Trap assisted decay spectroscopy setup at ISOLTRAP

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1 Trap assisted decay spectroscopy setup at ISOLTRAP Motivation Penning traps: masses and isobaric selectivity ISOLTRAP mass spectrometer at ISOLDE/CERN Decay spectroscopy at ISOLTRAP: setup and 1 st run Conclusions and outlook Magdalena Kowalska MPIK Heidelberg On behalf of the ISOLTRAP collaboration

2 Motivation Perform mass and decay studies on isomerically and/or isobarically pure beams, by use of Penning traps Possible applications: Penning traps used as purifiers: for decay studies hampered by isobaric and isomeric contamination Decay spectroscopy used to assist mass measurements and distinguish between different species First attempt for trap assisted decay studies performed at REX ISOLDE: Nucl. Instr. and Meth. A 492 (2002) Since then, used regularly at JYFLTRAP: e.g. Eur. Phys. J. A 31, 1 (2007)

3 Isobaric cleaning in a Penning trap Trap filled with He buffer gas around 1e 4 mbar 4 mm diaphragm in the upper endcap electrode 1. Inject ions Wanted (e.g82zn) Unwanted (e.g. 82Ga) 2. Excite ions with dipolar excit. at. is mass independent, so all ions will be excited. 3. Use quadrupolar excit. at c ( 82 Zn) (mass dependent): only wanted ions can get cyclotron motion. 4. Eject ions. Only wanted ions can go out. By gas friction, they lose energy and are centered. Achievable mass resolution: up to m/dm=10e5 (1 MeV around A=100)

4 ISOLTRAP spectrometer at ISOLDE CERN tape station Decay studies ToF detector MCP 3 / channeltron Mass determination Precison Penning trap B = 6T MCP 2 Isobaric cleaning Preparation Penning trap B = 4.7T reference ion source MCP 1 RFQ cooler and buncher ISOLDE 60 kev ion beam HV platform Carbon cluster ion source

5 Decay system: Challenges at ISOLTRAP Measurements: Masses: with ToF method on an ion detector behind the precision trap Decay studies: implantation into a tape placed behind the movable ion detector Compact aluminium decay chamber: copy of Bordeaux group Challenges: Keeping mbar vacuum in the massmeasurement part Height limitation due to ISOLDE crane Reacceleration of ions for efficient tape implantation Ion transport and beta detection in magnetic field Compact tape system: small GSI tape station Simion simulations and mu metal shielding Pulsed electrode: 1kV to +30kV (7 cm long)

6 Decay system: Challenges The ISOLDE crane makes trouble

7 Light guide tape Decay system mcp scintillator electrode collimator electrode Pulsed electrode channeltron mcp Penning turbo Side view

8 Decay system Plastic scintillator tube Light guide Top view PTM2 Ge2 PTM1 Ge1 Yellow: air pressure Implantation point Blue: 1e 6 mbar vacuum

9 Detection chamber Thin (2mm) organic scintillator Lightguide Tape holder photomultipliers ions Thin (0.5mm) Al walls

10 September 2009: 2 short runs System commissioning 80Rb: cyclotron resonances and beta and gamma spectra High yield Relatively short lived Decays to stable 80Kr Possible contamination with 80Sr Tests of: Vacuum conditions Ion reacceleration and implantation depth Ion transport efficiency and detection efficiency Implantation accuracy Two decay DAQ configurations used: Complete DAQ: beta gamma, gamma gamma coincidence Mass assisting mode: one Ge detector and a plug in MCA, beta detection by MCA, no coincidence

11 System commissioning Pressure: Around the trap doesn t change at all In the detection chamber goes back to 1e 8 mbar within a few minutes after closing the valve + Almost simultaneous decay and mass studies possible Ion reacceleration and implantation depth: With pulsed electrode on: change in ion ToF visible, ions go through potential barier Half life correct (no ion losses after implantation) + Implantation depth is fine

12 System commissioning Ion transport efficiency: ISOLDE yield: T. Stora: 2e7 ions/uc; our rough estimate 5 10e7 ions/proton pulse Multichannel plate (MCP5) behind precision trap: 5e3 ions/1ms (=>5e6 ions/s; 10%) MCP in front of scintillator with 1 collimator: 50% of MCP5, with two collimators: 10% An order of magnitude loss between the trap and implantation point: to be regained Beta and gamma detection efficiency: beta: 50% efficiency verified with 90Sr source gamma: 0.5% absolute efficiency per detector with gamma sources 60Co, 137Cs, 207Bi + beta efficiency fine; gamma efficiency fine (to be verified with Geant4 simulations) Implantation accuracy: measure activity after moving the tape: 50% of the beam still visible ( tape transport very reliable and reproducible) Ion beam and tape not well aligned; better control of focus/position or wider tape needed

13 System commissioning Counts 80Rb kev line Energy (kev)

14 System commissioning Counts Beta energy spectrum Energy (kev)

15 Summary and outlook Penning traps can provide isobarically and even isomerically pure beams => decay studies on pure beams and beam composition investigations are possible Decay spectroscopy system at ISOLTRAP faces several technical challenges: The system has been tested online in autumn 2009: + Fine: vacuum, implantation depth, beta and gamma detection efficiency To improve: transmission, implantation position To test: verify cleaning efficiency for a high number of ions in the trap Outlook: Offline work on the points to be improved and tested GEANT4 simulations of the detection chamber Assist regular mass measurements at ISOLTRAP Decay studies of neutron rich Tl (and/or Hg) isotopes

16 Thanks to my collaborators: S. Naimi, J. Stanja, J. Agramunt, A. Algora, D. Beck, B. Blank, K. Blaum, Ch. Boehm, Ch. Borgmann, M. Breitenfeldt, E. Estevez, D. Fink, L.M. Fraile, S. George, F. Herfurth, A. Herlert, H.-J. Kluge, S. Kreim, D. Lunney, D. Neidherr, K. Riisager, M. Rosenbusch, B. Rubio, S. Schwarz, L. Schweikhard, K. Zuber TU Dresden Thanks for your attention