Ulrika Forsberg

Superheavy Element Flerovium (Element 114) Is a Volatile Metal

The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Experimental gas-solid chromatography studies on Cn have, indeed, revealed a metal-metal bond formation with Au. In contrast to this, for Fl, the formation of a weak bond upon physisorption on a Au surface was inferred from first experiments. Here, we report on a gas-solid chromatography study of the adsorption of Fl on a Au surface. Fl was produced in the nuclear fusion reaction (244)Pu((48)Ca, 3-4n)(288,289)Fl and was isolated in-flight from the primary (48)Ca beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear α-decay product Cn, their lighter homologues in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature in the first, isothermal part, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homologue in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.

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

Two short-lived isotopes ^{221}U and ^{222}U were produced as evaporation residues in the fusion reaction ^{50}Ti+^{176}Yb at the gas-filled recoil separator TASCA. An α decay with an energy of E_{α}=9.31(5)  MeV and half-life T_{1/2}=4.7(7)  μs was attributed to ^{222}U. The new isotope ^{221}U was identified in α-decay chains starting with E_{α}=9.71(5)  MeV and T_{1/2}=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.

High-precision mass measurements for the isobaric multiplet mass equation at A = 52

Masses of 52Co, 52Com, 52Fe, 52Fem, and 52Mn have been measured with the JYFLTRAP double Penning trap mass spectrometer. The isobaric multiplet mass equation for the T = 2 quintet at A = 52 has been studied employing the new mass values. No significant breakdown (beyond the level) of the quadratic form of the IMME was observed (). The cubic coefficient was 6.0(32) keV (). The excitation energies for the isomer and the T = 2 isobaric analog state in 52Co have been determined to be 374(13) keV and 2922(13) keV, respectively. The measured mass values for 52Co and 52Com are 29(10) keV and 16(15) keV higher, respectively, than obtained in a recent storage-ring experiment, and significantly lower than predicted by extrapolations. Consequently, this has an impact on the proton separation energies for 52Co and 53Ni relevant for the astrophysical rapid proton capture process. The Q value for the proton decay from the isomer in 53Co has been determined with an unprecedented precision, keV. (Less)

Nuclear Structure Notes on Element 115 Decay Chains

Hitherto collected data on more than hundred α-decay chains stemming from element 115 are combined to probe some aspects of the underlying nuclear structure of the heaviest atomic nuclei yet created in the laboratory.

Identification of Reaction Products in 50Ti+249Cf Reactions at TASCA

The neutron-rich nuclei 33P and 33S in the upper sd-shell were investigated by means of the 26Mg(13C,npa) and 26Mg(13C,2na) fusion-evaporation reactions. Excited states with intermediate and high spins have been populated. The level schemes of both nuclei have been considerably extended. Utilizing the gammagamma-angular correlation method the spin-parity assignment of the new excited states in 33P has been investigated. The experimentally determined energy levels as well as the known reduced transition probabilities (i.e. B(M1) and B(E2) values) from both nuclei were compared to 0hbaromega and 1hbaromega truncated p-sd-pf shell-model calculations using the PSDPF interaction. For the energy levels a very good agreement between experiment and theory was shown for both 33P and 33S. However, for B(M1) and B(E2) values the calculated values cannot reproduce the experimental results with satisfying agreement for all transitions. In some places the discrepancy between experiment and theory is even large, which requires further experimental as well as theoretical investigation of this thesis for these nuclei. The second part was focused on the upgrade and commissioning tests of the Lund- York-Cologne CAlorimeter (LYCCA). As a key device of the High resolution In-flight SPECtroscopy (HISPEC) campaign of the FAIR/NUSTAR collaboration, LYCCA was designed to identify the reaction products after the secondary target, as well as to track the particle trajectory event by event. After the successful employment of the precursor LYCCA-0 in the PreSPEC campaign, the electronic as well as mechanic components of the LYCCA system were upgraded by STFC Daresbury Laboratory. Using the high integrated AIDA Front-End electronics with ASICs the signals from more than thousand DSSSD-channels were pre-amplified and processed. Since 2016, the new LYCCA setup is located at the Cologne tandem accelerator. Triple-Alpha tests and in-beam experiments of elastic scattering were carried out to check the specifications of the system after the upgrade. The obtained results allow first important conclusions about energy resolution and efficiency of the calorimeter at low energies for future NUSTAR experiments.Di Nitto, A.; Khuyagbaatar, J.; Ackermann, D.; Adamczewski-Musch, J.; Andersson, LiseLotte; Badura, E.; Block, M; Brand, H.; Cox, D. M.; Düllmann, Ch. E.; Dvorak, J.; Eberhardt, K.; Ellison, P. A.; Esker, N. E.; Even, J.; Fahlander, Claes; Forsberg, Ulrika; Gates, J.M.; Golubev, Pavel; Gothe, O.; Gregorich, K.E.; Hartmann, W.; Herzberg, R.-D.; Heßberger, F. P.; Hoffmann, J.; Hollinger, R.; Hübner, A.; Jäger, E.; Jeppsson, J.; Kindler, B.; Klein, S.; Kojouharov, I.; Kratz, J.V.; Krier, J.; Kurz, N.; Lahiri, S.; Linev, S.; Lommel, B.; Maiti, M.; Mändl, R.; Merchán, E.; Minami, S.; Mistry, A. K.; Mokry, Ch.; Nitsche, H.; Omtvedt, J. P.; Pang, G.; Pysmenetska, I.; Renisch, D.; Rudolph, Dirk

Recoil-alpha-fission and Recoil-alpha-alpha-fission Chains Stemming from Element 115

Rudolph, Dirk; Forsberg, Ulrika; Düllmann, C. E.; Golubev, Pavel; Heßberger, F.P.; Khuyagbaatar, J.; Kratz, J. V.; Sarmiento, Luis; Yakushev, A.; Ackermann, D.; Andersson, L.; Block, M.; Brand, H.; Cox, D.; Derkx, X.; Di Nitto, A.; Eberhardt, K.; Even, J.; Fahlander, Claes; Gates, J. M.; Gerl, J.; Gregorich, E. K.; Gross, C. J.; Herzberg, R.-D.; Jäger, E.; Kindler, B.; Krier, J.; Kojouharov, I.; Kurz, N.; Lommel, B.; Mistry, A.; Mokry, C.; Nitsche, H.; Omtvedt, J. P.; Papadakis, P.; Runke, J.; Rykaczewski, K.; Schädel, M.; Schaffner, H.; Schausten, B.; Thörle-Pospiech, P.; Torres, T.; Traut, T.; Trautmann, N.; Türler, A.; Ward, A.; Wiehl, N. Published in: GSI Report

Element 115 Studied with TASISpec

D. Rudolph1, U. Forsberg1, P. Golubev1, L.G. Sarmiento1, A. Yakushev2, L.-L. Andersson3, A. Di Nitto4, Ch.E. Dullmann2,3,4, J.M. Gates5, K.E. Gregorich5, C.J. Gross6, R.-D. Herzberg7, F.P. Hesberger2,3, J. Khuyagbaatar3, J.V. Kratz4, K. Rykaczewski6, M. Schadel2,8, S. ◦ Aberg1, D. Ackermann2, M. Block2, H. Brand2, B.G. Carlsson1, D. Cox7, X. Derkx3,4, K. Eberhardt3,4, J. Even3, C. Fahlander1, J. Gerl2, E. Jager2, B. Kindler2, J. Krier2, I. Kojouharov2, N. Kurz2, B. Lommel2, A. Mistry7, C. Mokry3,4, H. Nitsche5, J.P. Omtvedt9, P. Papadakis7, I. Ragnarsson1, J. Runke2, H. Schaffner2, B. Schausten2, P. Thorle-Pospiech3,4, T. Torres2, T. Traut4, N. Trautmann4, A. Turler10, A. Ward7, D.E. Ward1, and N. Wiehl3,4 1Lund University, Lund, Sweden; 2GSI Helmholtzzentrum fur Schwerionenforschung GmbH, Darmstadt, Germany; 3Helmholtz Institute Mainz, Mainz, Germany; 4Johannes Gutenberg-Universitat Mainz, Mainz, Germany; 5Lawrence Berkeley National Laboratory, Berkeley, USA; 6Oak Ridge National Laboratory, Oak Ridge, USA; 7University of Liverpool, Liverpool, United Kingdom; 8Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan; 9University of Oslo, Oslo, Norway; 10Paul Scherrer Institute and University of Bern, Villigen, Switzerland