It has teased researchers for almost a decade. But new evidence for the existence of super-heavy element 113 could see Japan claim its first spot on the periodic table ? that is, unless a team in Russia wins official approval for its latest results and bags the right to name the element.
Confirming the find is about more than monikers. Proving a viable method for producing element 113 could lead to even heavier finds, bringing researchers closer to the "island of stability", a predicted set of very heavy elements that would remain stable for decades if created.
The heaviest known naturally occurring element is uranium, with atomic number 92. The atomic number refers to the number of protons in an atom's nucleus. The number of neutrons in the nucleus can vary, leading to versions, or isotopes, with different atomic masses.
All elements with a higher atomic number than uranium must be produced synthetically by smashing atoms together to create larger nuclei.
Super-heavy elements are difficult to pin down because they are incredibly unstable and decay into elements with smaller nuclei in a matter of milliseconds. But by observing decays that emit alpha particles ? combinations of two protons and two neutrons ? researchers can work backwards up the chain to identify the starting atom.
Solid chain
This week a team led by Kosuke Morita of the RIKEN Nishina Center for Accelerator-based Science in Saitama, Japan, announced what they say is conclusive evidence for an isotope of element 113.
The findings have been submitted to a joint working party for the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), which rule on evidence for new elements.
Morita's team uses a particle accelerator to shoot high-speed zinc ions (atomic number 30) at a target of bismuth foil (atomic number 83).
The group had previously claimed detection of element 113 via this method in 2004 and 2005, saying they produced a chain of decays that included spontaneous fission of an isotope of element 105, dubnium-262. Fission meant that some steps in the decay chain could not be attributed to alpha-particle emissions, making some of the lighter elements harder to distinguish definitively. IUPAC rejected that claim as inconclusive.
In their latest effort, the team produced a heavy atom that decayed only by emitting alpha particles until it became a stable isotope of element 101, mendelevium-254.
"We are really confident to say our product has atomic number 113 and mass number 278," Morita says.
Tried and true
But Yuri Oganessian of the Joint Institute for Nuclear Research in Dubna, Russia, says the Japanese team isn't the first to make element 113. In 2003 his team produced an atom of element 115, which then decayed to 113 and lighter elements, he says.
For their work, the Russian team used a new technique that starts with a heavier target ? in this case, they fired calcium (atomic number 20) at americium (atomic number 95). But their initial result was ruled inclusive by IUPAC and IUPAP.
Since then the Dubna experiments have produced one atom of 115 per day, and they have made five different isotopes of 113, Oganessian says. What's more, the same method was used to create the recently accepted elements 114 and 116, so he thinks the claim for elements 113 and 115 should stand.
The older method employed by Morita may be widely accepted, but it becomes much more difficult to make new elements as you move down the periodic table, which is why it has taken them nine years of hard work, he adds.
"It seems to me that nobody will repeat this experiment," Oganessian says of the Japanese research. "I don't think anybody would really make this time commitment." But new techniques could smooth the way towards the island of stability.
Naming rights
If both claims are verified, deciding which method succeeded first determines which team will get to name element 113.
Until now only scientists working at US, German and Russian laboratories have been able to claim discovery and name new elements. In 1908, Japanese chemist Masataka Ogawa was one of many to report the discovery of element 43, which he named nipponium after Nippon, the Japanese word for Japan. It was later determined he had actually made rhenium, element 75, and element 43 was officially named technetium by another claimant.
Morita says it is too early to discuss potential names for element 113, but says he hopes it could be related to Asia or Japan. Oganessian, meanwhile, congratulates Morita's team on their work, but he says what really matters is continued study of the new element.
"One isotope doesn't change very much, it is just one more test. It does not change our whole understanding," he says.
Journal reference: Journal of the Physical Society of Japan, DOI: 10.1143/JPSJ.81.103201
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