Berkeley Lab scientists used beams of titanium to create atoms of element 116. Not only does this represent a new way to make ultra-rare elements, but it's also a proof of concept that they might soon be able to make the yet-to-be-discovered element 120, which might be stable.
The periodic table arranges elements according to their atomic number, which is the number of protons in the nucleus of each element's atom. While the first 94 elements on the list are all found in nature, elements heavier than them can only be created in a laboratory by fusing existing elements together.
On paper, this sounds relatively simple: If you want an element with a specific atomic number, just fuse two other elements with the same total number of protons together. For example, to create the element ogane, which has 118 protons, scientists typically shoot a beam of calcium (which has 20 protons) at a target made of californium (which has 98 protons).
This is how the superheavy elements 112 to 118 were originally synthesized. It is expected that there will be more elements beyond the edges of the periodic table, but unfortunately, californium is the heaviest element that can be used as a target - the following elements are all too unstable.
So if you can't change the target, then change the projectile. That's what the Berkeley Lab team has now done, by boosting the beam from calcium to titanium, which has 22 protons, getting an extra two protons. However, doing so is not as easy as it sounds.
First, the process requires titanium-50, a rare isotope that accounts for only about 5% of the total naturally occurring titanium on Earth. The titanium-50 is then heated in a specialized oven, raising the temperature to nearly 3000°F (1649°C), causing the titanium to evaporate. An ion source creates a charged titanium plasma, which is then manipulated into a beam that is fired at a target.
This was the first time a titanium beam had been used in a similar experiment, so to test whether it worked, the team fired it at a target made of plutonium, which has 94 protons. This resulted in element 116, "Fish". Sure enough, the team detected this elusive element, albeit very rarely: only two atoms were produced during the 22 days of experiments.
With this proof of concept in hand, the team now plans to use titanium beams to search for the hypothetical element 120. This can be achieved by firing titanium at a californium target - although this is expected to be more rare.
"We think it will take about 10 times as long to make 120 as it does 116," said Reiner Kruecken, director of Berkeley Lab's Nuclear Sciences Division. "It won't be easy, but it now appears to be feasible."
It is predicted that if element 120 is discovered, it will be an alkaline earth metal (or "Unbinilium") and will join the also undiscovered element 119 in the currently empty eighth row of the periodic table.
But the most exciting thing is that Element 120 is likely to be located on an "island of stability." Superheavy elements typically have short half-lives, meaning they decay within milliseconds, making them difficult to study and basically impossible to use for any practical purpose. However, it is predicted that certain isotopes of these elements may have just the right number of neutrons to balance out the entire process, making it stable for minutes or even days. If so, Element 120 could become the most useful new element created in quite some time.
Researchers could begin experiments as early as 2025, though it could still be several years before any atoms of element 120 are produced.
The research has been submitted to the journal Physical Review Letters.