In-Gas Laser Ionization and Spectroscopy experiments at S 3 -GANIL

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1 In-Gas Laser Ionization and Spectroscopy experiments at S 3 -GANIL R. Ferrer, L. Ghys, M. Huyse, Yu. Kudryavtsev, D. Pauwels, D. Radulov, L. Rens, P. Van den Bergh, C. Van Beveren, and P. Van Duppen Instituut voor Kern- en Stralingsfysika, KU Leuven (Belgium) Low-Energy Radioactive Isotope Beam Production by In-Gas Laser Ionization for Decay Spectroscopy at RIKEN December 10-11, 2012 RIKEN-Wako OUTLINE Motivation In-Gas-Cell Laser LISOL Progress on the implementation of In-Gas-Jet Laser Spectroscopy Summary and Outlook

2 MOTIVATION Strategic areas of chart of nuclides understand nuclear structure effects N = Z nuclei - Study role of proton-neutron correlations - Proton drip line - rp process, nuclei far off stability - Proximity doubly magic N = Z = 50 - strong shell correction effects - SHE - understanding of SHE and those at the limit of nuclear existence - DAY S3 In Gas Laser Ionization and Spectroscopy experiments of: 94 Ag High-spin isomerism, β-delayed p, 1- and 2-p emission 80 Zr (spk. person: B. Bastin) Single particle behavior and effective interactions Sn Test validity of shell-model predictions VHE (Z ~ ) Validate nuclear and atomic theory

3 S SPIRAL2 Very high intensity primary beams Full range of primary beams (H to U) High primary beam rejection High acceptance spectrometer

4 LISOL Beams since 1994 Heavy Ion-induced fusion evaporation reactions: Rh,Ru,Ti,Sn,In,Ag,Ac EPJ A 21 (2004)243 Light Ion-induced fusion evaporation reactions: Co,Ni,Mn,Cr,V,Cu PRC 59 (1999) 2416 PRL 103 (2009) PRC 81 (2010) Stopping of 185 MeV stable Ni beam Characterization of gas cell NIM B 187 (2002) 535; NIM B 226 (2004) 401 Sp. fission of 252 Cf: Rh,Ru,Mo,Pd NIM B 266 (2008) 4368 Proton-induced fission of 238 U: Fe,Co,Ni,Cu PRL 81 (1998) 03100, PRC 64 (2001) PRC 74 (2006) , PRC 78 (2008) (R) PRC 79 (2009) , PRC 79 (2009) Implementation of Dual Chamber gas cell improves ionization efficiency and selectivity In-source laser spectroscopy at LISOL Yu. Kudryavtev et al., NIM B 267 (2009) 2908

5 Dual Chamber Gas Cell Laser beams Longitudinal Ar/He from gas purifier 500 mbar Separation of stopping and laser ionization volumes improves: Laser ionization efficiency for high cyclotron beam current Beam from Cyclotron Stopping chamber Ø 4 cm Ion selectivity Laser Ionization chamber Ø 1 cm Ion collector Ionization chamber Ion Collector Filament Production of 94 Rh Selectivity: [Laser(on)/Laser(off)] Ion Collector OFF = 450 Ion Collector ON = 2200 Laser beams Transverse SPIG Exit hole Ø mm In-gas-cell spectroscopy of neutron deficient Cu isotopes T. E. Cocolios et al., PRL 103, (2009) T. E. Cocolios et al., PRC 81, (2010)

6 In-Gas-Cell Laser Spectroscopy of Ag N=50 92 Mo( 14 N 130 MeV,2pxn) 104 x Ag 64,nat Zn( 36 Ar 125 MeV,pxn) Ag β counts Ag 99 Ag 101 Ag ν GHz Derived experimental proton g-factors Open circle calculated value assuming I=7/2+ U. Dinger et al., Nucl. Phys. A 503 (1989) 331 R.F. Phys. Lett. B (in preparation)

7 Attempt at Laser Spectroscopy of Sn 92 Mo( 16 O-100 MeV,2-3n) 105,106 Sn continuum Aut. state IP cm -1 Strong ν-dependence on gas cell pressure 1 P 1 λ 2 =454.9 nm cm -1 Not possible HFS measurements (FWHM~15GHz) λ 1 =254.7 nm 3 P 0 Current on SEM (na) argon 100 mbar 140 mbar mbar 280 mbar 400 mbar λ mbar 0.8 λ RC Sn 120 Sn Current on SEM (na) argon 500 mbar 390 mbar 300 mbar 200 mbar 150 mbar 100 mbar RC Wavelength (cm -1 ) Shift = -4.0(0.3) MHz/mbar Broadening=32(4) MHz/mbar Wavenumber (cm -1 ) Shift = -150(10) MHz/mbar Broadening=210(25) MHz/mbar

8 Broadband Spectroscopy on Ac cm cm -1 g.s. 212 Ac continuum Ac nm I.P cm -1 4 P 5/ nm 2 D 3/2 Counts on SEM (arb. u.) Alpha counts in 300 s FWHM= 24 GHz FULL POWER FWHM= 86 GHz POWER ATTEN. FWHM= 32 GHz 197 Au( 20 Ne-145 MeV,4-5n) 212,213 Ac Cross section 2.3 mb for 212,213 Ac A. Andreyev et al. Nucl. Phys. A 568 (1994) ST Step 2 nd Step Ref Ac 227 Ac Gas FWHM= 81 GHz FULL POWER FWHM= 170 GHz Ref. Gas 212 Ac 212 Ac Wavenumbers (cm -1 ) Wavenumbers (cm -1 )

9 In-Gas-Jet Laser Spectroscopy Increase Resolution - Ionization in cold jet expanding out of the gas cell and Selectivity - Ionization in LIST mode K. Blaum et al., NIM B204 (2003) 331 Demonstrated proof of LISOL T. Sonoda et al. NIM B267 (2009) 2918 Ref. Cell 58 Ni FWHM= ~ 2 GHz Gas cell Ar 500 mbar FWHM=6.5 GHz Gas jet FWHM= ~ 2 GHz Requirements to obtain maximum benefits: - Improve spatial overlap and temporal overlap Wavenumber [cm -1 ] - Reduce laser bandwidth

10 Lasers propagating direction Improving Spatial Overlap RFQ Ion Guides (IG s) 90 o -bent RFQ r 0 = R rod = 6 mm L seg. = 9 mm r 0 R rod Extraction RFQ r 0 = R rod = 2 mm L seg. = 4 mm M. Reponen et al., NIM A 635 (2011) o -bent RFQ pumping barrier Acceleration region Lasers counterpropagating Extraction RFQ

11 Commissioning of the RFQ IG s Gas Cell 90 o bent RFQ Laser beams Extraction RFQ 10-3 mbar 10-6 mbar Extraction Electrode

12 Transmission through RFQ IG s Comparison experiment vs. simulation (bkg p = 1e-3 mbar) Trans. (%) RF1 = 350 Vpp SimIon Exp RF2 (Vpp) Copper filament: A/Q= 63, 65, 81, 83, 99, Performance of ion guides found to be in agreement with expectation - Transmission efficiency ε= 80% - Similar transmission found for bkg p=0.1 mbar

13 Selection of Ions from the Gas Jet Determine the blocking potential - Time profiles with lasers in counterpropagating direction DC1= 10V DC1= 20V DC1= 30V DC1= 40V A/Q= 63 DC2= -10 V 1*10-1 mbar Counts on SEM DC1 DC t (ms) Bias voltage of 40 V block all ions from gas cell

14 Sideband Formation A/Q= 81 [ 63 Cu H 2 O] + DC2= -10 V 1*10-1 mbar DC1=0 V DC1=10V DC1=20 V DC1=30 V DC1=35 V Counts on SEM DC1 DC t (ms) Molecule formation occurs in the GC (short mfp) and not in the gas jet (long mfp)

15 Effect of dc gradient on the Ion Beam - Time profiles with lasers in counterpropagating direction A/Q= 63 DC1= 40 V 1*10-1 mbar Counts on SEM (arb. u) t (ms) DC2= 0 V DC2= -1 V DC2= -2 V DC2= -5 V DC2=-10 V DC2=-20 V DC2=-40 V DC2=-50 V DC2=-60 V Arrival time (ms) FWHM (ms) DC2 (V) 10-3 mbar 10-1 mbar 10-3 mbar 10-1 mbar Manipulation of ions by dc gradient DC2 (V)

16 Improving Time Overlap Test of a high pulse repetition rate laser system (Uni-Mainz, GANIL, JYFL, RIKEN, IPNO, JINR) - Performance comparison between high repetition Ti:sa lasers and LISOL dye lasers - Comparable results for in-gas-cell ionization Ref. Cell β - counts in 100 s Cu Rep. Rate (Hz) Ti:sa lasers Dye lasers Ion Signal (arb. u.) Gas Cell Ar 200 mbar SPIG (gas jet) -Resolution of HFS of stable 63 Cu in the gas jet mainly limited by laser bandwidth ν (THz) R. F., V. Sonnenschein et al., NIM B 291 (2012) 29

17 Reduction of the Laser Bandwidth Study of typical LISOL narrow-band pulse using FP interferometer - Radial profile of interference ring shows four oscillation modes - Separation between modes is 400 MHz mode FWHM= 150MHz Laser bandwidth ~1.4 GHz (SHG) 1. Implementation of a thicker etalon (14 mm air spaced) allows selection of a single mode 450 MHz FWHM (Doppler broad.) 2. Amplification of CW Single Mode Diode Laser in Pulsed Dye Amplifier Tunable cw Diode Laser (Toptica) nm Dye Amplifier Amp. I Amp. II SHG nm Towards Ref. Cell Excimer XeCl Laser KDP

18 High energy HFS components of the 327 nm line in 63,65 Cu 1.6 C D+C D Ref. Cell 1.4 Signal on SEM (arb. u) Cu 63,65 Cu 150 MHz 65 Cu Wavenumber (cm -1 ) Estimated 90 MHz Fourier-limited (5ns) laser bandwidth is affected by residual Doppler broadening resulting in a signal line width of 150 MHz

19 KU Leuven

20 Laser equipment for HELIOS Two step laser ionization spectroscopy in the gas cell Two high-repetition-high-power Nd:YAG pump Laser - Max. average power = 100 W (@ 532 nm) 40 W (@ 355 nm) - Max. repetition rate = 15 khz Two high repetiton rate dye lasers - Tunable wavelength from 215 to 900 nm - Linewidth ~ 0.07 cm -1 ( 2 GHz) Nd:YAG Laser Dye Laser For high resolution spectroscopy in the gas jet first step will consist of A continous wave (CW) single mode tunable diode laser - Linewidth = 1 MHz - Typical (mode-hop free) tuning range ~ 20 nm Suitable for only one element (requires change of diode depending on adopted ionization scheme ) Diode Laser A pulsed dye amplifier with second harmonic generator

21 IGLIS S 3 94 Ag - Atomic scheme known - In-jet mode to increase resolution gas Ion Beam from S 3 Gas Cell de Laval nozzle Gas jet Gas cell chamber S-shaped RFQ 1-D laser beam expander Diff. pumping chamber Extraction RFQ Extraction chamber Towards mass separator Thin entrance window λ 1 λ 2 λ 2 λ 1 In-gas-cell In-gas-jet ionization ionization mbar VHE (actinides) - Atomic scheme known for Ac - Develop Atomic schemes for other actinides - In-gas cell/in-gas jet spectroscopy mbar 80 Zr - Atomic scheme unknown - In-gas cell/in-gas jet spectroscopy < mbar Sn - Atomic scheme known -In-gas-jet spectroscopy required owing to p dependence

22 Summary & Outlook In-gas-cell laser spectroscopy of Cu and Ag performed at LISOL Similar results are being pursued for the Ac isotopes In-gas-jet laser spectroscopy will allow higher resolution & selectivity More isotopes will be accessible First LISOL Bent RFQ + Narrow band laser + free jet (de Laval Nozzle) RFQ IG s commissioned and tested Performance according to expectations Start construction of HELIOS KU Leuven Commission new (high repetition) laser system Study gas jet formation and test new gas cell design Optimize high-resolution laser spectroscopy in the gas jet (see talk Yuri) Apply technique on radioactive S 3

23 Acknowledgments LISOL team: R.F, L. Ghys, M. Huyse, Yu. Kudryavtsev, D. Pauwels, D. Radulov, L. Rens, P. Van den Bergh, C. Van Beveren, and P. Van Duppen LISOL Alumni: T. Cocolios, I.G. Darby, T. Sonoda Collaborators: University of Mainz A. Hakimi, T. Kron, S. Raeder, S. Richter, J. Rossnagel, K. Wendt GANIL-SPIRAL2- IPN Orsay B. Bastin, S. Franchoo, N. Lecesne, F. Lutton, B. Osmond, J. Piot, H. Savajols, J. C. Thomas JYFL University of Jyväskylä I. Moore, M. Reponen, V. Sonnenschein RIKEN T. Sonoda JINR-Dubna S. Zemlyanoy R. Ferrer Workshop on Gas-Cell based Laser Spectroscopy Developments