Investigating the Atomic and Nuclear Properties of the Heaviest - PowerPoint PPT Presentation

GSI Colloquium 19.05.2015 Investigating the Atomic and Nuclear Properties of the Heaviest Elements Michael Block GSI Darmstadt Helmholtzinstitut Mainz Institut für Kernchemie der Universität Mainz

Outline Status of superheavy element (SHE) research • Basics of Penning trap mass spectrometry (PTMS) • Direct mass measurements of nobelium and lawrencium isotopes • New developments and selected results related to neutrino physics • Basics of resonance ionization laser spectroscopy (RIS) • Experimental efforts towards RIS of 254 No at GSI • Summary and conclusions •

SHIPTRAP Collaborators D. Ackermann, K. Blaum, S. Chenmarev, C. Droese, Ch. Duellmann, M. Eibach, S. Eliseev, P. Filanin, F. Giacoppo, M. Goncharov, E. Haettner, F. Herfurth, F. P. Heßberger, O. Kaleja, M. Laatiaoui, G. Marx, D. Nesterenko, Yu. Novikov, W. R. Plaß, S. Raeder, D. Rodríguez, 2010 D. Rudolph, C. Scheidenberger, S. Schmidt, L. Schweikhard, P. Thirolf, G. Vorobjev , C. Weber, …

‏ Laser Spectroscopy Collaborators D. Ackermann, M. Block, M. Laatiaoui, S. Raeder F.P. Heßberger P. Kunz H. Backe, W. Lauth R. Ferrer, P. Van Duppen F. Lautenschläger, P. Chhetri, Th. Walther B. Cheal, C. Wraith Former members: E. Minaya Ramirez, J. Even, Ch. Droese

Superheavy Elements – Present Status and Key Questions

Nuclear Chart SHE Proton Number Z ≈ 3,000 nuclides known • ≈ 250 stable nuclides • ≈ 7,000 nuclides predicted to exist • Neutron Number N

Superheavy Nuclei (SHN) saddle point ground state (spherical) macroscopic E pot fission barrier Deformation fission barrier in liquid drop model vanishes for Z ≈ 106 • stabilization against spontaneous fission by nuclear shell effects • superheavy nuclei owe their very existence to shell effects

Superheavy Nuclides – Current Landscape 120 Z Lv a Fl 114 a Cn a Rg Ds a Mt 108 Hs a Bh SF ??? ??? a b + 184 100 EC b - N 152 162 172 Courtesy Ch.E. Düllmann

Nuclear Shells: Magic Numbers in SHE? M. Bender et al., Phys. Lett. B 515 (2001) 42

Importance of Masses for Z > 100 high-precision mass measurements provide • accurate absolute binding energies to map nuclear shell effects • anchor points to fix decay chains ➡ Studies the nuclear structure evolution ➡ Benchmark theoretical nuclear models

Atomic Physics Studies of the Heaviest Elements 1 18 1 2 H 2 13 14 15 16 17 He 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 11 12 13 14 15 16 17 18 Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 57+ * 55 56 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 89+ " 87 88 104 105 106 107 108 112 114 chemistry with Fr Ra Ac Rf Db Sg Bh Hs 109 110 111 Cn 113 Fl 115 116 117 118 single atoms Mt Ds Rg --- --- Lv --- --- * 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Lanthanides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu " 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Actinides Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr • study atomic structure and architecture of periodic table • affected by strong relativistic effects and QED • benchmark theoretical calculations

Relativistic Effects in Uranium { 6d 3/2 , 6d 5/2 7p 1/2 , 7p 3/2 0 7s 1/2 , 7s expansion of 6d 5f -10 7/2 d, f orbitals 5f 5/2 5f -20 6p 6p 3/2 -30 E [eV] contraction of 6p 1/2 s 1/2 , p 1/2 orbitals -40 6s -50 6s -60 1/2 Spin-orbit non-relativistic relativistic c  coupling finite c J. P. Desclaux, At. Data Nucl. Data Tables 12 (1973) 311

Laser Spectroscopy of the Heaviest Elements Search for atomic hyperfine Measurement of Methods: levels spectroscopy isotopic shifts relativistic and Nuclear changes in mean Motivation: QED effects moments & square charge radii spins adapted from B. Cheal

Laser spectroscopy – Status of Measurements Measured since 1995 Measured prior to 1995 Figure from B. Cheal and K.T. Flanagan, J. Phys. G. 37 (2010) 113101

Superheavy Elements – Key Questions Where is the end of the periodic table in atomic number and mass? • What is the heaviest element that we can synthesize? • What are the properties and boundaries of the predicted ”island of stability” of • superheavy elements? What are the details of the fission process and competing decay modes? • Are there remnants of long-lived superheavy elements on earth? • How do relativistic effects affect the architecture of the periodic table? • SHE research at GSI/HIM follows a comprehensive approach investigating atomic, chemical, and nuclear properties of SHE

Future Directions in SHE Research at GSI 120 Z 114 108 SF a 184 b + 100 EC b - N 172 152 162 Courtesy Ch.E. Düllmann

Production of the Heaviest Elements

Requirements – Some Facts and Figures Beam intensity: present: 6 x 10 12 pps (1 m A p ) for typical beams 48 Ca, 50 Ti, … • future: ≥6 x 10 13 pps (10 m A p ) feasible •  need for high-power targets Targets: 0.5-1.0 mg/cm 2 thickness • about 10 mg of material needed for typical target wheel geometries •  limited availability of actinide material Recoil separator High transmission, short separation time • low background (beam suppression, low n, g background) •

Cross Sections for SHE Production 1E-6 Projectile Target 48 Ca,..., 70 Zn + 208 Pb/ 209 Bi 1E-7 13 C,..., 26 Mg + 238 U... 249 Bk cross section / barn 48 Ca + 238 U,..., 249 Cf 1E-8 1E-9 Due to low intensities radioactive beams Z=119 are not competitive for SHE studies yet! 1E-10 50 Ti + 249 Bk 1E-11  70 fb  Intensity of 10 9 pps corresponds to 1E-12 0.5 m g / cm 2 targets 1E-13 1E-14 1E-15 102 104 106 108 110 112 114 116 118 120 atomic number Z Courtesy Ch.E. Düllmann

Synthesis and Separation by SHIP kinematic separation in flight by velocity filter Typical yield for primary beam  6 x 10 12 / s @ Z  102 ( s  1 m b) • 1 atom/s • 1 atom/week @ Z= 112 ( s  1 pb)

Basics of Penning Trap Mass Spectrometry

Basic Idea of a Particle Trap harmonic reducing the kinetic restoring force 3D  oscillation energy by cooling    F r confine single particles (nearly) at rest • minimize perturbations (collisions, field imperfections, ...) • long observation / measurement times • Courtesy H.-J.. Kluge

Principle of Penning Traps PENNING trap • Strong homogeneous magnetic field • Weak electric 3D quadrupolar field 1 q     f c B Cyclotron frequency: q / m 2 m axial motion n z axial motion cyclotron motion n + n - trajectory magnetron motion L. S. Brown and G. Gabrielse, Rev. Mod. Phys. 58 (1986) 233 G. Gabrielse, Int. J. Mass Spectr. 279, (2009 ) 107

Cyclotron frequency measurement 60 60 Counts / bin Counts / bin B Trap 50 50 40 40 30 30 20 20 10 10 0 0 0 0 20 20 40 40 60 60 80 80 100 100 120 120 140 140 160 160 TOF / us TOF / us 1 m Drift- 100 tube 98  mean TOF / B  m 96 s F z m  94 z 92 90 Detector 88 133 Cs + 86 -4 -2 0 2 4 Excitation Frequency / Hz - 809548.8 Time-of-flight resonance technique M. König et al., Int. J. Mass Spec. Ion Process. 142 (1995) 95

Penning Trap Mass Spectrometry 1 qB determine mass via cyclotron n   C frequency measurement 2 m n Re m  n  f r m  q B 1 C ref n   ref magnetic field calibration ref 2 m ref n   q      ref  m m q m q m atomic mass n ref ref e e q ref c 1 1 n  T RF observation time s ( ) statistical uncertainty n Ntot number of det. ions T N c RF tot

Direct Mass Measurements of Nobelium and Lawrencium Isotopes with SHIPTRAP

SHIPTRAP Setup ≈ 50 MeV ≈‏1‏eV ≈‏1‏keV

SHIPTRAP Performance 60 A = 147 147 Ho + Mass resolving power of 50 m/ d m‏≈‏100,000‏ 40 147 Dy + No. of counts / bin in purification trap: 30 147 Tb + 147 Er + 20  separation of isobars 10 0 732350 732400 732450 732500 Excitation frequency / Hz 310 keV 91 Mass resolving power of 90 m/ d m‏≈‏ 1,000,000 Mean time of flight / m s 89 in measurement trap: 88 ground 87 state 1/2 + 86  separation of isomers isomeric 143 Dy 2+ state 11/2 - 85 -2 0 2 4 6 (Excitation freq. - 1505390.8) / Hz

Direct mass measurements with SHIPTRAP 206 Pb( 48 Ca,2n) 252 No 209 Bi( 48 Ca,2n) 255 Lr 207 Pb( 48 Ca,2n) 253 No 209 Bi( 48 Ca,1n) 256 Lr 208 Pb( 48 Ca,2n) 254 No 208 Pb( 48 Ca,1n) 255 No M. Block et al., Nature 463, 785 (2010), M. Dworschak et al., Phys. Rev. C 81, 064312 (2010) E. Minaya Ramirez et al., Science 337, 1183 (2012)

SHIPTRAP Results vs. Atomic Mass Evaluation

Pinning Down a -Decay Chains 270 Ds mass can be fixed with Z = 110 α 270 Ds about 40 keV uncertainty now 0.1ms Z = 108 α α 264 Hs 266 Hs 0.3ms 2.3ms Z = 106 α α 260 Sg 262 Sg 3.6ms 6.9ms α α 256 Rf 258 Rf Z = 104 6.2ms 13ms 252 No 254 No Z = 102 Anchor points 2.3s 55s