Japanese researchers have staked their claim to discovering element 113, based on results of massive ion bombardment experiments published today.
The team, led by Kosuke Morita at the RIKEN Nishina Centre for Accelerator-based Science in Wako, is hoping that its experiments will lead to the first naming of a new element by Japanese researchers.
The team made atoms of element 113 by smashing a beam of 70Zn ions (Z = 30) into a target made of 209Bi (Z = 83). After thousands of hours of bombardment, they had made enough atoms of element 113 and compiled enough data about its decay chain to make a claim about the identity of the new element.
Because most superheavy elements are unstable and decay after only a fraction of a second, their identity is normally verified by looking at the type and energy of the radiation they emit as they decay, and the nuclides that are produced as they do so. To be sure of the identity of a new element, it has to decay by a series of steps into well-known nuclides.
For example, confirmation of the identities of the recently ratified elements 114 (flerovium) and 116 (livermorium) was helped by the earlier recognition of element 112 (copernicium). This is because both elements 114 and 116 decay by emitting alpha particles (two protons and two neutrons) so livermorium decays first to flerovium, then to copernicium, then onwards by another alpha decay to darmstadtium and so on. That meant that until copernicium was officially recognised, the claims for flerovium and livermorium had a missing link in their decay chains.
In 2004-5, the Japanese team completed experiments in which atoms of element 113 decayed to element 111 (which was only officially ratified by the International Union of Pure and Applied Chemistry, Iupac, at the end of 2004 and is now known as roentgenium), followed by three more alpha decays to dubnium-262. Unfortunately, the 232Db atoms underwent fission, breaking apart into much smaller nuclei in the same process that occurs in uranium-235 when it is powering nuclear reactors or atomic bombs.
The Iupac–Iupap joint working party considering claims for discovery of elements up to atomic number 118 produced its latest findings last year. Because the daughter nuclides of the 262Db fission process were not well enough known, the report concluded that there was not yet enough evidence to support the Japanese team’s claim. However, the working party also concluded that no other team had yet provided sufficient evidence to satisfactorily claim having made the element either.
So the door is still open. In this latest paper, the Japanese team has managed to observe the 262Db atoms undergoing alpha decay instead of fission. This produces lawrencium-258, followed by another alpha decay to mendelevium-254, and this decay chain is well known. The Japanese team says that this provides unambiguous proof that they have made element 113.
However, before the team can even think about naming the new element, the results must be ratified by the Iupac–Iupap working party. Unfortunately, the latest round of evidence submissions for claims relating to elements 113, 115, 117 and heavier closed at the end of May, so it will be some time until this claim is even considered by the panel, unless the rules can be bent a little bit…
It looks to me as if the Japanese team may have to hang on a little longer before they can attempt to break the dominance of the Russian, German and American teams that have been responsible for naming all the trans-uranic elements so far.
Phillip Broadwith
