Michael Dworschak, GSI for the SHIPTRAP collaboration First direct Penning trap mass measurements on transuranium elements with SHIPTRAP Michael Dworschak, GSI for the SHIPTRAP collaboration

Outline Introduction SHIPTRAP setup Direct mass measurements for Z > 100 Conclusions

Regions of interest at SHIPTRAP 82 Heavy Elements 126 proton emitters 50 N=Z, rp-process - Strong repulsive force due to large number of protons - Stability of SHE only due to shell effects - For nobelium: T(SF) > T(alpha) 82 28 20 50 8 28 20 8

Spontaneous Fission → ↑ a a E / MeV 2 E / MeV 2 (LD) B Coulomb energy 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 -150 -125 -100 -75 -50 -25 25 50 75 100 125 150 175 F.P.Heßberger 29.12.2005 Spalt1 B f net effect Coulomb energy Surface energy E / MeV a 2 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 -20 -15 -10 -5 5 10 15 20 25 d U s = shell effect at saddle point gs = shell effect at ground state B f (LD) = liquid drop fission barrier = B (LD) + (+ ) liquid drop + shell effects F.P.Heßberger 29.12.2005 spalt2 (LD) → ‚disrupting‘ force ← ‚backdriving‘ force E / MeV ↑ scission point a 2

Shell corrections in the region of heavy elements 100 120 114 162 184 108 152 N Z

Deformation in the region of heavy elements P.Möller et al. At. Data and Nucl. Data Tab. 59, 185 (1995)

The Recoil Separator SHIP velocity filter ≈ 5 MeV/u 0.1-1 MeV/u Mastertitelformat bearbeiten

The SHIPTRAP set-up to buncher SHIP beam

Principle of Penning Traps Cyclotron frequency: q/m PENNING trap Strong homogeneous magnetic field Weak electric 3D quadrupole field end cap ring electrode

Ion Motion in a Penning Trap Motion of an ion is the superposition of three characteristic harmonic motions: axial motion (frequency fz) magnetron motion (frequency f–) modified cyclotron motion (frequency f+) In an ideal Penning trap the frequencies of the radial motions obey the relation Typical frequencies q = e, m = 100 u, B = 7 T  f- ≈ 1 kHz f+ ≈ 1 MHz

TOF Resonance Mass Spectrometry Time-of-flight resonance technique Scan of excitation frequency trap drift- tube detector B Injection of ions into the trap and excitation of radius r- Excitation near fc  coupling of radial motions, conv. 1 m Ejection along the magnetic field lines  radial energy converted to axial energy Time-of-flight (TOF) measurement

TOF Resonance Mass Spectrometry Time-of-flight resonance technique trap drift- tube detector B 1 m

TOF Resonance Mass Spectrometry Time-of-flight resonance technique trap drift- tube detector B 1 m Resolving power:

Mass determination Relation between cyclotron frequency and mass due to Fluctuations of magnetic field due to temperature and pressure changes -> Calibration needed Determine atomic mass from frequency ratio with a well-known “reference mass” Normally 85Rb or 133Cs are chosen as reference masses

SHIPTRAP Performance Mass resolving power of m/dm ≈ 100,000 in purification trap:  separation of isobars ground state 1/2+ isomeric state 11/2- Mass resolving power of m/dm ≈ 1,000,000 in measurement trap:  separation of isomers

Direct Mass Measurements above Z = 100 Requirements: energy matching of reaction products to trap's energy scale high efficiency to deal with very low production rates 1 atom/s @ Z=102 (s  mb) 1 atom/week @ Z=112 (s  pb) high cleanliness for low background stable and reliable operation over extended time

Production of nobelium isotopes Fusion-evaporation 4.5MeV/u about 1013 particles / s 200 keV/u about 1 particle / s

Production of nobelium isotopes Fusion probability increasing with beam energy Survival probability of compound nucleus decreasing with beam energy 208Pb(48Ca,1-3n)253-255No

Direct Mass Measurements of 252-254No 100 120 114 162 184 108 152 N Z

Direct Mass Measurements of 252-254No August 2008: 206-208Pb(48Ca,2n)252-254No doubly-charged nobelium ions extracted low production rates: -> about 4 h for each resonance 133Cs used as reference mass (same q/m ratio) Production rate Half-life Half-life of isomer resonances 252No 0.4 atoms / s 2.44(4) s 110(10) ms 3 253No 1 atom / s 1.62(15) min < 1 ms 5 254No 2 atoms / s 51(10) s 266(2) ms 4

Direct Mass Measurements of 252-254No Results in agreement with previous AME values ME uncertainties in the order of 10-30 keV First direct mass measurements in the region Z > 100

Principle of mass determination with a decay energies

Definitions in the Atomic Mass Evaluation Primary data: determined by at least two independent measurements Secondary data: determined by only one measurement

Combining the results from a decays and Penning trap Difficulties: decays not between ground states "broken" a-chains energy summing with conversion electrons

Combining the results from a decays and Penning trap Difficulties: decays not between ground states "broken" a-chains energy summing with conversion electrons

Combining the results from a decays and Penning trap

Link to island of stability Combine new, directly measured masses and a-decay spectroscopy Determine the masses of short-lived higher-Z nuclides To be determined: a-decay of 262Sg (15%)

Direct Mass Measurements of 255Lr Extend direct mass measurements to higher Z 252No 253No 254No Rf, Sg,... 255Lr 103 255Lr+ April 2009: 209Bi(48Ca,2n)255Lr rate of incoming particles for 255Lr only 0.3 ions/s singly and doubly-charged ions extracted 255Lr nuclide with lowest rate ever measured in a Penning trap

The Route to SHE increase sensitivity and efficiency (non-destructive) detection system with single-ion sensitivity new cryogenic gas cell improve primary beam access to more neutron-rich nuclides hot-fusion reactions with actinide targets connection to gas-filled separator TASCA

Summary and Outlook First direct mass measurements of nobelium isotopes have been performed with SHIPTRAP Using results from direct mass measurements more primary nuclides could be obtained Nobelium isotopes linked to superheavy elements by a-decay chains Next step: go to higher-Z nuclides In the long-term future: Penning traps can contribute to identify long-lived SHE

SHIPTRAP Collaborators M. Dworschak, D. Ackermann, K. Blaum, M. Block, C. Droese, 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 Thank you for your attention !

Penning trap basics B Axial motion: oscillation in E-field z 0 Ф0 B Magnetron motion: E x B drift Axial motion: oscillation in E-field Reduced cyclotron motion: Relevant for mass measurements:

Cyclotron frequency measurement off res. m ~ r w on res. trap drift- tube detector B Michael Block DPG-Frühjahrstagung, München 2006

Super Heavy Elements Z N GSI elements Z = 107-112 100 120 114 162 184 108 152 N Z GSI elements Z = 107-112 112 Rg Ds Mt Hs Bh how heavy can the elements be? location of the island of stability? structure of SHE? stability due to shell effects  accurate binding energies needed 252-254No

TOF Cyclotron Resonance Curve TOF as a function of the excitation frequency off res. on res. Resolving power: Determine atomic mass from frequency ratio with a well-known “reference mass”.