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Physicists add another element to table

It's superheavy A new superheavy element looks set to be added to the periodic table with the help of Australian researchers.

An international team of physicists and chemists, led by researchers at Germany's GSI laboratory, have successfully created atoms of element 117.

The work, published today in Physics Review Letters, corroborates the original discovery of the superheavy element by a joint US-Russian team in 2010.

However, the international committee that defines the periodic table, IUPAC, does not accept the creation of a new element until there is independent corroboration.

"We've managed to find four atoms of the same element 117, that hopefully will be sufficient to allow it to be officially recognised and then named," says co-author Professor David Hinde, at the Australian National University.

He says the creation of element 117 "is at the absolute boundary of what is possible right now".

"That's why it's a triumph to create and identify even a few of these atoms."

The periodic table consists of 92 naturally occurring elements ranging in weight from atomic number 1, hydrogen, through to uranium, number 92.

Each element is defined by the number of protons in its nucleus — hydrogen has one proton, while the new element — currently known as ununseptium — has 117 protons.

Colliding nuclei

Elements beyond atomic number 92 have been artificially created by fusing the nuclei of smaller atoms that combine to give the right number of protons.

Hinde says this is where the Australian team is playing a critical role for future attempts to form even heavier elements.

Using ANU's Heavy Ion Accelerator Facility, of which Hinde is director, the team is able to identify the best choice of nuclei to collide.

"The properties of different nuclei are very different and that has a big effect on the probability of whether they will stick together," says Hinde.

However, even after identifying potential nuclei to use in the experiment, the chances of forming a single atom of element 117 are very low.

Hinde points out the researchers were able to identify just four atoms of element 117, which last for just a tenth of a second.

Yet to create those four atoms, he says, the team led by researchers at Germany's GSI laboratory, had to fire more than ten billion billion rare calcium-48 nuclei — made up of 20 protons and 28 neutrons — at a target made of the even-rarer isotope, berkelium-249.

"That is a huge, huge number of collisions to get the result that is needed," says Hinde.

Understanding the atom

The main benefit of the creation of these superheavy elements is to better understand nuclei.

"If we push beyond what is already known we can refine models and determine what are the proper physical descriptions of nuclei and the chemical properties of elements," says Hinde.

With the publication of their work, Hinde says the team has its sights on elements 119 and 120.

"It would be good to confirm element 118 [already created by the Russian team], but the next stars on the horizon are 119 and 120," he says.

Hinde says it is expected these will be particularly difficult to create as calcium-48 will no longer work as a projectile.

"We then have to use heavier projectiles and it is hard to know which is the best. Our experiments here at ANU will help to clarify this problem," he adds.