The periodic table has been extended, with the announcement of the confirmation of the yet to be named element 117.
In 2010 a US Russian collaboration announced they had produced atoms of an element with 117 protons, filling a gap that appeared when 118 was made four years earlier. However International Union of Pure and Applied Chemistry (IUPAC) insists on corroboration by two independent teams before it allows new elements to be added to the Periodic Table, although a temporary name of Ununseptium is in use until confirmation has been made. It has taken four years, but this appears to have finally arrived.
“Making element 117 is at the absolute boundary of what is possible right now,” says Professor David Hinde of the Australian National University, one of the authors of a paper published today in Physics Review Letters “That’s why it’s a triumph to create and identify even a few of these atoms.”
Hinde was part of a team at the GSI laboratory in Germany who fused calcium 48 and berkelium 249. This is not easy, because berkelium 249 is both hard to produce in substantial quantities and has a half life of 320 days. Less than half of any amount produced will still be around a year after it was made, which means transportation and purification can't wait. The resulting product, like all atoms heavier than lead, was unstable. By watching the alpha particles emitted the team concluded that these were the product of two decay chains, both originating with 294117, that is an atom with 117 protons and 177 neutrons. One of the chains included the isotopes 270Db and266Lr, the latter adding four neutrons to the previous highest isotope of lawrencium.
In general large atoms have shorter half lives, that is decay more quickly through radiation, as their masses become greater. However, what are know as islands of stability exist, and the authors believe the one hour half life of 270Db “marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an “island of stability.'”
The manufacturing process was hardly efficient. More than 1019 atoms of 48Ca, not a common isotope in its own right, were fired at the berkelium to produce just four atoms of 117. Nevertheless, Hinde says, “On the basis of this paper it is likely that element 117 will be accepted.”
Element 117 is the most recent of six elements first announced by the Joint Institute for Nuclear Research in Russia. Of these 113, 115 and 118 remain unconfirmed, although claims have been made for the first two.
Such a small sample does not allow us to learn much about the chemistry of element 117. Ununseptium's position on the periodic table places it under the halogen gases such as fluorine and chlorine, but the strong capacity to capture electrons that makes these so reactive weakens as you go down the table, and in fact it is thought if one could ever produce enough to observe chemical interactions it would be more likely to lose electrons than gain them .
With a dozen new discoveries since he wrote The Elements, maybe it is time for Tom Lehrer to come out of retirement to add more lines to his song. Well we can hope.
Meanwhile Hinde has still greater dreams. “The big question is, how can we create elements 119 and 120?” To do this, however, a projectile heavier than 48Ca will need to be found. Hinde is working on identifying the best candidate.