How New Elements Are Made: Inside the Hunt for Element 119

How scientists create superheavy elements by smashing nuclei together, detect a handful of atoms from their decay, name them, and hunt for elements 119 and 120.

The periodic table on this site ends at element 118, oganesson, not because chemists have run out of ideas but because making anything heavier is one of the hardest experiments in science. Every element beyond number 92, uranium, has to be manufactured, and the heaviest exist for less than a second.

Why the heaviest elements do not survive on Earth

The nucleus of an atom is a crowded place. Protons all carry a positive charge and push each other apart, while a much shorter-range force, the strong nuclear force, glues protons and neutrons together. In light and medium-sized nuclei the glue wins comfortably. As you add more protons the electrical repulsion grows and the nucleus becomes less and less stable.

Beyond a certain size no combination of protons and neutrons lasts indefinitely. Uranium and thorium are heavy but decay so slowly that plenty remains from the formation of the Earth. Elements a little beyond them decay in years or centuries, so any that formed alongside the Earth vanished long ago. The superheavy elements at the far end of the table decay in seconds, milliseconds or less. If they ever existed naturally, they were gone almost immediately.

This is why the elements from 93 onwards are described as synthetic. Apart from traces of neptunium and plutonium in uranium ores, they have only ever been seen because a laboratory made them on purpose.

Fusing two nuclei together

The recipe sounds simple: take two lighter nuclei whose proton counts add up to the number you want, and make them stick together. In practice both nuclei are positively charged and repel one another fiercely, so the lighter nucleus has to be fired at the heavier one at a substantial fraction of the speed of light.

That is the job of a particle accelerator. A thin target foil containing a heavy element, such as americium, curium, berkelium or californium, is bombarded with a beam of lighter ions for weeks or months at a time. The beam of choice for many of the recent discoveries was calcium-48, an isotope with 20 protons and 28 neutrons.

Why that isotope? Heavy nuclei need a generous ratio of neutrons to protons to hold together, and a fused nucleus that is too neutron-poor flies apart at once. Calcium-48 is unusually neutron-rich for a light element, so it delivers extra neutrons along with its 20 protons. It makes up only a tiny fraction of natural calcium and must be separated at great expense, and then most of the beam passes straight through the target.

Even when two nuclei do touch, the hot compound nucleus usually splits apart within an instant. Only a minute fraction cools down by shedding a few neutrons and survives. A successful experiment may produce a single atom of the new element in a week of continuous running.

Detecting a handful of atoms

You cannot put one atom on a balance. Instead, researchers rely on the fact that a superheavy nucleus announces its identity by the way it dies.

Behind the target sits a separator, a set of magnets and electric fields tuned to sweep away the unreacted beam and the debris while guiding any heavy products onto a detector. The detector is a silicon chip that records exactly where and when a particle arrives and how much energy it carries.

A freshly made superheavy atom typically decays by emitting an alpha particle, a bundle of two protons and two neutrons, becoming the element two places lower on the table, which decays in turn, and so on down a chain. Each step releases a characteristic energy after a characteristic delay. An arrival followed by alpha particles at the same spot with the right energies and time gaps is the fingerprint of a specific chain, and the top of the chain tells you what was made.

The strongest evidence comes when a chain ends at an isotope that is already well known, because following the steps back up then pins down the new nucleus. Discovery claims are judged by a joint working party of the International Union of Pure and Applied Chemistry (IUPAC) and its physics counterpart, which examines the chains and whether the results have been reproduced.

The laboratories

Only a few places in the world have the accelerators, targets and patience needed for this work.

• Dubna, Russia. The Joint Institute for Nuclear Research, north of Moscow, has been the most prolific discoverer of superheavy elements in recent decades, often in collaboration with American laboratories that supplied rare target materials. Dubnium (105) is named after the town.
• GSI Darmstadt, Germany. The GSI Helmholtz Centre for Heavy Ion Research discovered elements 107 to 112, including bohrium, hassium, meitnerium, darmstadtium, roentgenium and copernicium. Darmstadtium and hassium (from Hessen, the surrounding state) both record the location.
• RIKEN, Japan. The RIKEN Nishina Center near Tokyo was credited with element 113, nihonium, the first element discovered in Asia, after years of colliding zinc with bismuth to obtain a small number of confirmed events.
• Berkeley, USA. The Lawrence Berkeley National Laboratory in California was the birthplace of many earlier synthetic elements, from neptunium and plutonium through to seaborgium. Berkelium, californium, americium and lawrencium all honour this history.

How new elements get their names

A new element is first known by a placeholder name built from Latin and Greek roots; element 119 is currently ununennium and element 120 is unbinilium. Once IUPAC accepts a discovery, the discoverers are invited to propose a permanent name.

The rules are clear. A name may honour a mythological concept or character, a mineral or similar substance, a place or region, a property of the element, or a scientist. It must end in "-ium" for most elements, "-ine" for a halogen in group 17 and "-on" for a noble gas in group 18. The proposal is published for public comment before it is confirmed.

The most recent batch of names was approved in 2016 and completed the seventh row of the table:

• Nihonium (Nh, 113), from Nihon, a Japanese name for Japan.
• Moscovium (Mc, 115), after the Moscow region where Dubna is located.
• Tennessine (Ts, 117), after the state of Tennessee, home to Oak Ridge and other contributing institutions, with the halogen ending.
• Oganesson (Og, 118), after Yuri Oganessian, a leading figure in superheavy element research, with the noble gas ending. He is one of only two people to have an element named after them during their lifetime.

The island of stability and the hunt for 119 and 120

An island in a sea of instability

If heavier nuclei are always less stable, why bother pushing further? The answer is a long-standing prediction called the island of stability.

Just as electrons fill shells, protons and neutrons inside the nucleus also occupy energy levels. Certain numbers of protons or neutrons complete a nuclear shell and make the nucleus noticeably tougher. Theorists have long predicted that a closed shell should exist somewhere around 114 protons and 184 neutrons. Nuclei near that point might survive for minutes, days or even longer, compared with the milliseconds seen for their neighbours.

There is encouraging evidence: the heaviest elements made so far live longer when they carry more neutrons, exactly as the island picture predicts. But even with calcium-48 beams and the most neutron-rich targets available, the products fall well short of 184 neutrons. Researchers are exploring the shoreline while the island itself remains out of reach.

Pushing past 118

Calcium-48 was the workhorse beam up to element 118 because californium, with 98 protons, was the heaviest practical target. Going further requires a heavier beam such as titanium, chromium or vanadium, which makes fusion even less likely, so experiments must run for longer with more intense beams and better separators.

Several groups are actively trying. RIKEN has been running a long campaign aimed at element 119 using a vanadium beam on a curium target. Dubna's Superheavy Element Factory has been commissioned with element 120 as one of its goals, and laboratories in the United States have demonstrated that titanium beams can produce known superheavy elements as a stepping stone towards heavier targets. At the time of writing, no discovery of element 119 or 120 has been officially confirmed, though claims may appear at any time and will then face the usual scrutiny.

Whoever succeeds will open the eighth row of the periodic table and some genuinely open questions. Will these elements still fit the familiar column patterns, or will relativistic effects on their electrons scramble the chemistry? Even oganesson, notionally a noble gas, is predicted to behave quite differently from helium and argon.

You can explore all 118 confirmed elements, including the seven synthetic ones that fill out the final row, on the interactive periodic table. The details panel for oganesson is a good place to see how little is known about the newest arrivals.

Key takeaways

• Elements beyond uranium decay too quickly to have survived since the Earth formed, so they must be manufactured in laboratories.
• New elements are made by accelerating a light nucleus, often neutron-rich calcium-48, into a heavy target so that the two fuse.
• Successful fusion is extremely rare, and new atoms are identified by their characteristic chains of alpha decays rather than by direct observation.
• Dubna, GSI Darmstadt, RIKEN and Berkeley have discovered most of the synthetic elements; IUPAC rules on discovery claims and names.
• The 2016 names nihonium, moscovium, tennessine and oganesson completed the seventh row of the table.
• Theory predicts an island of stability near 184 neutrons, and several laboratories are currently attempting elements 119 and 120.