NESTLED in thick pine forests north of Moscow, close to the Volga river, lies the town of Dubna. Not far from the centre is a leafy avenue of Soviet-era buildings. It is obvious when I visit that they have seen better days. The railway crossing on the approach is broken, its flashing lights constantly proclaiming the coming of a train that never passes. A few of the buildings have broken windows. In the street, there are liquid nitrogen containers with old baked bean cans acting as lids.
But there is one place within this complex where something groundbreaking is happening. In a vast concrete hangar, workers in hard hats are busy assembling one of the most powerful research machines in the world. Next to me as I look on is the only living person to have an element named after him. Yuri Oganessian, Mr Element 118, is gazing almost lovingly at the 4-metre-wide metal disc in the centre of the hangar.
This is one of the first components of a machine that will soon begin churning out chemical elements 鈥� but not ordinary ones. These elements will be superheavy, with atoms so huge that they stick around barely long enough to be sure they exist.
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By forging these exotic atoms in quantities sufficient to study properly for the first time, Oganessian and his machine should be able to answer some big questions about how our universe formed, and possibly give us a staggeringly powerful source of energy. He might even disprove some of the rules underpinning the periodic table itself.
The birth of the modern table traces back to another Russian city, St Petersburg. It was there that a scientific consultant named Dmitri Mendeleev helped cut through the chaos that was chemical science 150 years ago.
With Mendeleev鈥檚 table, the patterns of chemistry began to make more sense. The Russian organised the 63 known elements by atomic weight, which we now know is determined by the number of protons and neutrons in an atom鈥檚 nucleus. As he did this, he found that certain chemical properties were periodic, repeating every eight or so elements. Mendeleev arranged the table鈥檚 columns so that each contained elements with similar traits. The first group, for example, holds soft, fiercely reactive metals like lithium, sodium and potassium. The last group contains the noble gases, so called because they are almost completely inert.
We now know that these patterns in the way elements react are governed by the electrons that orbit their nuclei. Every time we move one place along the table, an element gains a positively charged proton compared with its predecessor, as well as a negatively charged electron to balance the charge. The electrons sit in a series of concentric shells, which are most stable when completely filled. The extent to which the different elements have their shells filled is what drives their reactivity 鈥� and all chemistry on Earth, from the signals of neurotransmitters to the synthesis of antibiotics.
鈥淓lements on the 鈥榠sland of stability鈥� could be amazing fuels for nuclear power plants鈥�
As time went on, chemists discovered more elements, filling some of the gaps Mendeleev had astutely left in the table. By the 1940s, we had created the first synthetic elements, such as technetium, which are too unstable to exist in any significant quantity on Earth.
The reason for this instability boils down to an eternal rivalry between two of nature鈥檚 fundamental forces. The strong force holds protons and neutrons together in the atomic nucleus, but the electromagnetic force makes protons repel each other because they have the same charge. So the more protons an element has, the more likely it is that electromagnetism will win out and make it unstable. The heaviest elements we have made only last a fraction of a second.
Nevertheless, we keep trying to create new elements by cramming more protons and neutrons into the atomic nucleus. For that, you need a particle accelerator. Work of this kind has been going on for years at that complex in Dubna, the Joint Institute for Nuclear Research (JINR), which was set up to rival the CERN particle physics laboratory near Geneva, Switzerland, during the cold war.
The jewel in the JINR鈥檚 crown is the Flerov laboratory, where an accelerator called a cyclotron flings positively charged ions 鈥� atoms with slightly too few electrons 鈥� around a spiral track using magnets. Once up to speed, the ions are fired down a track to collide with a target nucleus. Most collisions simply break the components to pieces, but on rare occasions they fuse to form a superheavy atom.
In the past few years, accelerators in Japan, Germany and Russia have made a spate of new superheavy elements in this way, all the way up to number 118. But we know almost nothing about them. The most advanced experiment so far involves shooting the newly formed atoms across an array of gold pins with a temperature gradient, looking at how hot the gold must be for them to stick. For anything more involved, you would need a larger sample of atoms.
Yet there are hints that superheavy elements don鈥檛 play by the same rules as the others. 鈥淲e assume that the chemical properties in a group change systematically in some way,鈥� says at the University of Liverpool, UK. But calculations suggest that several of the superheavy elements we have already created would behave like a noble gas, even though they don鈥檛 sit in that group. If so, he says, 鈥測ou have to ask yourself if the periodic table as we know it is still valid鈥�.
Magnets and Gunshots
The calculations are rooted in Albert Einstein鈥檚 theory of special relativity. One of its implications is that objects get heavier the faster they are travelling. This matters in the case of larger elements because their nuclei hold greater positive charge, meaning the electrons are whizzing around faster and so appear a little more massive. In turn, that extra mass means they orbit closer in than we would expect, altering the chemical properties of the atom.
That鈥檚 the theory. And the new machine being built in that concrete hangar at JINR is where we should soon find out whether it is right. 鈥淚s 118 a noble gas or not? If not, it means that this is the end of periodicity,鈥� says Oganessian.
When I visited in 2016, the Flerov lab was still building its new cyclotron, known as the Superheavy Elements Factory or SHEF. It wasn鈥檛 easy, because this machine relies on a more intense ion beam, and that meant installing a much bigger magnet.
There are only so many places that can make a 2000-tonne electromagnet. The Russian scientists chose a factory in eastern Ukraine. But just as the magnet was due to ship in 2014, war broke out. Staff from the JINR say that when they called the factory to check in, they could hear gunshots in the background. Fortunately, the magnet was winched safely onto a train 鈥� no road truck would be sturdy enough to carry it 鈥� and some days later it arrived, passing the same broken railway crossing I had seen on my way in.
Now the SHEF is undergoing final tests, ready to begin running at full capacity this spring. The next best cyclotrons can produce one superheavy atom a week. The element factory should be 100 times more productive, so soon we should have enough superheavy atoms to start trying new experiments.
鈥淵ou can consider things like putting them in a trap, measuring their mass. You can do chemistry experiments,鈥� says at Lawrence Livermore National Laboratory in California, who contributed to the discovery of several superheavy elements. The atoms could, for example, be sent into a chamber containing a reactive element such as chlorine to see if they bond with it. If not, that is a hint that the atoms are unreactive like a noble gas.
There may also be new hidden gems to discover among the superheavies. This is because elements come in different forms called isotopes, each with a different number of neutrons. Elements are defined by the number of protons in their nucleus: if there is one, it is hydrogen, if there are two, that is helium, and so on. But isotopes of a helium nucleus can contain either one, two or zero neutrons.
It is a similar deal at the heavy end of the periodic table. Take element 114, flerovium, which, you guessed it, was first made at the Flerov lab. It has a variety of isotopes, but this time there is a chance that some of them may be stable for long periods of time.
It turns out that particles in the nucleus come in shells just like electrons do. In 1963, physicists Maria Goeppert Mayer, Hans Jensen and Eugene Wigner won the Nobel prize in physics for suggesting that protons and neutrons in a nucleus can add up to 鈥渕agic numbers鈥�. These correspond to when the shells are full, whereupon the nucleus would be highly stable. According to this theory, there should be pockets of superheavy elements that are incredibly stable.
Finding this long-fabled 鈥渋sland of stability鈥� could be incredibly useful. Any superheavies in it could last for thousands of years and would hold incredible amounts of energy because of their huge size. They would be an amazing fuel for nuclear power plants.
The SHEF is our best shot at getting to the edge of island of stability. This is where flerovium comes in. It has 114 protons, which is a magic number. And one of its possible isotopes has 184 neutrons, which is also a magic number. If we could make this doubly magic isotope, it could be stable for days 鈥� nothing compared with the heart of the island, but still impressive.
When researchers make flerovium in a cyclotron, each of the fusing nuclei typically ends up losing three or four neutrons as part of the way the impact energy is dissipated. That leaves an atom with up to eight fewer neutrons than the doubly magic isotope.
At the SHEF, researchers can afford to set up collisions at lower energies that would lose fewer neutrons. With lower energies there will also be less chance of the nuclei merging, but there will be plenty of collisions to generate enough atoms to study. 鈥淚f you have 100 times more production, you can put that into sensitivity, so making something that is 100 times harder to produce,鈥� says Herzberg. If only one or two neutrons were lost in the collisions, we would produce a flerovium isotope that would hang around for perhaps a few hours. We would be on the shores of the island.
Even if the SHEF doesn鈥檛 pull that off, it offers plenty of interest, says physicist at the University of Manchester, UK. 鈥淚t鈥檚 going to give us understanding of other areas of physics, such as supernovae,鈥� he says. We know that the superheavy elements are created in supernovae and in neutron star collisions, which are complex cosmic events that even our best computers cannot model. But with more information about what these elements look like, we can build a better picture of how they might act.
Supernovae may be light years away from the buildings nestled among the birch trees of Dubna. But this sleepy town might soon get us closer to them than ever before.
Check out the rest of our special聽on聽the 150th anniversary of the periodic table:聽
- Find out聽why the most beautiful table in science is worth celebrating
- 顿颈蝉肠辞惫别谤听the story of the birth of the table
- 尝别补谤苍听
- Try our special crossword
- Discover the favourite elements of some top scientists聽and share your own
- How well do you know the periodic table?聽Try our quiz
