Perspectives for Penning Trap Mass Measurements of Super Heavy Elements Michael Block GSI Workshop on Rare Atoms Ann Arbor 2009 Introduction to Super Heavy Elements Production of SHE Mass determination of SHE Direct mass measurements for Z > 100 with SHIPTRAP Extending the reach towards SHE Conclusions
Mass Measurements for Nuclear Physics Isospin Symmetry Pairing Exotic decays Fundamental Interactions Stability of SHE Proton Number Z rp-process r-process Magic Numbers Evolution of Shell Structure Halos and Skins Neutron Number N
Extending the Nuclear Chart at RIB Facilities
Extending the Nuclear Chart at RIB Facilities nuclei total: 2974 in nature: 286 3000 known nuclides isomers
Super Heavy Elements 120 108 100 Z 114 GSI elements Z = 107-112 Hs Bh Mt 252-254 No 152 Ds 112 Rg 270 Hs 162 283 112 how heavy can the elements be? location of the island of stability? structure of SHE? 184 stability due to shell effects accurate binding energies needed N
Production of SHE Exclusive access to nuclides with Z > 100 by fusion-evaporation reactions cold fusion: heavy ions on Pb and Bi targets hot fusion: 48 Ca induced reactions on Actinide targets Heavy-ion accelerator to provide high-intensity stable beams at coulomb barrier energies thin targets 0.5 mg/cm 2 Recoil separator to separate evaporation residues from primary beam in flight
GSI: Unique Combination for SHE Studies ECR + UNILAC Stable targets SHIP SHIPTRAP Beam Actinide targets TASCA TASISpec Courtesy of Ch. E. Duellmann Chemistry Radiochem. labs Chemical theory
Rc 1505; 2f18 The UNIversal Linear ACcelerator UNILAC 12 MeV/u for all elements Beam intensity (on target) 0.5-4 µa p (25% duty cycle)
The Recoil Separator SHIP 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: 3 25 µs 0.1-1 MeV/u Mastertitelformat bearbeiten velocity filter 5 MeV/u
TASCA - a Gas-filled Separator for Chemistry and Physics TASCA TransActinide Separator and Chemistry Apparatus C 5 H 5 Chemical investigations of the transactinide elements: one-atom-at-a-time chemistry Nuclear structure investigations Hot-fusion nuclear reaction studies Courtesy of Ch. E. Duellmann
TASCA Gas-filled Separator
GSI: Elements 107 112 48 Ca + X Sr proton number X + 208 Pb, 209 Bi X X Kr Se Ge Zn Ni Fe Cr Cf Cm Am Pu Np U Ti Ca X X neutron number Courtesy of S. Hofmann
Results at FLNR Dubna 48 Ca + X Sr Protonenzahl X + 208 Pb, 209 Bi Kr Se Ge Zn Ni Fe Cr Cf Cm Am Pu Np U 85 chains 34 isotopes 5 new elements Ti Ca X X Neutronenzahl Courtesy of S. Hofmann
Key Results: growing T 1/2 and constant σ T 1/2 = 1 ms 10 s σ = 0.5 5 pb Courtesy of S. Hofmann
Producing New Isotopes and Elements 54 Cr + 248 Cm => 302 120* σ = 30 fb 0.6 pb for BF = 7.0 8.3 MeV Experiments with 248 Cm targets CN Fe Mn Cr V Ti Sc Ca K Ar Cl S P Si Al Mg Na Ne F O Courtesy of S. Hofmann
Knowledge of Masses for Z > 100 AME 2003 Fm (Z =100) no direct mass measurements for Z>92 some masses indirectly determined from Q α values many masses extrapolated from systematic trends
Impact of Masses for Z > 100 AME 2003 Fm (Z =100) binding energy determines existence of SHE studies of the shell structure evolution N = 152, 162 pin down endpoints of decay chains (Rf, Sg) studies of long-lived isomeric states
Mass Determination using Decay-links α 270 Ds (Z=110) 266 Hs 262 Sg 258 Rf Difficulties: "incomplete" α-chains decays not between ground states uncertainties accumulate 254 No 250 Fm 246 Cf 242 Cm 238 Pu F.P. Hessberger et al., Eur. Phys. J. A 22, 417 (2004)
Direct Mass Measurements above Z = 100 Typical production rates at present facilities: 1 atom/s @ Z=102 (σ µb) 1 atom/week @ Z=112 (σ pb) Present reach of Penning Traps for RIBs Half-life Rate of trapped ions > 10 ms > 0.01 / s Requirements: energy matching of reaction products to trap's energy scale high efficiency to deal with very low production rates high cleanliness for low background stable and reliable operation over extended time
Penning Trap Basics in Brief Ф 0 z 0 r 0 B axial motion magnetron motion cyclotron motion Axial motion: harmonic oscillation in E-field ω = qv0 z 2 md Magnetron motion: E x B drift ωc ω = 2 ω 2 c 4 2 z ω 2 in an ideal trap: ω c = ω + + ω = q m B Reduced cyclotron motion: ωc ω+ = + 2 ω 2 c 4 2 z ω 2 invariance theorem: 2 2 2 2 c = ω+ + ω ω z ω + L. S. Brown and G. Gabrielse, Rev. Mod. Phys. 58 (1986) 233 G. Gabrielse, IJMS 279, (2009 ) 107
Cyclotron frequency measurement Step1: Excite radial motion Step 2: Convert E rad into E axial, measure TOF B Inhomogeneous part of magnetic field z Detector Record TOF as function of excit. frequency Resonance U RF 1 0 0 E - ~1meV E + ~ 1eV 60 50 mean TOF /µs 9 8 9 6 9 4 9 2 9 0 It s time for experiment counts 40 30 20 10 8 8 8 6 f c - 4-2 0 2 4 E x c ita tio n F r e q u e n c y / H z - 8 0 9 5 4 8.8 0 0 20 40 60 80 100 120 140 160 TOF / us M. König et al., Int. J. of Mass Spectr. and Ion Proc. 142 (1995) 95 G. Bollen et al. J. Appl. Phys. 68 (1990) 4355; G. Gabrielse, Phys. Rev. Lett 102, (2009) 172501;
Gas Cell Buncher Transfer Penning Traps SHIP ion beam Entrance window Extraction RFQ SHIPTRAP Setup 0.1-1 MeV/u 1 ev Cooler and Buncher RFQ Laser or surface ionization source Quadrupole deflector Superconducting magnet Diaphragm MCPdetector DC cage RF funnel Purification trap Measurement trap
SHIPTRAP Performance 60 50 147 Ho + A = 147 Mass resolving power of No. of counts / bin 40 30 20 147 Er + 147 Dy + 147 Tb + m/δm 100,000 in purification trap: 10 separation of isobars 0 732350 732400 732450 732500 E xcitation frequency / H z Mean time of flight / µs 91 90 89 88 87 86 85 310 kev isomeric state 11/2 - ground state 1/2 + -2 0 2 4 6 (Excitation freq. - 1505390.8) / Hz 143 Dy 2+ Mass resolving power of m/δm 1,000,000 in measurement trap: separation of isomers
Direct Mass Measurements of 252-254 No 120 Z 114 108 Gateway to Superheavies 252-254 No 184 100 152 162 N
Entering the Gateway to the SHE Mean time of flight / µs 92 90 88 86 84 82 80 78 76 74 72 253 No 2+ -3-2 -1 0 1 2 3 Excitation frequency / Hz - 850012 April 09 255 Lr 103 252 No 253 No 254 No Aug 08 Rf, Sg,... rate of incoming particles for 255 Lr only 0.3 ions/s First direct mass measurements in the region Z > 100 255 Lr nuclide with lowest rate ever measured in a Penning trap M-M SHIPTRAP / kev 50 0-50 -100-150 -200-250 252 No 253 No SHIPTRAP AME'03 254 No
Mass determination of SHE Combine new, directly measured masses and α-decay spectroscopy Determine the masses of short-lived higher-z nuclides To be determined: α-decay of 262 Sg (15%)
The Route to SHE improve production rates increase primary beam intensities improved ECR sources (28 GHz) optimized cw accelerator for stable beams target developments (compounds, cooling) access to more neutron-rich nuclides hot-fusion reactions with actinide targets higher sensitivity and efficiency detection system with single-ion sensitivity next generation gas stoppers
Higher Intensities at GSI New 28-GHz EZR Source: Higher charge state Higher intensity Factor: 2 5 New RFQ Injector: Duty factor 25 % => 50 % Higher injection energy Higher acceptance Factor: 2 intensity (eµa) 1000 28 GHz SC-ECRIS (extrapolated) 28 GHz SERSE 18 GHz SERSE 18 GHz RT-ECRIS 14 GHz GSI-CAPRICE II 100 10 1 20 25 30 35 40 45 50 Xe charge state U. Ratzinger, K. Tinschert et al.
Optimized Accelerator for SHE Production Superconducting continuous wave accelerator: RFQ, 108 MHz IH DTL, 108 MHz CH DTL, supercond. QWR Cavities 324 MHz 108 MHz Debuncher Energy MeV/u room temperature super conducting super conducting 0.003 0.3 1.4 1.8 2.4 3.3 4.2 5.2 6.1 7.1 ECR source 0 5 10 15 20 25 30 Z / m U. Ratzinger et al., Frankfurt University W. Barth, L. Dahl et al., GSI Design Design specifications DC DC beam beam 1 < A/q A/q < 7 E beam : beam : 4-7.5 4-7.5 MeV/u MeV/u E E beam < beam ±3keV/u
The Route to SHE increase sensitivity and efficiency (non-destructive) detection system with single-ion sensitivity mass measurement with one ion only next generation gas stoppers: cryogenic for highest cleanliness RF carpet extraction systems
Coupling of TASCA and SHIPTRAP C-Aerosol Gas-jet Skimmer + Ion source RFQ Buncher M. Schaedel Ch. E Duellmann F. Herfurth K. Eberhardt K. Blaum C. Smorra M. Eibach SHIPTRAP D Q 1 Q 2 TASCA RTC
Conclusions Direct mass measurements for No, Lr region have been performed High-precision mass measurements of stopped rare isotopes with production rates of about 0.1 per second are possible today Opened the door for novel experiments with stopped heavy elements Technical developments and new techniques will pave the way to heavier elements Thank you for your attention!
THANKS TO The SHIPTRAP, TRIGA-TRAP, and TASCA Collaborations D. Ackermann, K. Blaum, C. Droese, M. Dworschak, S. Eliseev, E. Haettner, F. Herfurth, F. P. Heßberger, S. Hofmann, J. Ketter, J. Ketelaer, H.-J. Kluge, G. Marx, M. Mazzocco, Yu. Novikov, W. R. Plaß, A. Popeko, D. Rodríguez, C. Scheidenberger, L. Schweikhard, P. Thirolf, G. Vorobjev, C. Weber, K. Eberhardt, Ch.E. Duellmann, and M. Schädel