In-gas cell laser spectroscopy of neutron-deficient silver isotopes

Transcription

1 In-gas cell laser spectroscopy of neutron-deficient silver isotopes A.N. Andreyev, B. Bastin, N. Bree, J. Büscher, T.E. Cocolios, I. Darby, J. Elseviers, R. Ferrer, J. Gentens, M. Huyse, Yu. Kudryavtsev, D. Pauwels, T. Sonoda, P. Van den Bergh and P. Van Duppen Instituut voor Kern- en Stralingsfysica, K.U.Leuven, Belgium CERN-ISOLDE, Switzerland Laser resonant ionization in a gas cell: the LISOL facility Basic principles and recent developments Laser spectroscopy on-line studies Cu Ag : along the N=Z line Possible improvements and further developments: In, Sn, Actinides New opportunities for gas-cell based laser spectroscopy Gas cell coupled to S3-SPRIAL (GANIL) separator Conclusion and outlook for EURISOL

2 Laser Spectroscopy of Radioactive Isotopes Model independent information on: (provided the atomic physics is understood) Charge radii Magnetic dipole - electrical quadrupole moments Spins Comparison with nuclear theory Limited information: Refractory type elements (B. Cheal,- PRL102 (2009) ) Actinides and trans-actinides Laser spectroscopy studies at LISOL (H. Backe,- PRL 80 (1998) 920, M. Sewtz,- PRL 90 (2003) ) W. Nörtershäuser et al.,

3 Louvain-la-Neuve Radioactive Beam Facility CYCLONE110 cyclotron p,d,α and heavy ions Radioactive Ion Beams M. Huyse, R. Raabe J. Phys. G 38 (2011) Detection Laser ion source Laser System LISOL - Leuven Isotope Separator On-Line

4 LISOL Laser Ion Source Toward mass separator Exit hole Sextupole Ion Guide (SPIG) Target Reasonable efficiency % Selective ionization: laser on/off p-induced fission reactions h.i fusion evaporation reactions Refractory elements (buffer gas cell) Short delay times: ms Cyclotron beam He/Ar 500 mbar Ar/He from gas purifier Filament Laser beams Thermalization in a buffer gas cell (500 mbar Ar/He) Neutralization (>99%) Resonant laser ionization: Z-selection Extraction by gas flow, transport by RF ion guide Mass separation: A/Q selection [M. Facina,- NIMB 226 (2004) 401] [Y. Kudryavtsev,- NIMB 204 (2003) 336]

5 Laser system Excimer lasers Dye lasers SHG Reference cell Yu.Kudryavtsev, SMI06, March 27-28, 2006 Towards LIS Yu.Kudryavtsev, LAP2010, Sep.27-Oct.1, 2010

6 9/44 Front end of the LISOL mass separator Cyclotron beam Extraction electrode SPIG Gas Cell Gas from purifier

7 Two-step laser ionization schemes used at LISOL 80% of all elements can in principle be ionized by the LISOL laser system Tunable range used on-line nm used off-line

8 Nuclear Structure around 56 Ni (Z=N=28) 57 Cu 199 ms πp3/2 N=28 N=40 Magnetic moment Cu 55 Ni 209 ms 56 Ni 6.0 d 55 Co 17 h 54 Co N=28 57 Ni 36 h 58 Ni Z=28 Magnetic moment [µ N ]? µ Schmidt (p 3/2 ) = +3,79 µ N Minaminoso Experiments Golovko Honma Mass Number Magnetic moment of 57 Cu isotopes using the β-nmr technique..imply significant shell breaking at 56 Ni with N=28. [Minamisono,- PRL 96 (2006) ] In source laser spectroscopy at ISOLDE down to 58,59 Cu [Stone,- PRC 77 (2008) ] Co-linear laser spectroscopy: 58,75 Cu [Vingerhoets PRC 82 (2010) , Flanagan PRL 103 (2009) ]

9 In-gas-cell laser spectroscopy of 57,59 Cu Production p and 3He induced reactions (~2 µa) 58 Ni( 3 He, pn) 59 Cu 58 Ni(p, 2n) 57 Mass separator Cu (T 1/2 =199 ms) 60 Ni(p, 2n) 59 Cu Argon buffer gas at 130 mbar Lasers repetition rate at 200 Hz Laser spectroscopy - resonant ionization reference cell ( 63,65 Cu evaporated) beam intensity after mass separation: stable 63,65 Cu: MCP radioactive mass 57,59 Cu: β-detection Simultaneous measurement in the reference cell and 57 Cu/ 63 Cu or 59 Cu/ 65 Cu

10 In-gas-cell laser spectroscopy of 57,59 Cu: a sample of spectra Cu + + e - First Ionization Limit cm-1 Autoionizing State 65 Cu cm -1 λ 2 = nm 4 P 0 1/2 Atomic spin: J=1/2 Nuclear spin: I π =3/2 - Total spin: F=1,2 F=2 F=1 63 Cu λ 1 = nm 59 Cu 2 S 1/2 CuI: ground state µ A ( Cu) µ A A hf 63 ( Cu) = ( Cu) 63 Ahf ( Cu) F=2 F=1 57 Cu: 6 ions/s Laser spectroscopy of 57,59 Cu Frequency [GHz]

11 In-gas-cell laser spectroscopy of 57,59 Cu: results [N.J. Stone,- PRC 77 (2008) ] [K. Minamisono,- PRL 96 (2006) ] [V.V. Golovko,- PRC 70 (2004) ] 57 Cu 199 ms 55 Ni 209 ms 56 Ni 6.0 d 57 Ni 36 h 58 Ni 55 Co 17 h 54 Co Laser spectroscopy of 57,59 Cu

12 In-gas-cell laser spectroscopy of 57,59 Cu: results Th. Cocolios,- PRL 103 (2009) , PRC 81 (2010) Interpretation with effective shell-model calculations of the copper isotopes: [Vingerhoets PRC 82 (2010) , Flanagan PRL 103 (2009) ]

13 Laser spectroscopy of Ag Nuclear structure below 100 Sn Preparation for a study of the 94 Ag isomers (I. Mukha et al., Nature 439 (2006) 289) F = 2 F = 1 Second step laser XeCl laser with unstable resonator I = 1/2 7.57eV 308 nm nm 2 P 3/2 I = 9/2 F = 6 F = 5 F = 4 F = 3 F = 1 F = 5 F = 0 2 S 1/2 F = 4

14 Laser spectroscopy of Ag Production 92 Mo( 14 N 130 MeV,2pxn) 104 x Ag 101 Ag 64,nat Zn( 36 Ar 125 MeV,pxn) Ag In-gas cell laser spectroscopy 520 mbar argon Total width: 9-10 GHz 5-7 scans per mass 99 Ag 97 Ag (T 1/2 =25.3 s) Detection Beta- and gamma detection

15 A Ag (I π =9/2 + ) Splitting (GHz) µ exp (nm) (9) 6.02(11)(2) (2) 5.80(2)(2) µ lit (nm) (2) 5.57(2)(2) 5.627(11) µ Schmidt (πg 9/2 )=6.294 nm GSI separator: U. Dinger,- NPA 503 (1989) 331 (21/2 + ) 100 Sn N=50 Z= E(2 + ) 1004 Mixing of the two configurations in the even Ag isomers: [Golovko, PRC81 (2010) ] N,Z=50 d 5/2 g 7/2 g 9/2 p 1/2 g=1.405(14)??? 1.34 (3) 1.289(8) 1.250(2) 1.266(1) 9/2 + 7/2 +

16 In-gas-cell laser spectroscopy using LIST: new opportunities Laser Ion Source Trap (LIST) High selectivity Improved total resolution Need for high-rep. rate lasers: >10kHz (pulse width ~100 µs) V RF Ion Guide [K. Blaum,- NIMB204 (2003) 331] [T. Sonoda,- NIMB 267 (2009) 2918] [I.D. Moore,- J. Phys. G31 (2005) s1499]

17 In-gas-cell laser spectroscopy: comparison gas cell vs. LIST Laser band width ~1.6 GHz (excimer pumped dye lasers) Reference cell nat Ni FWHM= ~ 2 GHz Red shift of 2.5 GHz: pressure dependence Pressure broadening Gas cell 58 Ni Ar 500 mbar FWHM=6.5 GHz Doppler shift due to jet velocity: ~560 m/s LIST FWHM= ~ 2 GHz 58 Ni Wavenumber [cm -1 ]

18 Pressure shift and pressure broadening of Cu and Ni resonance lines Cu + + e - First Ionization Limit cm-1 Autoionizing State λ 2 = nm Ar -1.9(1) MHz/mbar cm -1 4 P 0 1/2-5.5(3) MHz/mbar λ 1 = nm 2 S 1/ MHz/mbar CuI: ground state Ar 5.4 MHz/mbar Ni nm Cu nm

19 continuum Aut. state IP cm -1 Laser Ionization of Sn 1 P 1 3 P 0 λ 2 =454.9 nm λ 1 =254.7 nm cm λ Sn Shift = -150(10) MHz/mbar Broadening=210(25) MHz/mbar argon 500 mbar 390 mbar 300 mbar 200 mbar 150 mbar 100 mbar RC Current on SEM (na) Wavenumber (cm -1 )

20 Future plans and new opportunities for gas-cell based laser spectroscopy Develop the LIST mode for ultimate in-source laser spectroscopy measurements: Laval nozzle (Jet engines): long parallel jet, low pressure and low temperature Combined with high resolution high repetition rate laser system e.g. Ti:Sa laser (T. Kessler,- Laser Physics 18 (2008) 842) Total expected resolution about 200 MHz: detailed laser spectroscopy possible e.g.: in-source laser spectroscopy of Po isotopes: ISOLDE: Th. Cocolios,- PRL (2011) (see next talk) M. Seliverstof,- to be published B. Hansmann,- ChemPhysChem 8 (2007) 343 JYFL Th. Kessler, PhD thesis (2008) P. Karvonen,- EPJ 150 (2007) 283 I.D. Moore,- JPG G31 (2005) S1499

21 S3 at SPIRAL2 (GANIL ) High-intensity heavy ion beams: e.g. 48 Ca: >10 pµa Production of exotic nuclei using heavy-ion fusion evaporation reactions Super Separator Spectrometer: S3 Coupling with the LISOL gas-cell based laser ion-source concept No primary beam in the gas cell!!!

22 S3 at SPIRAL2 (GANIL ) Expected rates: e.g. 94 Ag and heavy elements: S3 transmission: 50% (5 charge states) Total efficiency (stopping, transport, laser ionization): 9 % 58 Ni( 40 Ca,p3n) 94 Ag: few 10 pps (plans at GSI SHIPTRAP) 208 Pb( 48 Ca,2n) 254 No: about 5 pps heavy ion beam Challenges: 100 Sn region isobaric contamination, selective detection, Actinides and trans-actinide region atomic theory, delay times, isobaric cont.,

23 (Gas-cell based) laser spectroscopy EURISOL: laser spectroscopy studies give key nuclear properties determined in a model-independent way (provided the atomic physics is known) [Kluge,- Spec, Acta B58 (2003) 1031 and Hyp. Int. 196 (2010) 295] complementary study of refractory type elements and actinides is essential production of isomeric beams with laser ionization: e.g. transfer/knock-out reactions [Stefanescu,- PRL98 (2007) ] intense RIB to produce new actinide isotopes for laser spectroscopy studies n-induced fission of 238 U after stopping fission products in a gas cell