GSI Experiments on Synthesis and Nuclear Structure Investigations of Heaviest Nuclei F. P. Heßberger Gesellschaft für Schwerionenforschung mbH, D-64291 Darmstadt, Germany XII Nuclear Physics Workshop Maria and Pierre Curie Nuclear Structure Physics and Low Energy Reactions 21.-25. September 2005, Kazimierz Dolny, Poland

Experimental Set-up at GSI GSI Experiments on Search for SHE Outline of the talk Physical Motivation Experimental Set-up at GSI GSI Experiments on Search for SHE GSI Experiments on Nuclear Structure Investigations of Transfermium Isotopes -- Decay Studies of odd-mass odd-Z nuclei -- Decay Studies of odd-mass even-Z nuclei -- Systematic Trends in Single Particle Levels -- K-Isomers in even-even nuclei • Conclusions • Collaborations

Predictions of Superheavy Elements 126 126 114 114 82 82 184 184 (164) (164) 126 126 H. Meldner Arkiv fys. 36,593 (1967)

114 82 d5/2 j15/2 9/2-[734] g9/2 100 96 f5/2 7/2+[624] f7/2 i13/2 h9/2 184 f5/2 7/2-[514] d5/2 7/2+[624] 114 114 j15/2 152 f7/2 1/2-[521] 9/2-[734] g9/2 i13/2 100 142 h9/2 3/2-[521] 96 134 126 7/2+[633] 1/2+[631] 82 Nilsson – Diagrams for Neutron (left) and proton (right) single particle levels

Production Mechanisms Excerpt from Chart of Nuclei Study of Production Mechanisms Search for SHE Nuclear Structure Investigations

Velocity separator SHIP Separation time: 1 – 2 μs Transmission: 20 – 50 % Background: 10 – 50 Hz Det. E. resolution: 18 – 25 keV Det. Pos. resolution: 150 μm Dead time: 25 μs Mastertitelformat bearbeiten

Synthesis of SHE

confirmed - - disproved Basic Rule in Physics: Experimental results have to be reproduced independently before being generally accepted Reaction 238U(48Ca,xn) 276-x112 are technically ‚easy‘ to perform  a ‚key‘ to SHE E* / MeV Dose/10-19 events T1/2 /s σ/pb Vassilissa 33 0.35 2 (ER-sf) 81 5.0 (Oganessian et al.) 39 0.22 <7.3 0.59 <2.2 35.5 0.47 568 3.0 DGFRS 31.4 0.58 1 (ER-[α]-sf) 3.4 0.5 +1.2/-0.4 (3n) 35.0 0.71 2 (ER-[α]-sf 3 (ER- α-sf) 1 (ER- 4α-sf) 1.4 2.7 6.1 2.5 +1.8/-1.1 (3n) 39.8 0.52 1 (ER-sf) 0.14 (ms) 0.6 +1.6/-0.6 (4n) Chemistry (Yakushev et al.) 34.2 0.28 7 sf >60 ≈2 BGS (Loveland, 31.9 0.226 - <0.8 Gregorich et al.) 36.9 0.185 <0.96 SHIP 32.0 0.7 (Hofmann et al.) 34.5 1.0 5.2 0.7 +1.6/-0.6 37.0 1.2 <0.6 failed to confirm confirmed - - disproved

Nuclear Structure Investigations of Transfermium Isotopes What can be (presently) achieved by decay studies ? Production rates: 207Pb(48Ca,2n)253No : σ ≈ 900 nb, i(48Ca) ≈ 1pμA  z α ≈ 7000 /h  206Pb(48Ca,3n)251No : σ ≈ 25 nb, i(48Ca) ≈ 1pμA  zα ≈ 200 /h 207Pb(50Ti,2n)255Rf : σ ≈ 10 nb (50% sf), i(50Ti) ≈ 0.4pμA  zα ≈ 20/h 209Bi(40Ar,2n)247Md : σ ≈ 7 nb, i(40Ar) ≈ 1.5pμA  zα ≈ 40 /h Collection of several (ten) thousand decays within several days Fine structure measurements possible, but not sufficient for detailed level schemes (like for nuclei where weighable amounts are available) Establishing global trends in nuclear structure (for some Nilsson levels) Similarities in Nuclear Structure along the ‚Isotope Line‘ in odd-Z nuclei Similarities in Nuclear Structure along the ‚Isotone Line‘ in even-Z nuclei

Nuclear Structure Investigation of odd-A odd-Z nuclei

Comparison of theoretical and experimental Nilsson levels of odd mass Es - isotopes a) Calculations of Cwiok et al. (black) and Parkhomenko and Sobiczewski (red) b) experimental values Trend of increasing energy with increasing N satisfactoily reproduced by Cwiok et al. but maximum at Es-249 Opposite trend predicted by Parkhomenko and Sobiczewski Ground state predicted as 7/2+[633]; situation not fully clear from experimental side Energies of the 7/2-[514] – levels differ by several hundreds of keV

Deformation of odd-mass Es-isotopes as function of mass number Evidently: Relation between energy of 7/2- [514] level and deformation

Nuclear Structure Investigation of odd-A even-Z nuclei Example: Alpha-gamma decay measurements of 251No and its daughter products

Alpha – gamma – gamma coincidence measurements of 247Fm  coincidences between K-x-rays  two transitions E > 136 keV  coincidences of K-x-rays with 121.9 keV and 166.3 keV  121.9 keV coincident with x-rays, 141.8 keV but not with 166.3 keV, which has a higher intensity than the 141.8 keV line

Attempt to assign ‚gamma‘ – pairs to transitions:

(energies of gamma lines may differ slightly from values on preceding foils)

Nilsson-Level systematics of N=151 isotones (even Z)

Nilsson - Level systematics of N=149 Isotones (even Z)

Nilsson-Level systematics of N = 147 Isotones (even Z)

Identifikation of a K-Isomer in 254No (R. Herzberg et al. , Exp Identifikation of a K-Isomer in 254No (R.Herzberg et al., Exp. at RITU, Jyväskylä) 184 μs 266 ms Spectra from confirmation experiment at SHIP 06/05

Identification of an isomeric state in 252No gamma energies in keV

Conclusions ☺ Experimental results presently available ☺ ‘Cold’ fusion reactions have been a successful method to produce isotopes of elements up to Z = 113; however, cross sections decrease drastically with increasing atomic num- ber;for element 113 only 0.055 pb were measured (but probably not the maximum) ☺ ‘Hot’ fusion reactions may be a suited method to produce SHE; interesting results have been obtained from DGFRS, but could not be confirmed in other laboratories so far; more effort is needed ☺ To better understand the properties of heaviest known nuclei and to get a firm base for reliable predictions of nuclear properties in the expected region of (spherical) superheavy nuclei detailed investigations of nuclear structure are indispensable; experimental tools are α -γ- (α –CE)-decay spectroscopy or in-beam spectroscopy ☺ Experimental results presently available  allow to follow systematics in the energy of single particle levels in N = 145, 147, 149 and 151 isotones with even atomic numbers up to Z = 102  indicated close similarities in the nuclear structure of neutron deficient isotopes with even neutron numbers of odd Z elements in the region einsteinium to dubnium ☺ Production rates indicate, that detailed nuclear structure investigations by means of - - coincidence measurements are possible with present techniques down to cross sections of 100pb (265Hs)  ‘On and on but the road is never ending, at least we know, we’re on our way’ (from ‘On and on’ by Fiddler’s Green)

Collaboration GSI, Darmstadt S. Hofmann, D. Ackermann, B. Kindler, I.Kojouharov, P. Kuusiniemi, B. Lommel, R. Mann, K. Nishio, B. Sulignano, F.P.H University Bratislava, Slovakia S. Antalic, S. Saro, B. Streicher, M. Venhart, P. Cagarda (until 2003) University Jyväskylä, Finland M. Leino, J. Uusitalo FLNR-JINR Dubna, Russia A.G. Popeko, A.N. Eremin University Liverpool, UK R.-D. Herzberg University Warsaw, Poland A. Sobiczewski, A. Parkhomenko