Research Program - Highlights


New Short-Lived Isotope 221U and the Mass Surface Near N = 126

J. Khuyagbaatar, A. Yakushev, Ch. E. Düllmann, D. Ackermann, L.-L. Andersson, M. Block, H. Brand, D. M. Cox, J. Even, U. Forsberg, P. Golubev, W. Hartmann, R.-D. Herzberg, F. P. Heßberger, J. Hoffmann, A. Hübner, E. Jäger, J. Jeppsson, B. Kindler, J. V. Kratz, J. Krier, N. Kurz, B. Lommel, M. Maiti, S. Minami, A. K. Mistry, Ch.M. Mrosek, I. Pysmenetska, D. Rudolph, L. G. Sarmiento, H. Schaffner, M. Schädel, B. Schausten, J. Steiner, T. Torres De Heidenreich, J. Uusitalo, M. Wegrzecki, N. Wiehl, and V. Yakusheva

Two short-lived isotopes 221U and 222U were produced as evaporation residues in the fusion reaction 50Ti + 176Yb at the gas-filled recoil separator TASCA. An α decay with an energy of Eα = 9.31(5) MeV and half-life T½ = 4.7(7) μs was attributed to 222U. The new isotope 221U was identified in α-decay chains starting with Eα = 9.71(5) MeV and T½ = 0.66(14) μs leading to known daughters. Synthesis and detection of these unstable heavy nuclei and their descendants were achieved thanks to a fast data readout system. The evolution of the N = 126 shell closure and its influence on the stability of uranium isotopes are discussed within the framework of α-decay reduced width.

Article:
Physical Review Letters 115, 242502 (2015) – Published 10 December 2015

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Measurement of the First Ionization Potential of Lawrencium,
Element 103

T. K. Sato, M. Asai, A. Borschevsky, T. Stora, N. Sato, Y. Kaneya, K. Tsukada, Ch. E. Düllmann, K. Eberhardt, E. Eliav, S. Ichikawa, U. Kaldor, J. V. Kratz, S. Miyashita, Y. Nagame, K. Ooe, A. Osa, D. Renisch, J. Runke, M. Schädel, P. Thörle-Pospiech, A. Toyoshima & N. Trautmann

The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row — including the actinides — even affecting ground-state configurations. Atomic s and p1/2 orbitals are stabilized by relativistic effects, whereas p3/2, d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP1) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by the difficulty in obtaining the heaviest elements on scales of more than one atom at a time. Here we report that the experimentally obtained IP1 of the heaviest actinide, lawrencium (Lr, atomic number 103), is 4.96 electronvolts. The IP1 of Lr was measured with 256Lr (halflife, 27 seconds) using an efficient surface ion-source and a radioisotope detection system coupled to a mass separator. The measured IP1 is in excellent agreement with the value of 4.963(15) electronvolts predicted here by state-of-the-art relativistic calculations.The present work provides a reliable benchmark for theoretical calculations and also opens the way for IP1 measurements of superheavy elements on an atom-at-a-time scale.

Article:
Nature 520, 209-211 (2015)

"News & Views" by Prof. Andreas Türler:
Nuclear chemistry: Lawrencium bridges a knowledge gap
Nature 520, 166-167 (2015)

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Seaborgium Hexacarbonyl Sg(CO)6: First Carbonyl Complex of a Superheavy Element

Synthesis and Detection of a Seaborgium Carbonyl Complex

J. Even, A. Yakushev, Ch.E. Düllmann, H. Haba, M. Asai, T.K. Sato, H. Brand, A. Di Nitto, R. Eichler, F.L. Fan, W. Hartmann, M. Huang, E. Jäger, D. Kaji, J. Kanaya, Y. Kaneya, J. Khuyagbaatar, B. Kindler, J.V. Kratz, J.Krier, Y. Kudou, N. Kurz, B. Lommel, S. Miyashita, K. Morimoto, K. Morita, M. Murakami, Y. Nagame, H. Nitsche, K. Ooe, Z. Qin, M. Schädel, J. Steiner, T. Sumita, M. Takeyama, K. Tanaka, A. Toyoshima, K. Tsukada, A. Türler, I. Usoltsev, Y. Wakabayashi, Y. Wang, N. Wieh, S. Yamaki

Experimental investigations of transactinoide elements provide benchmark results for chemical theory and probe the predictive power of trends in the periodic table. So far, in gas-phase chemical reactions, simple inorganic compounds with the transactinoide in its highest oxidation state have been synthesized. Single-atom production rates, short half-lives, and harsh experimental conditions limited the number of experimentally accessible compounds. We applied a gas-phase carbonylation technique previously tested on short-lived molybdenum (Mo) and tungsten (W) isotopes to the preparation of a carbonyl complex of seaborgium, the 106th element. The volatile seaborgium complex showed the same volatility and reactivity with a silicon dioxide surface as those of the hexacarbonyl complexes of the lighter homologs Mo and W. Comparison of the product’s adsorption enthalpy with theoretical predictions and data for the lighter congeners supported a Sg(CO)6 formulation.

Article:
Science 345, 1491 (2014)

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Element 117

Study of the 48Ca + 249Bk Fusion Reaction Leading to Element Z=117: Long-Lived α-Decaying 270Db and Discovery of 266Lr

J. Khuyagbaatar, A. Yakushev, Ch.E. Düllmann, D. Ackermann, L.-L. Andersson, M. Asai, M. Block, R.A. Boll, H. Brand, D.M. Cox, M. Dasgupta, X. Derkx, A. Di Nitto, K. Eberhardt, J. Even, M. Evers, C. Fahlander, U. Forsberg, J.M. Gates, N. Gharibyan, P. Golubev, K.E. Gregorich, J.H. Hamilton, W. Hartmann, R.-D. Herzberg, F.P. Hessberger, D.J. Hinde, J. Homann, R. Hollinger, A. Hübner, E. Jäger, B. Kindler, J.V. Kratz, J. Krier, N. Kurz, M. Laatiaoui, S. Lahiri, R. Lang, B. Lommel, M. Maiti, K. Miernik, S. Minami, A. Mistry, C. Mokry, H. Nitsche, J.P. Omtvedt, G.K. Pang, P. Papadakis, D. Renisch, J. Roberto, D. Rudolph, J. Runke, K. Rykaczewski, L.G. Sarmiento, M. Schädel, B. Schausten, A. Semchenkov, D.A. Shaughnessy, P. Steinegger, J. Steiner, E.E. Tereshatov, P. Thörle-Pospiech, K. Tinschert, T. Torres De Heidenreich, N. Trautmann, A. Türler, J. Uusitalo, D.E. Ward, M. Wegrzecki, N. Wiehl, S.M. Van Cleve, and V. Yakusheva

The superheavy element with atomic number Z=117 was produced as an evaporation residue in the 48Ca + 249Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-µs and a few days. Two decay chains comprising seven decays and a spontaneous ssion each were identified and are assigned to the isotope 294117 and its decay products. A hitherto unknown α-decay branch in 270Db (Z=105) was observed, which populated the new isotope 266Lr (Z=103). The identification of the long-lived (T1/2 = 1.0 (+1.9/-0.4) h) α-emitter 270Db marks an important step towards the observation of even more long-lived nuclei of superheavy elements located on an "island of stability".

Article:
Phys. Rev. Lett. 112, 172501 (2014)
Synopsis: Element Z=117 Confirmed

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Element 115

Spectroscopy of Element 115 Decay Chains

D. Rudolph, U. Forsberg, P. Golubev, L. G. Sarmiento, A. Yakushev, L.-L. Andersson, A. Di Nitto, Ch. E. Düllmann, J. M. Gates, K. E. Gregorich, C. J. Gross, F. P. Heßberger, R.-D. Herzberg, J. Khuyagbaatar, J. V. Kratz, K. Rykaczewski, M. Schädel, S. Åberg, D. Ackermann, M. Block, H. Brand, B. G. Carlsson, D. Cox, X. Derkx, K. Eberhardt, J. Even, C. Fahlander, J. Gerl, E. Jäger, B. Kindler, J. Krier, I. Kojouharov, N. Kurz, B. Lommel, A. Mistry, C. Mokry, H. Nitsche, J. P. Omtvedt, P. Papadakis, I. Ragnarsson, J. Runke, H. Schaffner, B. Schausten, P. Thörle-Pospiech, T. Torres, T. Traut, N. Trautmann, A. Türler, A. Ward, D. E. Ward, and N. Wiehl

Phys. Rev. Lett. 111, 112502 (2013)
Synopsis: Element 115 Confirmed

A high-resolution α, x-ray, and γ-ray coincidence spectroscopy experiment was conducted at the GSI Helmholtzzentrum für Schwerionenforschung. Thirty correlated α-decay chains were detected following the fusion-evaporation reaction 48Ca + 243Am. The observations are consistent with previous assignments of similar decay chains to originate from element Z=115. For the first time, precise spectroscopy allows the derivation of excitation schemes of isotopes along the decay chains starting with elements Z>112. Comprehensive Monte Carlo simulations accompany the data analysis. Nuclear structure models provide a first level interpretation.

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New superheavy elements can be uniquely identified
Further Information about element 115 (Lund Univ.)
Element 115 Experiment Reaches APS Top Ten List of "Physics Newsmakers of 2013"