tumours to understand this change in responsiveness. They identified a peptide that may make it possible to specifically target the treatment-resistant tumours (J. Controlled Release 268 49).

Nanoworms disrupt tumour vessels

Previous work by the California-based research team showed that functionalized iron-oxide nanoparticles are potent tumour disrupting agents. The particles, nicknamed nanoworms (NWs) due to their shape, consist of two peptides (the homing peptide GGKRK and _D(KLAKLAK)₂) that respectively target and disrupt the mitochondria of tumour cells. The peptides are displayed on the surface of NWs in large numbers (because the NWs are aggregates of many nanoparticles), which increases their activity.

By looking at responsive mouse tumours under a microscope, the researchers saw that NWs reduced blood vessels in these tumours by 75%. Most of the blood vessels in tumours that responded to treatment also stained positively for lectin (a membrane protein used to detect vessels with blood flow) and CD31 (an antibody used as a general blood vessel marker). However, resistant tumours showed a unique feature: many blood vessels were lectin-positive, but CD31-negative.

Further microscopic investigation indicated that some of the vessels in these tumours might be from human tumour cells, as opposed to the host mouse. However, the scientists found that NW accumulation in non-responsive tumour cells was greatly decreased, even though the homing peptide’s receptor was still expressed at the same level. This finding indicates that an alteration in both CD31-positive and CD31-negative blood vessels has occurred, limiting the homing ability of the nanosystem.

Screening resistant tumours

Since the tumours that are resistant to the NW homing treatment have altered blood vessels, the researchers hypothesized that a different homing peptide (not GGKRK) could restore NW treatment effectiveness.

After screening a phage-displayed peptide library in mice, and sequencing the peptides recovered from non-responsive tumours, the research team saw a high frequency of the RGD peptide, which is used in many different therapies to home in on tumours. This peptide targets integrins, specifically the αvβ3 integrin. As expected, the non-responsive tumours showed higher expression of the β3 integrin subunit than responsive tumours and had elevated expression of β3 mRNA.

Ruoslahti’s team showed that multiple pathways affect a tumour’s ability to resist the vasculature-disrupting NW therapy. Their results also suggest that by using combination therapies, for example NWs functionalized with both GGKRK and RGD peptides, scientists may be able to prevent the development of non-responsive tumours.

Finally, this approach, in which the molecular and cellular basis of resistance in non-responsive tumours was explored, could be applicable to the study of other cancers as well.

Neutrino detector could see radioactive potassium deep within the Earth

A new way of studying radioactive processes deep inside the Earth has been proposed by an international group of physicists. They want to use a next-generation dark matter detector called a gas-filled time projection chamber to detect geoneutrinos produced deep underground by the radioactive decay of potassium – something that existing detectors cannot do.

Rock samples from deep inside Earth’s crust suggest that much of the planet’s internal heat comes from the radioactive decay of unstable isotopes of uranium, thorium, and potassium. These processes give-off neutrinos called geoneutrinos, which travel easily through the Earth and emerge from its surface.

Geoneutrinos from thorium and uranium decay were detected in 2005 by the KamLAND experiment in Japan and in 2010 by Borexino in Italy. The measurements suggested that the decay of these two materials accounts for about half of Earth’s internal heat. But those and other existing detectors cannot see neutrinos from potassium decay. “The neutrinos are too low in energy,” explains Jocelyn Monroe of Royal Holloway, University of London.

Ionized molecules

Monroe and her colleagues, Michael Leyton of Institut de Física d’Altes Energies in Spain and Stephen Dye of the University of Hawaii, predict that a new type of detector, filled with tetrafluoromethane gas, should see the potassium neutrinos. When a neutrino collides with a gas molecule in the detector, the molecule becomes ionized. An electric field within the detector moves the ion towards another part of the detector that produces an amplified light signal.

To see potassium-produced neutrinos, the detector would need to be about 200–500 m³, contain 10 tonnes of gas, and collect data for 5–10 years, says Monroe. They calculated this in part by modelling the neutrino flux through the detector–solar neutrinos, neutrinos produced in nuclear reactors, and geoneutrinos – for three different detector locations. They considered the Kamioka Observatory in Japan, the Gran Sasso experiment in Italy, and SNOLab in Canada.

The detector is based on a prototype dark matter detector that Monroe’s group has been developing for several years. The gas-filled time projection chamber can measure both the energy and direction of an incoming particle, so it can determine if an incoming particle is coming from overhead or from inside Earth. Current dark matter detectors cannot determine the direction of a particle, which means that their data have much higher levels of noise.

Potent greenhouse gas

However, it will take much more planning and engineering to actually carry out the experiment. “The [proposal] has promise,” says William McDonough of the University of Maryland, adding “[but] the devil is in the details”. He cautions against the use of tetrafluoromethane gas, which is a potent greenhouse gas. If the detector leaks, it could cause severe environmental damage, he explains.

The deployment of such a detector is also contingent on the discovery of dark matter, says Monroe. “If dark matter hasn’t been seen 10 years from now, it’s probably going to be a hard sell to build a detector at this scale for geophysics or for particle astrophysics,” she says.

So, at the moment, it’s unclear if such a detector will ever be deployed. But making ambitious proposals is necessary for procuring funding for expensive particle physics experiments, says Giorgio Gratta of Stanford University. “It’s kind of a long process, and it definitely requires [proposals] like this one that don’t have real data,” Gratta says. “It’s useful that the community at large is reminded that the technology exists, in principle.”

The proposal is described in Nature Communications.

Fractured, watery core key to Enceladus’s long-lived ocean

Tidal heating could power Saturn’s moon Enceladus for tens of millions to billions of years if its core is porous and unconsolidated, a new model suggests. The conclusion is based on 3D simulations of tidal friction and heat transport, in which energy is transmitted from the core to the ice shell by advection. As well as accounting for the unexpectedly high heat flux in Enceladus, the model also explains differences in ice thickness between the poles and the equator, and the presence of hydrothermal products in the moon’s water plumes.

Surprisingly warm

Evidence for liquid water under the frozen surface of Enceladus began to mount after the Cassini spacecraft’s first flybys of the remarkable moon in 2005. Further observations suggested that a global ocean separates the moon’s rocky core from its icy shell, but radioactive decay and tidal heating seemed insufficient to explain its persistence.

Writing in Nature Astronomy, Gaël Choblet of the Laboratoire de Planétologie et Géodynamique in Nantes and collaborators in France, USA, the Czech Republic and Germany, have shown that orbital interactions with another of Saturn’s moons, Dione, could generate enough tidal friction within Enceladus to sustain the ocean, but only if the porosity and permeability of the moon’s core fall within certain ranges. Although the body’s small size has made its anomalous warmth difficult to explain until now, it also means that such porosity could have been present in the core since the moon’s formation.

Thin ice

For some combinations of parameters, the group’s simulations predicted polar upwellings of water warmed in the core, where rock and hot water can interact, and corresponding downward flows of cooler water elsewhere. This result is consistent with observations suggesting that the ice is significantly thinner at the poles than at the equator, but it does not explain the asymmetry between the south pole, where the characteristic “tiger stripes” jet plumes of water, and the north pole, which is ancient and inactive. Choblet and colleagues suggest that a small discrepancy in ice behaviour between the poles could have been amplified over time by the concentration of tidal friction in fractures at the south pole.

Reforming Japanese science

By Michael Banks in Tokyo, Japan

Following this morning’s talk at the Tokyo Institute of Technology (as well as a mock earthquake evacuation drill that took place just afterwards), I took the opportunity to visit the Earth-Life Science Institute (ELSI), which is located in a neighbouring building at Tokyo Tech.

Like the Kavli Institute for the Physics and Mathematics of the Universe (IPMU), which I visited yesterday, ELSI is part of the World Premier International Research Center Initiative (WPI).

ELSI began in 2012 and has funding for 10 years from the WPI. There are around 100 people working there, the majority of whom are from outside Japan. Its main aim is to understand how life began on Earth and how that can be applied to the search for life on other planets. It covers a range of disciplines from astrophysics to microbiology.

I sat down with John Hernlund, ELSI’s vice director, and Shawn McGlynn, a principal investigator at the institute. Both are from the US, and Hernlund joined in 2013, becoming the first permanent foreign researcher to work at Tokyo Tech.

Hernlund, who works in astrobiology, notes that one of the fun aspects of working at the institute – apart from the science – is changing how things are done. For example, when the institute was founded it went on a big recruitment drive by placing advertisements in the media. But Hernlund and colleagues quickly discovered that there was no process at the university to do this – it wasn’t how universities in Japan traditionally brought people in.

This resulted in staff members dipping into their own pockets to pay for the advertisements. They eventually got reimbursed, but it took nearly a year to sort it all out and put in place a system should anyone at the university want to follow suit. “This is why reform is so important,” says Hernlund, adding that he hopes such changes will “propagate outside ELSI”.

Given the institute’s funding is guaranteed for only another five years, ELSI is now trying to diversify its income to guarantee its future. Hernlund notes the temptation to even turn away from the WPI programme itself to help the institute become self-sustaining and have more flexibility than it would do if it stayed in the system. One avenue being explored to do this is attracting more private funding.

After visiting ELSI and IPMU it is apparent that these two institutes feel very different from a traditional Japanese physics department. Bringing in foreign researchers – a mandate of the WPI programme – is certainly shaking up the academic system in Japan. It will be interesting to see how much further those reforms go.

How to get your paper noticed

By Matin Durrani in Tokyo, Japan

For physicists, doing research is only the start of the game. With thousands of papers published each year, how do you make sure your latest work stands out from the crowd?

If you’re an established academic, your peers will already know who you are and, provided you can continue getting your papers published in the top journals, your career will carry on hitting the high notes . But if you’re less experienced in the research game, then a good dose of publicity in the mainstream media can give you a great head start – and thankfully the online world can help hugely.

That was the message of a seminar “Science communication in the digital age” given today at Tokyo Institute of Technology by me and my IOP Publishing colleagues Michael Banks (Physics World news editor) and Elaine Tham (associate director for Asia-Pacific). Attended by about 40 students, science communicators and university administrators, the seminar was opened by the president of Tokyo Tech Yoshinao Mishima.

One traditional measure of how well your paper is doing is to note how many times it’s been cited in the reference lists of other papers. But as Elaine pointed out, the digital world offers much more than conventional citation counts. One particularly useful service, now available on all IOP Publishing papers, is Altmetrics.

It captures, in real time, how often a paper has been mentioned by news outlets, policy documents, blogs and other social networks, as well as by other scholarly and non-scholarly sources. By checking your Altmetrics score, which is listed next to the online version of the paper, you can find out what impact your work is having in the wider world.

That’s all very well, I hear you say, but how do you get your work noticed in the first place? There’s no magic solution, of course, but Michael and I offered delegates at Tokyo Tech some top tips for how to get your work spotted and picked up.

Some things are obvious and require little effort: writing about your research on a personal or group website; talking to friends and colleagues; or sending a copy of your paper to those in your field. Others need a bit more work, such as setting up a blog, press-releasing your research, contacting science journalists with story ideas, or creating a short “video abstract” about your paper.

But if you can’t be bothered with any of that, why not just get active on social media? A great photo with a link to your paper can work wonders, especially on Twitter, which academics just love. And best of all it’s free, so you’ve really no excuse.

Investigating the mechanisms of collective cell migration

Collective cell migration – in which cells associated in tight or loose groups move together – plays a central role in embryonic development, wound repair and cancer invasion. As the physical mechanism behind this process remains puzzling, with different aspects to be elucidated, a team of researchers from the University of Arizona has now shown how individual cell biophysics actually dictates the collective behaviour (Biophys. J. 113 1613).

For wound healing, sheet migration is observed. Here, the sheet moves forward as cells at the front edge, the leaders, guide the rest of the cells towards advancing and efficient repairing. As collective behaviour is indeed the result of individual actions, Charles Wolgemuth and his group studied how single epithelial cells influence collective dynamics in wound healing.

Substrate impacts single cell motility
Upon culturing epithelial (MDCK type I and II) cells on different substrates that alter cell-surface adherence (fibronectin, FN, and poly-L-lysine, PL), the authors analysed changes in the cells’ dynamics and morphology. While the two cell types are closely related, the results revealed that highly dynamic MDCK I cells suffered a decrease in area when on PL, suggesting a decrease in adhesion. MDCK II cells, on the other hand, were unaffected by the substrate.

One would expect that cells that move faster when isolated (MDCK I moved faster on FN than on PL, while MDCK II were slower than MDCK I regardless of substrate) would move faster together as well. But when Wolgemuth and his team investigated wound-healing dynamics using scratch assays (creating a “scratch” in the cell monolayer), they found that there was no correspondence between the speed of isolated cells and their collective dynamics.

Are leader cells or jamming the cause?
The dynamics of wound healing is often attributed to leader cells, which stabilize the border and determine the directed migration of the follower cells. The authors showed that the frequency of leader cells did not influence how fast the wound healed, except for MDCK II cells cultured on PL, indicating a correlation between the number of leader cells and coordinated movements in this case.

The researchers next investigated whether collective cell migration is related to a jamming transition, a process in which cells that are packed together tightly can shift to a migratory state as a unit. By taking into consideration a model in which cells display a jamming transition from a solid-like to a fluid-like state (Phys. Rev. X 6 021011), the authors found that MDCK I cells, either on FN or PL, do not represent a jammed system. As such, the physics of jamming cannot be applied for understanding the collective motions of these cells.

Contractile stress imposes collective migration
A model for wound healing described by Lee and Wolgemuth (Biophys J. 111 256) implies that contractile stress, produced by intracellular contraction, is involved in collective migration and can lead to fluid-like flows in an epithelial monolayer. By using this model, the authors simulated a confluent layer of epithelial cells and found that “the contractile stress is the more dominant factor in controlling collective migration speed than the isolated cell velocity”.

Intracellular contractile forces in a cell drive ﬂow of nearby cells

Furthermore, by analysing collective motion in confluent layers of MDCK cells cultured on different substrates, Wolgemuth and his team found out that MDCK I cells on PL had different dynamics in comparison with the other experimental conditions. Such cells undergo highly coordinated motion with larger velocities within the monolayer, enabling them to migrate further than the other cells.

Additionally, the authors used drugs that weaken or strengthen the cytoskeleton to see the effect of contractile stress on MDCK I cells on PL. The results indicated a decreased or increased intralayer speed, respectively, in accordance with the model that showed a “monotonically increasing dependence of intralayer speed on contractile stress” for these cells.

This study reveals important information regarding collective migration dynamics, emphasizing that cell speed is not the driving force that lies behind wound healing but that intracellular contraction is the dominant factor in collective movements. Moreover, the results raise into question the use of wound-healing assays as a measure of cell motility, since substrates can interfere with collective dynamics and should not be used to study single-cell processes.

Celebrating the International Day of Medical Physics

By James Dacey

Today is the International Day of Medical Physics (IDMP), as events around the world raise awareness of the vital work carried out by the profession. Now in its fifth year, the 2017 initiative focuses on issues affecting female patients and the safety of women working in medical physics. The theme was chosen to mark the 150th anniversary of the birth of Marie Curie whose pioneering work on radioactivity still underpins various medical treatments and diagnostics – particularly for cancer patients.

“It is well known that medical physicists have developed imaging and radiotherapy methods that have increased women’s length of life and have improved quality of life,” says John Damilakis of the International Organization of Medical Physics (IOMP), which co-ordinates the annual event. “For example, X-ray mammography for the early diagnosis of breast cancer, dual-energy X-ray absorptiometry for the diagnosis of osteoporosis and brachytherapy methods for gynecologic cancer.”

Celebrations today will focus around three key events – in Jaipur, Kuala Lumpur and Vienna, details of which are provided on the IDMP website. Also on that webpage is a video message from IOMP president Slavic Tabakov recorded against a scenic backdrop in the ancient town of Gabrovo. “One of the long term tasks is the establishment of a full IOMP committee aiming to bring women medical physicists closer together – an important initiative which I fully support,” he says.

You can find further information about the initiative and its goals in this article by my colleague Tami Freeman at Medicalphysicsweb. Here at Physics World we also cover key scientific developments in the medical physics community, such as when I travelled to the Massachusetts General Hospital (MGH) to produce a series of films about proton therapy. This form of treatment can target specific types of tumour with precision, offering an alternative to conventional radiotherapy treatments. Here is a couple of films from that series.

Proton therapy is a truly interdisciplinary field, involving physicists, medical doctors and applied mathematicians in the treatment planning. For a more detailed look at the science and technology of proton beam therapy, check out this free-to-read ebook written by MGH medical physicist Harald Paganetti as part of the Physics World Discovery series. Paganetti evaluates the fundamental science and technology of proton therapy, then outlines some of the current physical, biological, and clinical challenges.

Paganetti is also a board member on the journal Physics in Medicine and Biology (PMB), which is published by IOP Publishing. That broad-scope journal had its 60th anniversary last year and I produced this video report from the birthday celebrations in London. Medical physicists speak about what the field has achieved so far and how it can continue to mature by developing stronger bridges between the physics, medical and biology communities.

Just last week I was back in London recording a series of interviews with PMB board members who spoke about some of the most exciting developments in the field, especially around medical imaging technologies. Those videos will be appearing on this website within the next few weeks. In the meantime, go spread the word: physics knowledge and technologies have a key role to play in contemporary medicine.

RIKEN celebrates its centenary

By Matin Durrani in Wako, Japan

It’s funny where chance encounters can lead.

Earlier this year, I was at a reception for science journalists at the Fenway Park baseball stadium in Boston, US, when I bumped into Jens Wilkinson, who works in the communications team at RIKEN – one of Japan’s biggest research institutions. He encouraged me to visit the lab, which was founded 100 years ago, should I ever find myself in Japan.

And so here I was at RIKEN’s headquarters in Wako, just north of Tokyo, on day two of my trip to gather material for the upcoming Physics World special report on Japan. Wako is home to the largest of RIKEN’s seven campuses, which together employ almost 2000 researchers.

Apart from celebrating its centenary this year, which included an event in downtown Tokyo with none other than Emperor Akihito, RIKEN has been in the news for its discovery of element 113. Created at the RIKEN Nishina Center for Accelerator-Based Sciemce by smashing zinc nuclei into a bismuth target, the element was last year officially named “nihonium” (Nh).

A LEGO model at RIKEN of the classic radionucleide chart, which shows stable and unstable nuclei on a plot of protons versus neutrons — Block by block: a LEGO model at RIKEN of the classic radionucleide chart, which shows stable and unstable nuclei on a plot of protons versus neutrons. (Courtesy: Matin Durrani)

As Kouji Morimoto from RIKEN’s research group for superheavy elements explained to me, nihonium’s name comes from “Nihon” – one of two alternative names for Japan, both of which mean “land of the rising Sun”. The other name – “Nippon” – was not allowed to be given to the new element as it had been used by the Japanese researcher Masataka Ogawa in 1908 to describe an element with an atomic mass of 43 that he thought he’d discovered. Unfortunately, what Ogawa had actually found was what we now call rhenium, which has an atomic mass of 75. And because “nipponium” had been previously used in error, the rules stated it couldn’t be used again. So nihonium it was.

You can see it on the close-up of the LEGO model (right) picked out with a tiny flag.

Putting down a marker: a tiny flag identifies nihonium on the LEGO model at RIKEN.

Naming the element was the least of the RIKEN team’s worries. As Morimoto pointed out, creating nihonium was a huge feat, given that zinc and bismuth nuclei fuse just once in a 100 trillion collisions in their lab. In fact, the experiment took 500 days of beam time and even then the team created just three solitary atoms of nihonium.

Now if you think this kind of research has no relevance to everyday life, you’re wrong. Hiromitsu Haba, who leads RIKEN’s RI applications research group, described how the radioactive isotopes created at its Radioactive Ion Beam Factory (RIBF) are used in everything from pharmaceuticals and industry to engineering and medicine.

One isotope in particular – astatine-211 – is shipped to researchers across Japan who want to see if it can be used to treat cancer. Astatine-211 releases alpha particles with energies that are good at killing tumours, while leaving surrounding tissue more intact than rival beta-particle-emitting radioisotopes.

Photo of the sake brewed with yeast developed at RIKEN — Tasty stuff: the sake brewed with yeast developed at RIKEN. (Courtesy: Matin Durrani)

Haba also mentioned another interesting application of RIKEN’s heavy-ion beams, which is to breed a new kind of yeast that’s been used to create a special kind of sake rice wine. Three types of sake are brewed using the new yeast and have been on sale since 2011. I wonder if they were served to the emperor at RIKEN’s centenary celebrations? It’s one question I forgot to ask…

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Lasers go to the dark side