Element 112 joins the periodic table

Tagged: periodic table, Technology
Source: newscientist - Read the full article
Posted: 4 years 35 weeks ago

Update: The International Union of Pure and Applied Chemistry has confirmed the name "Copernicium" for element 112 and given it the symbol Cn. The first choice for the chemical symbol, "Cp", apparently had other scientific meanings.

IN THE next few weeks, a new name will appear in the periodic table when the element with atomic number 112 receives a new name - sealing its place in the family of chemical elements. Known till now by the provisional name ununbium, element 112 will be named by its discoverers, a group led by Sigurd Hofmann at the Centre for Heavy Ion Research (GSI) in Darmstadt, Germany.

The naming of the new element will be the culmination of a long, fraught journey involving fierce competition, dashed hopes, clever detective work and even a brush with scientific misconduct. With a nucleus containing 112 protons - 20 more than uranium, the heaviest of the naturally occurring elements - it will be the weightiest atom whose existence has been confirmed so far. "The aim is to find the end of the periodic table," says Hofmann.
The naming of the new element will be the culmination of a long, fraught journey

The story of element 112 began in 1996, when Hofmann and his team reported that by firing a beam of zinc atoms at a piece of lead they had produced an atom that was embedded in their detector. Its nucleus decayed in several stages, releasing an alpha particle - composed of two neutrons and two protons - at each stage.

The alpha particle from the sixth decay had an energy and lifetime which matched those of an alpha particle from an atom of nobelium, the element which has atomic number 102. As the preceding five stages removed a total of 10 protons, Hofmann's team concluded that the nucleus of the original atom must have contained 112 protons.

There were some unanswered questions, however. For example, there appeared to be something wrong with the energy of the alpha particle emitted in the fifth stage of decay. The fifth alpha particle to be emitted should have come from rutherfordium (atomic number 104), yet the energy Hofmann's team observed was higher than that seen in previous experiments starting with rutherfordium.

The team also reported seeing a sequence of alpha particle emissions that stopped before reaching nobelium, suggesting they may have created a second atom of 112. However, inconsistencies between the two decay chains led the International Union of Pure and Applied Chemistry (IUPAC) to reject Hofmann's first bid to have the element recognised.

The following year things became clearer. Hofmann's team announced that when they examined their raw data files they could find no evidence for the shorter decay chain. They concluded that it had been "spuriously created" by a collaborator, Victor Ninov, and retracted that part of their 1996 report. "We were very angry," says Hofmann. "We still do not know why he did it." That year, Ninov was fired by Lawrence Berkeley National Laboratory (LBNL) in California after it emerged that he had manipulated a different set of results relating to another synthetic element, 118.

Hofmann's team also reran the experiment and submitted further evidence for element 112, but in 2003 IUPAC again rejected the claim on the grounds that the decay chain was different to the first and could not be repeated.

The clincher came in 2004, when a team led by Kosuke Morita at the RIKEN superheavy element laboratory in Wako, Japan, made two atoms of element 112. Combined with a later finding that there are two alpha decay paths that rutherfordium can take, this led IUPAC to finally recognise the existence of the new element (Pure and Applied Chemistry, DOI: 10.1351/PAC-REP-08-03-05).

Hofmann's retraction of Ninov's work was not the only controversy stirred up by element 112. In the late 1990s, a team led by Yuri Oganessian at the Joint Institute of Nuclear Research in Dubna, Russia, was trying to make heavier isotopes of element 112 - in which the nuclei contains more than the 165 neutrons in Hofmann's atom. In 1998, they announced that they had made such an isotope; this would be useful in verifying the creation of even heavier elements, just as Hofmann used nobelium to verify the presence of 112. But disappointment followed soon afterwards, when a group at LBNL could not reproduce the results.

Since then Oganessian has made atoms of neutron-rich 112 that have been independently confirmed. While Hofmann's atoms only last a fraction of a millisecond, the extra neutrons in these heavier nuclei gave them a half-life of 4 seconds, long enough to establish a crude value for the boiling point of element 112, about 80 °C (Nature, DOI: 10.1038/nature05761).

This convoluted sequence of events shows why IUPAC must be conservative about recognising an element, says Paul Karol of Carnegie Mellon University in Pittsburgh, Pennsylvania, who chaired the IUPAC panel that finally approved 112. "We are told that we are too slow, but this experience also gives us fuel for maintaining that position."