in your element Welcome copernicium? in the search for superheavy elements, element 112 was a stepping stone towards the ‘islands of stability’. sigurd hofmann now relates the steps that led to its ‘creation’ and detection.

lement 112 did not invite a lot of element 112 in one week. In 2000, a second interest when theoretical nuclear experiment allowed us to measure a second Ephysicists predicted the famous island atom, and two more atoms were produced of stable superheavy elements — elements in 2004 by the RIKEN laboratory in Japan that have a number of nucleons that leads (K. Morita et al. J. Phys. Soc. Jpn. 76, 043201; to arrangements in closed shells, which 2007), thus confirming our data. This led confers them stability despite the high the International Union of Pure and Applied repulsion forces between the protons. Rather Chemistry to assign priority of its discovery than element 112, it was element 126, and to our team, and in April 2009 we were later 114 and 120, that attracted most of asked to suggest a name for element 112. the attention, because they were predicted Our team of 21 researchers from four to have half-lives up to a million years, different nations discussed possible names

suggesting that they could be found on LICKI for about a month — including those

Earth. Efforts to identify them in nature or in z Ku suggested by students and the public. We S a

various nuclear reactions, however, remained K agreed that element 112 should be named unsuccessful, leading scientists to follow after the astronomer Nicolaus Copernicus the difficult and stony path of producing and suggested the name ‘copernicium’ with these elements step-by-step. In 1976, the the abbreviation ‘Cn’. starting point was element 106, now called Copernicus, who lived 500 years ago in the seaborgium, and for many years element 112 transition period between the Middle Ages marked a temporary end to this progress. / Lu © ISTOCKPHOTO and modern times, had a significant influence Four key technical improvements were nicolaus Copernicus is best known for on the political and philosophical thinking required to enable the detection of 112. The challenging the accepted view of the Universe at that time and contributed to the rise of first was an accelerator delivering ion beams by describing a system centred around the Sun, modern science, based on experiments. His of as many different isotopes as possible, with rather than the Earth. representation of the planets also represents beam intensities of at least 1012–1013 ions other systems governed by an attractive force per second, and at about 10% of the speed between small objects revolving around a of light. The second was a target, also made material so that the sum of their protons gave bigger centre. On a microscopic scale, this is from various isotopes, which could stand 112: a zinc beam consisting of 30 protons the atom, with its electrons orbiting around these high beam intensities. The third was and 40 neutrons was used to bombard lead the nucleus and, in the case of copernicium, a separator for fast and efficient separation target nuclei, composed of 82 protons and 112 electrons moving around a nucleus of the reaction products from the beam, 126 neutrons, resulting in a new element that consisting of 112 protons and 165 neutrons. and finally a detector system for a reliable had 112 protons and 166 neutrons — that is, Copernicium should behave as a identification of the element obtained. an atomic-mass number of 278. transition metal, as it is below zinc, cadmium In our laboratory, these advances were Although forcing the two nuclei (zinc and and mercury in group 12, and its similarity made possible with the accelerator UNILAC lead) together requires a considerable amount to the latter has already been shown by initial (Universal Linear Accelerator), a rotating of energy — the reacting nuclei do not easily experiments adsorbing a few atoms of it onto target wheel, the electromagnetic separator amalgamate, and are much more likely to be a gold surface. It might be a little bit more SHIP (Separator for Heavy Ion reaction repulsed by immensely strong electric forces volatile than mercury, but will very likely be Products) and the use of position-sensitive acting between their protons — this barrier a liquid at room temperature. Of course, with silicon detectors. This combination allowed can be overcome and the attractive force only a few rapidly decaying atoms having us to detect nuclei with lifetimes ranging between the nuclei leads to nuclear fusion. been made so far, it is not likely to be of from one microsecond to a few hours, and This reaction releases energy, and the hot practical use for some time, but its detection detect each element from 107 to 111. In nucleus created by this exothermic process paves the way to heavier elements still — the 1996 we were ready to synthesize element then cools down by emitting one neutron, aforementioned superheavy elements. ❐ 112. We selected a beam and a target and the nucleus 277 remains, which is the one we were able to study. SigURd HOFmAnn is at the Heavy ion Even with the most intensive beams, Research Centre (gSi) in darmstadt, we managed to produce only one atom of germany. e-mail: [email protected] Mt Ds Rg 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 146 nature chemistry | VOL 2 | FEBRUARY 2010 | www.nature.com/naturechemistry

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