Elements 114 and 116 have been officially added to the periodic table, becoming its heaviest members yet. They both exist for less than a second before decaying into lighter atoms, but they bring researchers a step closer to making even heavier elements that are predicted to be stable for decades or longer, forming a fabled "island of stability" in the periodic table.
Evidence for the two elements has been mounting for years. They were finally given official status
as new elements on Wednesday, after a three-year review by the Joint
Working Party on Discovery of Elements, a committee of scientists from
the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP).
Several teams have claimed
to have produced element 114, starting in 1999. But the committee
decided that a series of experiments reported by a collaboration of two
teams in 2004 and 2006 provided the first convincing evidence. The same series of experiments is credited with producing evidence of element 116.
Slammed together
One of the collaborating groups was led by Yuri Oganessian at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, and the other by Ken Moody at the Lawrence Livermore National Laboratory in California.
The researchers forged the new heavy
elements by slamming together the nuclei of lighter atoms at an
accelerator at JINR. They made element 116 by bombarding targets made of
the radioactive element curium, which has 96 protons in its nucleus,
with calcium nuclei, which have 20 protons.
Nuclei of element 116 lasted only a few
milliseconds before spitting out an alpha particle made of two protons
and two neutrons and thereby decaying into nuclei of element 114. The
team also made element 114 directly by firing calcium nuclei at
plutonium targets, which have 94 protons in their nuclei.
Gone too soon
Element-114 nuclei decayed after about half a second into copernicium, which contains 112 protons, and is itself a very recent addition
to the periodic table, having officially joined only in 2009. It was
the pattern of time intervals between these decays, along with the
energy of the alpha particles produced, that clinched the case for the
elements' creation.
So what are elements 114 and 116 like?
Unfortunately, their properties are still murky because the quantities
produced were too small and existed too fleetingly for scientists to
measure their chemical behaviour, such as what other elements they tend
to react with.
"The lifetimes of these things have to be reasonably long so you can study the chemistry – meaning, pushing a minute," says Paul Karol of Carnegie Mellon University in Pittsburgh, who chaired the committee that approved the new elements.
'Not too weird'
As yet, the elements have no names. Instead
they go by the temporary placeholder terms ununquadium and ununhexium,
which by IUPAC convention are derived from the digits 114 and 116
respectively. Their discoverers will get a chance to offer suggestions
that another IUPAC committee will consider. "As long as it's not
something really weird, they will probably say it's fine," Karol told New Scientist.
The committee also considered discovery claims for elements 113, 115 and 118, but said in its report that the evidence it reviewed was not yet strong enough to warrant their addition to the periodic table.
Elements found to date at this extreme end
of the table are ephemeral, but nuclear theorists suspect a class of
super-heavy atoms could live for decades or longer and might boast
useful new chemical properties.
Karol says the discovery of elements 114 and 116 is exciting because it is a step towards this island of stability, which some predict may be centred on nuclei with 120 or 126 protons. "It's getting closer and closer," Karol says.
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