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Preparation of an isomerically pure beam and future experiments

TAS Workshop, Caen, March 30-31, 2004. Preparation of an isomerically pure beam and future experiments. Klaus Blaum for the ISOLTRAP Collaboration CERN PH-IS Geneva and GSI Darmstadt. Outline. Motivation. Experimental setup and procedure. Preparation of an isomerically pure beam.

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Preparation of an isomerically pure beam and future experiments

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  1. TAS Workshop, Caen, March 30-31, 2004 Preparation of an isomerically pure beam and future experiments Klaus Blaum for the ISOLTRAP Collaboration CERN PH-IS Geneva and GSI Darmstadt Outline Motivation Experimental setup and procedure Preparation of an isomerically pure beam Future experiments Summary

  2. Motivation: The identification puzzle in 70Cu • Problems / unknown parameters: • number of isomeric states • spin assignement • order of states • mass excess value of ground state • Requirements: • - clear state to mass assignement • high selectivity • high efficiency • ultra-high resolving power • Solution: • Combination of laser resonance • ionization, b-decay spectroscopy and • Penning trap mass spectrometry Ground and isomeric states of 70Cu JpE / keV T1/2 / s (6-) 242.4(3) 6.6(2) b–95% IT5% (3-) 101.1(3) 33(2) b–50% IT50% (1+) 0 44.5(2) b–=100% Mass excess Lit: -63202(15) keV

  3. Resonance Ionization Laser Ion Source (RILIS) 1. Surface Ionization Ion Source: No isobaric selectivity, limited applicability 2. Plasma Ion Source (ECR-Source): No isobaric selectivity 3. Resonance Ionization Laser Ion Source (RILIS): High isobaric selectivity by resonant laser ionization Limitation by surface ionized isobars

  4. Example: Cupper excitation scheme

  5. Principle of Penning Traps PENNING trap • Strong homogeneous magnetic field • Weak electric 3D quadrupole field end cap Frans Michel Penning Hans G. Dehmelt ring electrode B Cyclotron frequency: q/m

  6. 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+) The frequencies of the radial motions obey the relation Typical frequencies q = e, m = 100 u, B = 6 T f- ≈ 1 kHz f+≈ 1 MHz

  7. Excitation of Radial Ion Motions Dipolar azimuthal excitation Either of the ion's radial motions can be excitedby use of an electric dipole field in resonancewith the motion (RF excitation)  amplitude of motion increases without bounds Quadrupolar azimuthal excitation If the two radial motions are excited at theirsum frequency, they are coupled  they are continuously converted into each other Conversion of radial motions Magnetron excitation:r Cyclotron excitation:r+

  8. TOF Resonance Mass Spectrometry Time-of-flight resonance technique Scan of excitation frequency Dipolar radial excitation at f-  increase of r- Quadrupolar radial excitation near fc  coupling of radial motions, conv. 1.2 m Ejection along the magnetic field lines  radial energy converted to axial energy Time-of-flight (TOF) measurement Resolving power:

  9. TOF Cyclotron Resonance Curve (Stable Nuclide) T1/2 =  Mean time of flight / ms Excitation frequency frf / Hz TOF as a function of the excitation frequency Centroid: Determine atomic mass from frequency ratio with a well-known reference mass

  10. TOF Cyclotron Resonance Curve (Radionuclide) TOF as a function of the excitation frequency Centroid: frf Determine atomic mass from frequency ratio with a well-known reference mass

  11. Triple-Trap Mass Spectrometer ISOLTRAP 10 cm precision Penning trap 1.2 m 10 cm determination of cyclotron frequency (R = 107) B = 5.9 T preparation Penning trap stable alkali ion reference source B = 4.7 T removal of contaminant ions (R = 105) 532 nm Nd:YAG ion beam cooler and buncher cluster ion source G. Bollen, et al., NIM A 368, 675 (1996) F. Herfurth, et al., NIM A 469, 264 (2001) K. Blaum et al., EPJ A 15, 245 (2002)

  12. ISOLTRAP Setup 1 m

  13. Isomer Separation Isomerism in 68Cu: as produced by ISOLDE isolation of the 1+ ground state isolation of the 6- isomeric state • Resolving power of excitation: R≈ 107 • Population inversion of nuclear states • Preparation of an isomerically pure beam K. Blaum et al., Europhys. Lett., submitted (2004).

  14. Solving the Identification Puzzle in 70Cu Hyperfine structure of 70Cu isomers (using laser ionization):    Intensity ratio: 16% 80% 4% normalized to the area (spectrum provided by U. Köster) Isomerism in 70Cu: IpE / keV T1/2 / s (1+) 242.4(3) 6.6(2) b–95% IT5% (3-) 101.1(3) 33(2) b–50% IT50% (6-) 0 44.5(2) b–=100% Mass excess Lit: -63202(15) keV J. Van Roosbroeck et al., Phys. Rev. Lett. 92, 112501 (2004).

  15. Identification of Triple Isomerism in 70Cu  (6–) state = gs 101(3) keV Unambiguous state assignment!  (3–) state = 1.is ME of ground state is 240 keV higher than literature value! Excellent agreement with decay studies. 242(3) keV with cleaning of 6– state R  1·107  1+ state = 2.is Preparation of an isomerically pure beam!     Intensity ratio: 16% 80% 4%  normalized to the area 

  16. New Detector Setup Window (open access) Channeltron detector Spare MCP detector Feed- through Drift tube Ions from the precision trap

  17. Open Detector Geometry Principle of a CDEM DeTech Channeltron -2.5 kV -5 kV • Typical gain at 2.5 kV: ~5107 • Dark noise: ~20 mHz (measured) • Pulse width / Dead time: ~25 ns (measured) • Rinse time: ~5 ns (measured) • Detection efficiency (low energy ions): >90%

  18. Beta-Counter and Tape Station Tape station Beta-counter Tape station available at GSI! Isomerically pure ion beam (Courtesy W. Geithner)

  19. Applications • Identification of unknown contaminations • Collection of isomerically pure samples • Background-free decay studies • Background-free half-life measurements • Preliminary studies of further applications, e.g. post-acceleration with REX-ISOLDE BUT: Number of ions at present limited to about 10 ions/proton pulse. Help, advice and good ideas are welcome!

  20. Conclusion and Outlook • ISOLTRAP can perform high-precision mass measurements (< 10-8) on very short-lived nuclides (< 100 ms) that are produced with very low yields (< 100 ions/s) • ISOLTRAP can prepare isomerically pure beams and demonstrated population inversion of nuclear states • Isomerically pure beams open a new area in low-energy nuclear physics research • Setup of a tape station, decay spectroscopy and half-life measurements on an isomerically pure beam are planned within the next few years

  21. Not to Forget … Thanks to my co-workers: G. Audi, G. Bollen, D. Beck, P. Delahaye, C. Guénaut, F. Herfurth, A. Kellerbauer, H.-J. Kluge, D. Lunney, D. Rodríguez, C. Scheiden- berger, S. Schwarz, L. Schweikhard, G. Sikler, C. Weber, C. Yazidjian ..., and the ISOLTRAP and ISOLDE collaboration Thanks for the funding and support: GSI, BMBF, CERN, ISOLDE, EU networks EUROTRAPS, EXOTRAPS, and NIPNET Thanks a lot for your attention.

  22. New Detector Setup Window (open access) Feedthrough Channeltron detector Spare MCP detector Drift tube Ions from precision trap

  23. Specification of the CDEM (R-R0)/nA 1 - slope t = = 1-R0 axis section • Typical gain at 2.5 kV: ~5107 • Dark noise: ~20 mHz (measured) • Pulse width / Dead time: ~25 ns (measured) • Rinse time: ~5 ns (measured) • Detection efficiency (low energy ions): >90% Dead time measurement t: dead time R: isotope ratio nA: count rate Isotope ratio 40Ca count rate / Hz

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