in your element The darmstadtium cornerstone Dieter Ackermann explains why element 110 occupies a significant place in the superheavy corner of the periodic table.

he first isotope of darmstadtium to be region is characterized by enhanced nuclear synthesized was 269Ds, in November stability at atomic number 108 (hassium), 1994, through a cold fusion reaction and at neutron numbers 152 and 162, T 62 208 between Ni and Pb (ref. 1). The concept which are often called deformed sub-shell of cold fusion, where a nucleus is formed closures5. Towards higher atomic numbers in a fusion process at low excitation energy, and higher mass, theory predicts that had already been exploited successfully in nuclear deformation vanishes and the area of the hunt for superheavy nuclei by the team spherical nuclei, which should be stabilized working at the accelerator laboratory GSI in by quantum mechanical effects — referred to Darmstadt, Germany — the city that gave its as the ‘island of stability’ — will be reached6.

name to this element. PHOTO PETER SCHICKERT/ALAMY STOCK Its nuclear deformation is also the cause The team at GSI had already successfully of a striking feature of one of its isotopes, synthesized elements 107 (bohrium), The Darmstadtium conference centre in 270Ds, which represents the heaviest case of a 108 (hassium) and 109 (meitnerium) in Darmstadt holds a copy of the publication metastable state — referred to as a K isomer. 1981, 1984 and 1982, respectively. Ten years reporting the discovery of its eponymous element This state resembles a wobble stone with had elapsed, during which the group had in its cornerstone. an axis of total spin, which is inclined with improved the efficiency of their experimental respect to its symmetry axis, and whose set-up to cope with ever-lower probabilities decay is ‘forbidden’ by quantum mechanics. for the synthesis of ever-heavier elements. the fusing system across a complex potential It is more stable than the ground state — an To attempt the synthesis of element 110, it energy landscape. This concept — which had uncommon feature for nuclei. This is possibly was crucial to first measure the ‘excitation also constituted part of a controversial debate a first hint of some interesting physics, yet to function’ — a production probability as a within the GSI group during measurement be discovered, at the onset of the development function of energy — of the hassium isotope of the 266Hs excitation function3 — had failed towards the nuclear sphericity predicted 266Hs (Z = 108). An extrapolation then here, however. to occur in this area. In addition, these allowed the team to successfully predict the Experimental superheavy-element metastable states, depending on deformation, correct energy needed for the synthesis of chemistry is an extremely challenging have the potential to be tracers guiding us darmstadtium. undertaking and other, even heavier elements towards the ‘island of stability’7. The targeted isotope 269Ds was indeed seem to promise more exciting features than These interesting features make270 Ds one produced by fusion between 62Ni and 208Pb, darmstadtium. Therefore, this chemistry has of the cornerstones in the arc leading to the followed by ‘cooling down’ of the fused not been attempted yet and only theoretical superheavy elements. ❐ system through a one-neutron emission. predictions of the chemical properties But there was more: the team had enough of darmstadtium exist. They point to a DIETER ACKERMANN is at the Alternative time to change the projectile to 64Ni and different ground-state configuration than Energies and Atomic Energy Commission, synthesize a second isotope, 271Ds, and to that of its lighter homologues in group 10, at the Large Heavy Ion National Accelerator then go one step further. They exchanged but nevertheless a rather similar chemical Centre (GANIL), CEA-CNRS, Bd. Becquerel, the 208Pb foil that had served as the target behaviour. As for all the superheavy elements, 55027, F-14076 Caen, France. He is at for the previous two reactions to a 209Bi one, relativistic effects are of major importance present also supported by the European featuring one more proton, thus producing here. These effects arise from the acceleration Commission in the framework of the element 111 (roentgenium) in the same of the inner electrons to the highest velocities CEA-EUROTALENT programme. exciting run. in the strong Coulomb field created by the e-mail: [email protected] An earlier attempt to synthesize 271Ds many protons (here 110) in the heavy nucleus4. at higher beam energy had failed in 1985, In contrast to its chemistry, the physical References despite having applied a beam dose that was properties of darmstadtium — or rather of 1. Hofmann, S. et al. Z. Phys. A 350, 277–280 (1995). three times higher2. One of the reasons for its isotopes — have been experimentally 2. Münzenberg, G. et al. in GSI Scientific Report 1985, GSI Report the choice of the higher energy had been a studied, revealing some exciting nuclear 1986-1 (ed. Grundinger, U.) 29 (GSI, 1986). 3. Hofmann, S. On Beyond Uranium: Journey to the End of the concept called ‘extra push’, according to which structure features. The known darmstadtium Periodic Table (Taylor & Francis, 2002). an additional amount of energy may push isotopes sit on the edge of a region of 4. Türler, A. & Pershina, V. Chem. Rev. 113, 1237–1312 (2013). deformed nuclei in the Segrè chart — the 5. Ackermann, D. & Theisen, Ch. Phys. Scr. 92, 083002 (2017). 6. Cwiok, S., Heenen, P.-H. & Nazarewicz, W. Nature representation of nuclides as a function of 433, 705–709 (2005). their proton and neutron numbers. This 7. Ackermann, D. Nucl. Phys. A 944, 376–387 (2015). Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og 119 120 121 122 123 124 125 126 127 1034 NATURE CHEMISTRY | VOL 9 | OCTOBER 2017 | www.nature.com/naturechemistry ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.