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Home , Actinide concept, Lawrencium

in your element ’s place at the table Yuichiro Nagame ponders on the steps it took to make lawrencium, and its location in the .

he discovery — or, rather, the synthesis table as a new transition series directly below — of lawrencium spanned several the , lawrencium is the last of the Tyears and several experiments from and sits directly under . two research teams, in Berkeley, USA, and Yet despite — or owing to — recent advances in , Russia1. In 1961, the US-based in understanding lawrencium and lutetium, team first reported the synthesis of an a debate3 has emerged over their place in the of element 103. Mixed table: is it in the f-, d-block or p-block? isotope targets 249,250,251,252Cf were bombarded By analogy with lutetium, which has with beams; the reaction products an electronic structure of [Xe]4f 146s25d1, were caught by a metalized Mylar tape and the electronic configuration of lawrencium moved past a series of α-particle detectors. would be expected to be [Rn]5f 147s26d1. A new α-emitting nuclide with an energy of These configurations may place both 8.6 MeV and a half-life of approximately 8 s elements below and in was assigned to the isotope 257Lr. the d-block — a move supported by some Subsequent identification of chemical similarities between the four element 103 — though one that conflicted elements. Because of relativistic effects,

with the mass assignment of the Berkeley however, the 7p1/2 orbital of lawrencium team — came from Dubna in 1965, from is expected to be stabilized below the bombarding a 243Am target with a beam of 6d orbital, giving instead a revised 18 14 2 1 O ions. After sustained efforts on both configuration of [Rn]5f 7s 7p1/2 , which sides, conclusive identification of suggests it would also not be out of place in with mass numbers 255 through 260 the p-block.

finally came from Berkeley in 1971, from PHOTO / ALAMY STOCK LTD PRESS © PICTORIAL Recently, in our , the first ionization bombardments of 248Cm with 14N and energy of lawrencium was measured using 15N ions, and 249Cf with 10B and 11B ions. At present, twelve isotopes are known an efficient surface ion-source and a single- These results also confirmed most of with mass numbers 252–262 and 266 — the atom detection system coupled to a mass the previous reports, apart from the longest-lived one with a half-life of 11 h — separator4. A surprisingly low energy of identification of the first isotope created, as well as two metastable nuclear isomers 4.96 eV — lower than that of sodium — was which was in fact 258Lr. with mass numbers 253 and 255. found to be required to remove one The recognition of the new element Chemical studies of heavy elements from a neutral atom. This makes element also occurred in several steps. It was the with atomic numbers Z ≥ 100 are extremely 103 the easiest to ionize, and is Berkeley team who suggested the name difficult because the atoms exhibit short half- in excellent agreement with the predicted 14 2 1 lawrencium, with the symbol Lw, in honour lives and must be produced at accelerators, in [Rn]5f 7s 7p1/2 configuration. of Ernest O. Lawrence, inventor of the quantities of a few atoms, or often even one Nevertheless, these measurements can (pictured). The atom, at a time. Thus experimental procedures be taken to support lawrencium’s place as International Union of Pure and Applied must be repeated hundreds or thousands of an f-block actinide, a d-block transition Chemistry (IUPAC) approved the name times to give statistically significant results. or a p element, such that they have in 1971, though changed the symbol to Lr. The first chemical characterization came with not allowed the question of its location to In 1992, however, a Transfermium Working 256Lr as early as 1970, through a fast solvent be unambiguously settled, and lawrencium Group set up by IUPAC and IUPAP extraction technique1. Over 200 individual continues to create controversies. ❐ (International Union of Pure and Applied experiments, overall involving approximately Physics) re-evaluated all the reported data 1,500 lawrencium atoms, showed that it YUICHIRO NAGAME is at the Advanced and recommended that both the Berkeley exhibits a stable +3 in solution, Science Research Center, Japan Atomic and the Dubna teams should share credit for as expected for an actinide. The Energy Agency (JAEA), Tokai, Japan. the discovery of element 103 (ref. 2), leading of Lr3+ was first evaluated in 1988 through e-mail: [email protected] to their official recognition as co-discoverers cation-exchange chromatography with the 260 References in 1997. The name, by then commonly longer-lived isotope Lr, and its accuracy was 1. Silva, R. J. in The Chemistry of the Actinides and Transactinide accepted, remained unchanged. later improved to 0.0881 ± 0.0001 nm. Elements 3rd edn (eds Morss, L. R. et al.) 1621–1651 According to the (Springer, 2006). 2. Barber, R. C. et al. Prog. Part. Nucl. Phys. 29, 453–530 (1992). formulated by Seaborg, which placed the 3. Jensen, W. B. Found. Chem. 17, 23–31 (2015). 5f elements (Z = 89–103) in the periodic 4. Sato, T. K. et al. Nature 520, 209–211 (2015). Fm Md No Lr Rf Db Sg Bh Hs Mt Ds Rg Cn 113 Fl 115 Lv 117 118 119 120 282 NATURE CHEMISTRY | VOL 8 | MARCH 2016 | www.nature.com/naturechemistry

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