Researchers have demonstrated a new way to make superheavy elements, offering a method to create element 120 — which would be the heaviest element ever made.

Scientists at the Lawrence Berkeley National Laboratory in Berkeley, California, announced today that they have for the first time used a beam of titanium to make a known superheavy element, livermorium — element 116. After upgrading the lab’s equipment, the team plans to use similar techniques to try to produce element 120. The heaviest element that has been made so far is oganesson, element 118, which was first synthesized in 2002.

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The research is “truly groundbreaking”, says Hiromitsu Haba, who leads the Superheavy Element Research Group at RIKEN Nishima Center for Accelerator-based Science in Saitama, Japan. “The search for the superheavy elements beyond 118, oganesson, is proving to be a great challenge,” he says. Data from the experiment will “greatly improve the accuracy of existing theoretical calculations, and will greatly advance mankind towards the discovery of elements 119 and 120”.

Haba is part of a team at RIKEN aiming to produce element 119. Superheavy elements are extremely challenging to make, requiring hard-to-produce starting materials and long-running experiments, so some nuclear-physics groups focus on one rather than another.

The Berkeley team presented its results at the Nuclear Structure 2024 conference in Lemont, Illinois, and describe them in a preprint posted to the arXiv¹. The team says it has submitted the work to a journal.

Nuclear limits

Superheavy elements don’t occur naturally on Earth, but scientists think that they might appear in stars. They are highly radioactive, break down quickly through nuclear fission and have little prospect of direct practical applications. But by making new elements, scientists deepen understanding of how the Universe works, and fill in theoretical models of how the atomic nucleus behaves and of its limits — such as how many protons and neutrons it can hold.

Jacklyn Gates, leader of the Heavy Element Group at the Berkeley lab, says that chemists are particularly excited about the next set of elements, because they will fall in a new row of the periodic table. Elements 119 and 120 will be the first documented from the eighth ‘period’. In this row, scientists expect to find atoms with so-far unseen electron configurations, or orbitals. Chemists are excited about the potential to observe g orbitals, says Gates, which will provide “an entirely new set of orbitals to play around with and explore the chemistry of”.

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To make new elements, researchers use particle accelerators to collide beams of ions with atoms in solid targets, hoping to induce nuclear reactions that will fuse their nuclei to produce elements with ever greater numbers of protons and neutrons. But existing starting materials are running out of steam. The most recent set of superheavy elements to be discovered, numbers 114 to 118, were all produced by bombarding targets made of actinides (elements from the seventh period) with beams of calcium-48, which has 20 protons and 28 neutrons. This isotope of calcium is particularly stable, which makes it ideal for encouraging the necessary nuclear-fusion reactions.

Yet calcium can take scientists only so far into the outer reaches of the periodic table. Getting to element 120 with a calcium beam would require a target that can provide at least an extra 100 protons. But making targets from such heavy elements, which are all rare and radioactive, is extremely challenging. The heaviest element scientists can produce in sufficient quantities to turn into targets is californium, which has just 98 protons. So the only way forward is to work with heavier beams.

Heavy is the beam

Scientists have tried to make superheavy elements with beams heavier than calcium-48, including isotopes of titanium and chromium. “But for some reason, they didn’t see anything,” says Witek Nazarewicz, chief scientist of the Facility for Rare Isotope Beams at Michigan State University in East Lansing.

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To establish that titanium-50 beams could be used to make superheavy elements, Gates’s team made livermorium-290, an isotope that had previously been produced only with calcium beams. “The titanium beam is really hard to make,” says Gates. Titanium’s melting point is almost 1,700 ºC, more than twice calcium’s. “To make a titanium beam, you have to heat it enough to get ions to evaporate off, and you’re putting this a couple inches from things that have to be cooled to liquid-helium temperatures,” she says. The team used the Berkeley lab’s 88-Inch Cyclotron facility to accelerate the titanium beam and fire it at a target made of plutonium.

Yuri Oganessian, who leads the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, has been involved in the synthesis of several new elements and is the namesake of oganesson. He says that data such as those presented by Gates are “an obligatory step on the way to new elements”.

Oganessian says that his lab has been performing experiments with titanium and chromium beams to study superheavy elements and explore new ways to make them. “The synthesis of element 120 is not an end in itself in our research programme,” he says. In October 2023, the JINR said in a press release that its scientists had produced a previously unseen isotope of livermorium using a beam of chromium and a uranium target, showing that a chromium beam would work to make element 120. Oganessian says that the team is gathering more data before submitting the findings to a journal.

Theoretical improvements

Data from such experiments will improve theoretical models, says Nazarewicz. Part of the challenge is that theory can’t provide much guidance about this region of the periodic table. Depending on the energy of the ion beam used to bombard the target, the probability of producing a given superheavy isotope can vary widely.

“If you do not run at the correct energy, after a certain time, you will see nothing,” says Nazarewicz. Experiments run at the optimal energy are more likely to make rare nuclei. But predictions of the best energy for producing element 120 diverge widely. “We don’t know which of these models are correct,” says Nazarewicz. The Berkeley team “got one point on this diagram — now we’re not totally blind”, he says. (Nazarewicz declined to comment on the JINR work before publication.)

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Gates says that her team’s next steps are to repeat the synthesis of livermorium with the titanium set-up to narrow down the best experimental parameters. Then, the researchers plan to collaborate with scientists at Oak Ridge National Laboratory in Tennessee to generate a californium target to use in experiments with the aim of making element 120. The Berkeley facility will have to be upgraded to make sure its staff and equipment are adequately protected from this radioactive material.

Gates estimates that, once the experiments begin, the researchers will need 100–200 days of run time bombarding californium with titanium before they produce element 120. In practical terms, that will take two to three years.

“Now, we can only say that the synthesis of element 120 is not hopeless. But at what price?” says Oganessian. He estimates that it will take about 6 years of continuous run time to produce element 120. He adds that more preparatory experiments such as those being done at his and the Berkeley lab will help scientists learn how to reduce this time — “unless a miracle happens, which can never be completely ruled out in science”.