Lurking at the fringes of the periodic table, superheavy element 115 has been a favoured material in UFO conspiracy theories and video games. Now we may have evidence that it actually exists.

A group led by Dirk Rudolph of Lund University in Sweden reports the creation of 30 atoms of element 115, informally called ununpentium. Their sightings back up previous reports from a group in Russia, although the results must be reviewed by an international chemistry committee before they are deemed official.

Superheavy elements are more than scientific curiosities. Seeking them allows us to probe the boundaries of matter and possibly find the “island of stability“, a group of heavy elements that scientists predict will be stable for decades – if they could only be produced. If confirmed, the recent sighting would include the first observations of X-ray and gamma ray emissions from the decay of element 115, which could illuminate theories about the structure of superheavy nuclei in general.

Off the island

Each element on the periodic table has an atomic number, which corresponds to the number of protons in its nucleus. Most elements heavier than uranium (atomic number 92) are highly unstable and decay within seconds, making it hard to track them down in nature. These elements must be synthesised in the laboratory by smashing atoms together to create larger nuclei. Researchers can then sift through the decay products to tell if the collision briefly forged the desired heavyweight.


Element 115 was originally theorised to be inside the island of stability, which made it a popular candidate as an alien power source among UFO enthusiasts and science fiction writers. The superheavy element was featured as spaceship fuel in the X-COM video game series, and a meteorite containing element 115 was one of the main artefacts sought by Lara Croft in the game Tomb Raider III.

But when Yuri Oganessian of the Joint Institute for Nuclear Research in Dubna, Russia, and colleagues first created a single atom of element 115 in 2003, it turned out to be highly unstable.

From Russia with snub

That team fired atoms of calcium (atomic number 20) at a sheet of americium (atomic number 95) to create element 115, which decayed almost immediately to element 113, which itself decayed into still lighter elements. By examining these chains of decays, the team was able to infer that element 115 had been present.

But the arbiter of new elements, the International Union of Pure and Applied Chemistry (IUPAC), ruled the Russian team’s results inconclusive. Element 115 can decay via multiple pathways, some of which are tough to trace, and the team only recorded a handful of definitive sightings. Rudolph’s group also fired calcium at americium, but they claim to have created a record 30 atoms of element 115.

“Now with multiple detections you gain a lot of confidence because you see the same numbers over and over again,” says Paul Karol, chairman of the IUPAC committee responsible for confirming elements with atomic numbers greater than 113.

X-ray fingerprint

As well as examining decay products, Rudolph and his colleagues also observed X-ray and gamma-ray emissions from the unstable atoms. As they decay, each element gives off X-rays with a characteristic energy, depending on the kind of attraction between the atom’s electrons and its nucleus. That makes X-rays a good way to uniquely identify new elements, says Karol. “That’s different for every single element – it’s a fingerprint,” he says. “It’s a very powerful measurement.” But because the IUPAC committee is still reviewing the data, Karol can’t say yet whether the new measurement counts as a confirmation.

And the gamma-ray emissions can eventually help reveal properties of the element, including its spin and energy levels – the characteristic values of energy each atom can have when it is excited. Oganessian say that would be even better than having his results confirmed, because the theories describing the internal structures of superheavy elements are still on shaky ground.

“I believe that when, as a result of an experiment, we will register not 30, but 300 decay chains, these states will be definitively identified,” says Oganessian. “And when we have 3000 events, we, I hope, will be able to understand the nuclei structure of superheavy elements.”

Journal reference: Physical Review Letters, in press