Physicists may now have a way to make element 120 – the heaviest ever

The third-heaviest element in the universe has been made in a way that offers a route for synthesising the elusive element 120, which would be the heaviest element in the periodic table.

“We were very shocked, very surprised, very relieved that we didn’t make any bad choices in setting up the instrumentation,” says Jacklyn Gates at Lawrence Berkeley National Laboratory (LBNL) in California.

She and her colleagues created the element livermorium by smashing a beam of charged titanium atoms into a piece of plutonium. Titanium has never been used in such an experiment because it is tricky to turn it into a well-controlled beam and it takes millions of trillions of collisions to produce very few new atoms. Yet, physicists think a titanium beam will be crucial for creating the hypothetical element 120, also known as unbinilium, which would have 120 protons in its nucleus.

The researchers started with rare isotopes of titanium, which they vaporised in a special oven at 1650°C (around 3000°F). Next, they used microwaves to turn the hot titanium vapour into a charged beam, which could then be fed into a particle accelerator. When the beam reached roughly 10 per cent of the speed of light and collided with the plutonium target, the resulting debris hit a detector that revealed signatures of exactly two atoms of livermorium.

Each atom rapidly decayed into other elements, as was expected – the stability of atomic nuclei decreases as the mass of an atom increases. But the measurement was so precise that there is only about a one in a trillion chance that the finding was a statistical fluke, says Gates. The researchers presented their findings on 23 July at the Nuclear Structure 2024 conference at Argonne National Laboratory in Illinois.

Michael Thoennessen at Michigan State University says this experiment strengthens the case for the feasibility of creating element 120. “You have to do the groundwork and feel your way up to it. In this sense, this is a really important and necessary experiment,” he says.

Thoennessen says that creating unbinilium would have deep implications for our understanding of the strong force, which determines when heavy elements are stable or not. Studying unbinilium could also help us understand how exotic elements may have formed in the early universe.

The heaviest human-made element so far – element 118, also known as oganesson – has two more protons than livermorium and was first synthesised in 2002. In the intervening years, researchers have struggled to make atoms any heavier because that requires smashing together already very heavy elements, which tend to be unstable themselves. “This is really, really difficult business,” says Thoennessen.

But the new experiment makes the LBNL researchers optimistic. They plan to start the experiment aimed at creating element 120 in 2025, once they have replaced the plutonium target with the heavier element californium.

“I think we’re a lot closer to knowing what we have to do,” says Gates. “And having the chance to put a new element on the periodic table [is exciting]. So few people have that opportunity.”