The Race for Rutherfordium

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in your element The race for rutherfordium mitch andré Garcia considers the disputed discovery of element 104 and takes a look at how the chemistry of this synthetic element is developing.

utherfordium, the 104th element tetravalent hafnium and zirconium tracers on the periodic table, was first and solidified its place as a group 4 metal. Rsynthesized artificially in the 1960s Gas-phase chemistry studies of and was the subject of international rutherfordium took advantage of the volatile controversy for decades. The dispute properties of the group 4 metal chlorides. centred on who should get to name the new Anyone who has worked with hafnium(iv) element. Historically, the discoverer of an chloride will no doubt remember the element is afforded the right to name it, but gag-inducing effect it has! Isothermal gas when two groups have competing discovery chromatography was performed with claims this becomes complicated. the chlorides of zirconium, hafnium and

The first research group to claim rutherfordium using a column of SiO2 from discovery of element 104 was a team of set temperatures of 100 °C to 600 °C (ref. 6). scientists at Dubna (in what was the USSR) The experiments measured the relative yields in 1964 (ref. 1). They observed an isotope of products out of the column as a function that underwent spontaneous fission after of temperature, and then the adsorption 242 bombarding their Pu target with a beam enthalpies on SiO2 from a Monte Carlo fit of 22 of Ne ions. A second team of scientists — One of the greatest achievements of Ernest their measurements were calculated. This was at Berkeley in California — tried for years Rutherford — for whom element 104 is named — used as a yard stick for measuring volatility. to replicate these experiments, but were was the destruction of the plum‑pudding model As expected for a heavier molecule, unable to do so. Finally, in 1969, the team at of the atomic nucleus. hafnium chloride was found to be less Berkeley made element 104 with a different volatile than zirconium chloride (that nuclear reaction; they used a target of 249Cf is, a lower enthalpy of adsorption than and a beam of 12C and 13C to produce 257Rf This outcome was not what either research zirconium chloride). However, the volatility and 259Rf (ref. 2). Both of these isotopes group wanted, but it was accepted with some of rutherfordium chloride was found to of rutherfordium decay into nobelium by protest. The name ‘rutherfordium’ was part be nearly the same as zirconium chloride. emitting α-particles. The characteristic decay of a broad set of compromises between both This is a dramatic break from the trend that energy and half-life of nobelium was also research groups that resulted in element periodicity would predict. Presumably this observed subsequent to the rutherfordium 105 being named for Dubna and element is caused by some relativistic effect, but the decays. Thus, the team at Berkeley was able 106 named for Glenn Seaborg. For more exact mechanism that creates volatile salts of to claim unambiguous detection of element information about the controversial history rutherfordium is still a mystery. 104 by following its chain of decays. of rutherfordium, see The Transuranium The future of rutherfordium chemistry will As the years went on neither group would People by Darleane Hoffman, Albert Ghiorso probably focus on devising chemical systems give ground, and finally an international and Glenn Seaborg3. that help elucidate the role of relativistic effects committee was assembled to determine In 1970, Ghiorso and co-workers in its chemistry, as well as the creation of new which claims had more weight. The synthesized a new isotope of rutherfordium, compound classes of rutherfordium, such as Transfermium Working Group (TWG) was 261Rf (ref. 4). The half-life of this particular inorganic complexes and organometallics. ❐ put together by the International Union isotope is 69 s — which is relatively long in of Pure and Applied Physics (IUPAP) and the context of transactinide elements — and Mitch ANdRé GARciA is at the University its sister chemistry organization IUPAC. so encouraged chemists to attempt the first of california, Berkeley, in the department of Although the TWG consisted of eminent liquid-phase studies of rutherfordium. At the chemistry, Berkeley, california 94720‑1460, scientists, none were heavy-element time it was not known whether rutherfordium USA. e‑mail: [email protected] scientists or radiochemists. would behave like a group 4 metal or would In 1992 the TWG finally released its follow the actinide series in its chemistry. In References findings. The committee decided that both the same year, Robert Silva and colleagues5 in 1. Flerov, G. N. et al. Phys. Lett. 13, 73–75 (1964). the Berkeley and Dubna groups should collaboration with Ghiorso’s team eluted 261Rf 2. Ghiorso, A. et al. Phys. Rev. Lett. 22, 1317–1320 (1969). 3. Hoffman, D. C., Ghiorso, A. & Seaborg, G. T. The Transuranium share the discovery claim for rutherfordium. from a cation exchange resin in the presence People: The Inside Story (Imperial College Press, 2000). of tetravalent zirconium and hafnium, and 4. Ghiorso, A. et al. Phys. Lett. B 32, 95–98 (1970). trivalent actinide tracers. The results of this 5. Silva, R. et al. Inorg. Nucl. Chem. Lett. 6, 871–877 (1970). experiment showed that 261Rf eluted with the 6. Kadkhodayan, B. et al. Radiochim. Acta 72, 169–178 (1996). Md No Lr Rf Db Sg Bh Hs Mt Ds Rg 112 113 114 115 116 117 118 119 120 121 66 nature chemistry | VOL 2 | JANUARY 2010 | www.nature.com/naturechemistry