A storied Russian lab is trying to push the periodic table past its limits—and uncover exotic new elements | Science
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A storied Russian lab is trying to push the periodic table past its limits—and uncover exotic new elements | Science
DUBNA, RUSSIA—From certain angles, the Flerov Laboratory of Nuclear Reactions here looks more like an auto repair shop than a legendary scientific institute. Scientists in dirty blue smocks walk around while an oil pump thumps out a techno beat. Tables are strewn with bolts and cleaning fluids, including a vodka bottle half full of ethanol. And spare parts are everywhere—bins, shelves, whole walls full of metal whatsits in all manner of disrepair.
All that stuff serves the lab’s six particle accelerators, some of which resemble huge mechanical caterpillars, with dozens of tractor-green segments winding through entire rooms. Or multiple rooms: When equipment doesn’t fit, researchers knock holes in walls and thread things through the concrete. Seeing the whole of an accelerator requires some serious gymnastika, scaling perilously steep stairs and dodging anacondas of hanging wires. The pipes you duck under bear warning signs to watch out—not for your head, but for the equipment. At Flerov, particles have the right of way.
Deservedly so. In various iterations, these accelerators have produced nine new elements on the periodic table over the past half-century, including the five heaviest known elements, up to number 118.
The man leading that work is physicist Yuri Oganessian, who has been at Flerov since Nikita Khrushchev signed orders in 1956 to establish a secret nuclear lab in the birch forests here, 2 hours north of Moscow. Oganessian, 85, is a short man with bushy white hair whose voice squeaks when he gets excited. He wanted to study architecture in college until a bureaucratic snafu diverted him into physics. He still misses his first love: “I really need something visual with my science. I feel this deficit.”
Fittingly, no living person has shaped the architecture of the periodic table more than he has, which is why element 118 is called oganesson. And he’s not done yet. To push the table further, the lab has built a new $60 million facility, dubbed the Superheavy Element Factory (SHEF), which will start to hunt for element 119, 120, or both, this spring.
Some scientists argue that finding new elements is not worth the money, especially when those atoms are inherently unstable and will disappear in a blink. “I personally don’t find it exciting, as a scientist, just to produce more short-lived elements,” says Witold Nazarewicz, a physicist who studies nuclear structure at Michigan State University in East Lansing.
But to element hunters, the payoff is compelling. The new elements would extend the table—now seven rows deep—to an eighth row, where some theories predict exotic traits will emerge. Elements in that row might even destroy the table’s very periodicity because chemical and physical properties might not repeat at regular intervals anymore. Pushing further into the eighth row also could answer questions that scientists have wrestled with since Dmitri Mendeleev’s day: How many elements exist? And how far does the table go?
The decision to build the SHEF was tough in some ways. Besides the high cost, constructing the “factory” meant abandoning the old accelerators—which produced so many new elements—to other projects. “Emotionally,” Oganessian says, “it’s not easy to take something [offline] that gave you a lot. But there is no other way forward.”
The heaviest element found in any appreciable amount in nature is uranium, atomic number 92. (The atomic number refers to the number of protons in an atom’s nucleus.) Beyond that, scientists must create new elements in accelerators, usually by smashing a beam of light atoms into a target of heavy atoms. Every so often, the nuclei of the light and heavy atoms collide and fuse, and a new element is born. Slamming neon (element 10) into uranium, for example, yields nobelium (102).
But the odds of fusion (and survival) decrease markedly as atoms grow heavier because of increased repulsion between the positively charged nuclei, among other factors. Creating most elements in the superheavy realm (beyond 104) therefore requires special tricks. Oganessian developed one in the 1970s: cold fusion. Unrelated to the notorious nuclear power work of the 1980s, Oganessian’s cold fusion involves uniting beam and target atoms that are more similar in size than those in traditional elementmaking. And rather than smashing them together, “We bring two nuclei together so that it is a ‘soft touching,’” Oganessian says. Doing that is harder than it sounds because the beam and target nuclei are both positively charged and therefore repel each other. Incoming atoms need enough speed to overcome that repulsion, but not so much that they blow the resulting superheavy nucleus apart.
A team at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, perfected Oganessian’s technique and used it to create elements 107 through 112. But the method ran into limitations as the odds of fusion and survival dropped precipitously. Starting in 2003, a team at the RIKEN Institute in Wako, Japan, tried to use cold fusion to create element 113, firing zinc (element 30) onto bismuth (83). They got one atom the next year and another in 2005, which they celebrated in their control room with cheers, beers, and sake.
Then, the agony started. Needing one more atom to confirm the discovery, the RIKEN team reran the experiment in 2006 and 2007. None appeared. They tried again in 2008 and 2009. Nothing. Not until 2012—7 years later—did they detect another. “Honestly, we felt that we would be not lucky,” remembers RIKEN nuclear chemist Hiromitsu Haba. “Only God knows the statistics.” None of the atoms survived longer than 5 milliseconds before decaying.
Getting beyond 113 required a different approach, hot fusion, which Flerov scientists had developed in the late 1990s. Hot fusion uses higher beam energies and relies on a special isotope with a large excess of neutrons, calcium-48. (Neutrons stabilize a superheavy atom by diluting the repulsive force of protons, which would otherwise tear the nucleus apart.) Calcium-48 is expensive—it must be laboriously isolated from natural calcium sources—at $250,000 per gram. But the investment paid off. RIKEN sweated for 9 years to find three atoms of 113. Dubna snagged that many atoms of 114 within 6 months, a discovery Oganessian and colleagues celebrated in their control room with cheers, beers, and shots of spirits.
At that point, producing the next few superheavies was largely arithmetic. Calcium is element 20, and calcium plus americium (element 95) yielded element 115. Calcium plus curium (96) yielded element 116, and so on. By 2010, Dubna—in collaboration with scientists at Lawrence Livermore National Laboratory in California and Oak Ridge National Laboratory in Tennessee—had filled the periodic table’s seventh row.
After 118, however, things stalled again. Fusion requires several milligrams of the target element, and producing enough einsteinium (element 99) to make element 119 is impossible with today’s technology. Some researchers proposed replacing calcium-48 with titanium-50, which has two more protons, and then firing it at elements 97 and 98 to produce 119 and 120, respectively. But for technical reasons, the likelihood of fusion is just one-twentieth as high with titanium as with calcium. For most accelerators, that drops the odds of success into the realm of RIKEN’s experiments to create 113—God’s statistics all over again.
The SHEF was built to overcome those obstacles. In contrast to the grease monkey feel of the older Flerov accelerators, the SHEF is pristine: Bubble wrap still covers the door handles, and for now the floors are spotless.
Overall, the SHEF is a fusion of the brawny and the delicate. The beam originates in an ion source and accelerator that stands two stories high, bigger than some dachas in town. The ion source fires off 6 trillion atoms per second, 10 to 20 times as many as other elementmaking accelerators. After twisting through a few 90° turns—the most compact arrangement in a tight space—the beam plummets into a massive cyclotron, whose very presence here is remarkable. The cyclotron’s 1000-ton magnet was fabricated in 2014 in Kramatorsk, Ukraine, near the front line of the recent war with Russia, says Alexander Karpov, a Flerov physicist. The city endured heavy shelling and other military action then, and Karpov says lab personnel were nervous that the magnet would be damaged or destroyed.
After accelerating the beam to roughly one-tenth the speed of light, the cyclotron directs it toward the delicate part of the operation: micrometer-thin metallic foils with target atoms plated onto them. Those foils are mounted onto a disk roughly the size of a CD, which spins to keep cool. If it didn’t, the beam would fry a hole in it.
If fusion occurs, the resulting superheavy atom sails through the foil. Unfortunately, the foil is so thin that gobs of other particles slip through as well, producing a blizzard of extraneous noise. That’s when the separator comes into play. It consists of five magnets painted the same bright red as a fire truck and collectively weighing twice as much as one—64 tons. Despite the bulk, the magnets are aligned to within 0.01 millimeters, and their fields are precise enough to filter out lighter atoms, including nearly all beam atoms, swerving them into a device called the beam dump.
The separator, like the beam source, gives the SHEF an advantage. Earlier separators were tuned to superheavy atoms with a narrow range of speed, charge, and direction; those that deviated too much ended up in the beam dump. The new separator is more generous, giving a pass to two to three times as many superheavy atoms.
After slaloming through the separator, an atom arrives at a silicon-germanium detector, which records the atom’s position and time of arrival and then starts to monitor it. Superheavy atoms decay by emitting a series of alpha particles—bundles of two protons and two neutrons. Releasing an alpha changes the atom’s identity: element 118 becomes 116, which becomes 114, and so on.
That decay chain is what allows scientists to identify, retroactively, which element they’ve created. Each alpha particle in the chain flies off with a characteristic energy. So if the detector spots an alpha with the right energy—and, crucially, sees that it emerged from the same point on the detector where a superheavy atom just landed—it begins to watch closely for more alphas.
To aid that search, the detector automatically shuts off the cyclotron beam to reduce the amount of cruft flying around. The shutdown also triggers a loud beep in the SHEF’s control room, where a few probably bored scientists will be sitting. (On a recent visit to another control room here, two graduate students were watching a schlocky sci-fi monster flick.) The bell is a moment of excitement amid the monotony.
It’s also superfluous. Inside the detector, the atom will continue to shed alphas: In fact, several events in the decay chain will already have occurred before the scientists even register the sound. With superheavies, it’s hard come, easy go. Only later—when the scientists comb through the raw data and match every detected alpha particle to a specific element in the decay chain—can they reconstruct which element they initially created.
The stronger beam and more generous separator should, in theory, cancel out the lower odds of titanium-50 fusion. That gives the Dubna team hope that atoms of 119 or 120 will soon reveal themselves. A team at RIKEN is also searching for 119, albeit using a different and perhaps harder method (firing vanadium, element 23, onto curium). Between the two labs, scientists are confident that 119 and 120 will appear somewhere within about 5 years.
If you look backwards over several decades people have made roughly one new element maybe every 3 years—until now.
It’s the next 5 years that worry people. Creating elements heavier than 120 might be impossible with hot fusion. Detecting them will be equally hard: If the expected lifetimes drop too low, the atoms might not survive the 1-microsecond trip through the separator. They could decay midflight instead—ghost atoms that disappear without a trace.
Moving beyond 120, then, will probably require new approaches. “Multinucleon transfer reactions” would involve firing, say, uranium onto curium at relatively low speeds—another “soft touching.” Their nuclei wouldn’t fuse completely, but a chunk of one might break off and glom onto the other. Depending on the size of the chunk, scientists might even leap to much higher element numbers instead of inching along one atomic number at a time.
Such methods remain unproven, however. “Heavy-element scientists like to work one piece at a time,” says Jacklyn Gates, leader of the heavy-element group at Lawrence Berkeley National Laboratory in California. And much beyond 120, she says, “We don’t know enough to even know what to look for—what half-life to look for, what decay properties to look for.”
Given those difficulties, some scientists propose ditching accelerators. In one approach, low-power nuclear blasts would induce fusion reactions in target atoms. That isn’t as crazy as it sounds: Elements 99 and 100 were first identified in the fallout of atmospheric atomic bomb tests. Still, most scientists are skeptical of that approach given the obvious radiation hazards and the short lifetimes of superheavy atoms, which might expire before they could be sifted from the nuclear debris.
Other scientists suggest finding new elements the old-fashioned way: by hunting for them in nature. That was actually a popular pastime a few decades ago, as physicists scoured cosmic rays, meteorites, moon rocks, and even ancient shark teeth for superheavies. Nothing ever came of those projects. Nowadays, focus has shifted to supernova explosions and anomalous stars such as Przybylski’s star, whose spectrum shows signs of einsteinium, which is otherwise never found in nature. Perhaps the star’s hot, dense interior houses even heavier elements.
Still, there’s no guarantee superheavy elements exist in nature. And the long dry spell—no new elements have been created since 2010—worries some researchers.
“If you look backwards over several decades,” says Pekka Pyykkö, a theoretical chemist at the University of Helsinki, “people have made roughly one new element maybe every 3 years—until now.” Today’s barrenness could be the new normal.
Even if scientists can overcome the technical challenge of creating new elements, other questions remain: How many elements can exist, even hypothetically? How far could the periodic table go?
One prominent theory predicts an end at element 172. No one knows what will happen above that point, but for quantum mechanical reasons, an atom’s nucleus might start to gobble up electrons and fuse them with protons, producing neutrons as a by-product. That process would continue until the proton count dropped back to 172, providing a hard cap on the atomic number. (And if that sounds weird, well, that’s quantum mechanics.)
Other research suggests elements will run out long before 172. As nuclei get larger, the repulsive force between protons becomes overwhelming. By general consensus, a nucleus must survive for at least 10−14 seconds to count as a new element. Given how fragile elements in the 110s already are, heavier elements might struggle to hold on even that long. Some scientists predict that nuclei can overcome that problem by twisting into exotic shapes—hollow bubbles or even latticelike buckyballs. But other scientists doubt those shapes would be stable.
Which is a shame, because exciting things could happen in the 130s or 140s. In particular, the sine qua non of the periodic table—its periodicity—could break down completely.
In general, all elements within the same column of the table have similar chemical and physical properties. But that trend might not hold true forever. Scientists across the world have managed to probe the properties of single superheavy atoms by studying how they adhere to different materials. And the association between columns and chemical behavior already seems to be breaking down in the 110s.
Element 114, for instance, acts like a gas at room temperature, even though the element above it, lead, is about the most un–gas-like substance imaginable. Similarly, although element 118 falls into the noble gas column, theory predicts that it will readily attract electrons—something no other noble gas does. Those anomalies arise because of relativistic effects: The high, concentrated charge of a superheavy nucleus distorts the orbits of surrounding electrons, which affects how they behave and form bonds.
As Haba says, “The chemical properties of superheavy elements are very unique, and we cannot simply extrapolate.” And although 114 and 118 seem to depart only modestly from expectations, even heavier elements could have wildly unexpected properties because relativistic effects will only grow larger as elements gain weight. So where should anomalous elements go? In the column where their atomic numbers say they should go or in a column with elements of similar properties?
The answer depends on whom you ask. For some scientists, the table is primarily about underlying atomic structure, not chemical behavior. Deviations are therefore not allowed. Other researchers are more pragmatic. “The periodic table is more useful for telling me what the chemistry of an element is, so I would argue for changing it around,” Gates says.
Pyykkö has pushed the idea of anomalous elements to its extreme, calculating theoretical properties for all elements through 172 and arranging them into a futuristic table. The result is jarring: At one point, the sequence of atomic numbers jumps backward from 164 to 139 and 140 before skipping ahead to 169 (see table, left). The bizarro table now hangs on his office wall. “When I give talks,” he says, “I usually joke that this periodic table should be enough for the rest of this century.”
Beyond the divisions over the structure of the table, a deeper rift exists between people who think pursuing new elements is worthwhile and those who think it’s a waste of time and resources. Gates voices her skepticism: “For elements 119 or 120, with our current technology, you’re looking at years of beam time potentially for one atom—and what does that tell you?”
Still, she understands why some labs pursue new elements: “A new element is what makes people interested. … And it does help you get funding. I just don’t think it’s science that’s driving the experiments. It’s politics.” Indeed, RIKEN’s 9-year pursuit of element 113 resulted in a nice budget boost. And because 113 was the first element created in Asia, the scientists became folk heroes in Japan. Someone even published a manga comic book about their work.
Dubna scientists argue their work is not mere trophy hunting. Karpov—who owns four sports jackets and wears a different Russian-themed element lapel pin on each (dubnium, flerovium, moscovium, and oganesson)—says making new elements can verify theoretical predictions about their half-lives and other properties.
He and his colleagues will also try, during some experimental runs, to add neutrons to existing superheavy elements and produce longer-lived versions of them. Nazarewicz, skeptical of making new elements, sees the value in that. “I would like us to get more stable,” he says. Tinkering with existing elements might even allow scientists to reach the island of stability—a supposed region of longer-lived superheavy elements—and study those elements’ properties. If nothing else, the technologies used to make new elements can help produce radioisotopes for medicine and test how well satellite components withstand bombardment by particles.
Ultimately, though, the search for new elements is its own reward—l’art pour l’art. “There’s a majesty to increasing the number of protons,” Karpov says. “It’s natural to come to a limit” and try to push beyond. Plus, he says with a smile, his moscovium lapel pin gleaming, “sometimes it is good to say you did something first.”