The Island of of Inversion from a nuclear moments perspective

Transcription

1 The Island of of Inversion from a nuclear moments perspective Gerda Neyens Instituut voor Kern- en Stralingsfysica, K.U. Leuven, Belgium the LISE-NMR GANIL: E437 (,32,33 g-factors) E437a ( 34, 35 Si g-factors + polarization in pick-up reactions) sd-shells S 36 P 35 fp-shells the COLLAPS ISOLDE-CERN Si Si Si Si 32 Si 33 Si 34 Si 35 Si 36 Si 37 IS427 ( 27,,,33 Mg spins and g-factors) First introduced: Warburton, Becker, Brown, PRC41(2000)1147 ground state dominated by neutron excitations from sd to fp shells 20 pf Mg 27 Na 26 Ne 25 Mg 28 Na 27 Ne 26 Mg Na 28 Ne 27 Mg Na Ne 28 Mg Na Ne Mg 32 Na Ne Mg 33 Na 32 Mg 34 Na 33 Ne 32 Mg 35 Na 34 sd F 24 F 25 F 26 F 27 F

2 To To measure nuclear nuclear moments need need spin-polarized polarized beams beams In-flight projectile fragments LISE-GANIL Spin-orientation from the reaction process and in-flight selection procedure - typically about % orientation (polarized or aligned beam) - all elements Isotope Separation On-Line ISOLDE-CERN Spin-orientation from resonant interaction between 60 kev radioactive beam and a circularly polarized laser beam - typically about 10-% polarization - only particular elements (Li, Be, Na, Mg, ) Last 3 years systematic study of the orientation process - in projectile fragmentation - in nucleon pick-up reactions now very well understood!

3 Improving experimental GANIL GANIL (1) (1) How How measure polarization in in a fragment beam beam? Via detection of b-asymmetry: R = N up /N down ~ A exp (1-2A. P) measure change between non-polarized and polarized ensemble: R 0 ~ A exp R ~ A exp P NMR-magnet b- detectors RF-coil crystal de-polarize the beam to measure R 0 (a) by β-nuclear Magnetic Resonance (need to know g-factor) B POLARISED Radioactive Beam (b) by putting B=0 fast! b-asymmetry (%) (gives upper limit) R B /R 0 R NMR /R Si

4 Improving experimental GANIL GANIL (2) (2) Optimize the the polarization in in the the selected fragment beam beam!! (a) New crystal holder fast test of polarization in different crystals NMR-magnet POLARISED Radioactive Beam b -asymmetry (%) B1 detectoren 0 for 0,5 1 1,5 2 2,5 3 3,5 Si MgO NaCl b- detectors RF-coil crystal B beam crystal holder rf-coil degrader

5 Improving experimental GANIL GANIL (2) (2) Optimize the the polarization in in the the selected fragment beam beam!! (b) Measure polarization as function of selected fragment momentum 36 S (77 MeV/u) + 9 Be (185 mg/cm 2 ) target at LISE CSS MeV/u target LISE Fragment Separator secondary -beams purity > 90% b-nmr set-up 5-10 MeV/u CSS1 Ion source 36 S ions

6 Improving experimental GANIL GANIL (2) (2) Optimize the the polarization in in the the selected fragment beam beam!! (b) Measure polarization as function of selected fragment momentum Fragmentation S (77 MeV/u) + 9 Be (185 mg/cm 2 ) fragmentation: largest P in WING of the yield curve where production rate is lowest K. Turzó et al., PRC 73, 0443(2006) 34 1n pick-up as(%) Dp f p 0 1n pick-up: largest P in CENTER of the yield curve where production rate is max. Dp f p 0 modeling the reaction orientation: only 1 parameter, θ R ~ 10! good description of trendline also good for pick-up! Dp f p 0

7 Published results results on on moments in in island island of of inversion Outside island of inversion Inside island of inversion 33 Yet undecided Na at ISOLDE (COLLAPS) M. Keim et al, EPJA 8, (2000) M. Keim,, AIP Conf. Prof.455 (1998) ground states of Na, Na and Na contain 50%, 100% and 100% intruder conf. (2p2h / 4p4h) T. Utsuno et al., PRC 70, 0447(2004) -, the first polarized beam for β-nmr at GANIL D. Borremans et al., Phys. Rev. C 66,, (2002) ground states of is a normal sd-shell state D. Borremans et al., Phys. Lett.. B 537, 45 (2002) - Mg at ISOLDE (COLLAPS) G. Neyens et al., PRL 94, (2005) pure 2p-2h intruder ground state with I p = ½ + - Mg at GANIL (LISE E4b): β-decay confirms F. Marechal et al., PRC C72, 0444 (2005)

8 Recent Recent studies studies in in island island of of inversion At GANIL investigate isotopes using fragmentation (,32,33 ) and pick-up reactions ( 34, 35 Si) At ISOLDE towards 33 Mg β-nmr on A in Si crystal (ν RF = 1100 khz) P. Himpe et al., submitted to PLB, 2006 P. Himpe et al., Ph.D. Thesis, K.U. Leuven,, June 2006

9 g-factors of of isotopes up up to to N=20: N=20: indication for for intruder state state admixture into into ground ground state state sdpf 0p-0h experiment SDPF-M sdpf 2p-2h Na = 100% intruder state Calculations: sdpf ANTOINE code (Nummela et al., PRC63, 0446(2001). free-nucleon g-factors Utsuno et al., PRC70, 0447(2004) effective g-factorsg protons: in sd-shell neutrons: in sd-shell 2 neutrons in f 7/2 p 3/2 orbits (0p-0h) (2p-2h) sd 1d 3/2 2s 1/2 1d 5/2 20 2p 3/2 1f 7/2 pf sd

10 g-factors of of isotopes up up to to N=20: N=20: indication for for intruder state state admixture into into ground ground state state Results from moments studies in island of inversion : sdpf 0p-0h Experiment SDPF-M sdpf 2p-2h Na = 100% intruder Utsuno et al., PRC70, 0447(2004) effective g-factorsg Calculations: sdpf ANTOINE code (Nummela et al., PRC63, 0446(2001). free-nucleon g-factors 33 = 50% intruder Utsuno et al., PRC64, 0111 R(2001) sdpf 0p-0h SDPF-M eff SDPF-M free sdpf 2p-2h

11 Z=20 Z=18 Z=16 Ca K Ar Cl S P N=21 N=21 isotones: g-factors of of Si, Si, (GANIL) and and Mg Mg (ISOLDE) N=20 Calculation: 1 neutron in ν(f 7/2 p 3/2 ) orbits (sdpf interaction) effect Z=20 and Z=8 shell closures effect of Z=14 subshell closure g-factors approach free-nucleon value 34 and 35 Si 1n pick-up reaction 34 I π =(4 - ) N=21 isotones: ground state dominated by odd nf 7/2 g=0.541(1) Calculated g-factor for I p =7/2 - -0,3-0,35-0,4-0,45-0,5 Experiment: -0,55 - Z=20 is not a good shell closure (known, PLB522 (2001)). - subshell closure at Z=14 confirmed for N~20-0,6 Z=8 P. Himpe et al., Ph.D. Thesis, KU Leuven Z=12 PRL 2006, in preparation 35 Si I π =(7/2 - ) Z=14 Schmidt value nf 7/2 g=0.468(1) Z=20 1,5 2,5 3,5 4,5 5,5 6,5 7,5 8,5 F Ne Mg Si S Ar Ca

12 N=21 N=21 isotones from from Ca Ca to to Mg: Mg: g-factors of of Si, Si, (GANIL) and and Mg Mg (ISOLDE) Z=20 Z=18 Z=16 Ca K Ar Cl S P N= Experimental and theoretical arguments: ground states of 33Mg, Ne, F are not normal 7/2- e.g. 33 Mg suggested (3/2,5/2)+ measure g-factor and spin of 33 Mg! Calculated g-factor for I p =7/2 - -0,3-0,35-0,4-0,45-0,5-0,55-0,6 Z=8 P. Himpe et al., Ph.D. Thesis, KU Leuven Z=12 PRL 2006, in preparation Z=14 Schmidt value nf 7/2 Z=20 1,5 2,5 3,5 4,5 5,5 6,5 7,5 8,5 F Ne Mg Si S Ar Ca

13 N=21 N=21 isotones from from Ca Ca to to Mg: Mg: g-factors of of Si, Si, (GANIL) and and Mg Mg (ISOLDE) P. Himpe et al., Ph.D. Thesis, KU Leuven Z=20 Z=18 Z=16 Ca K Ar Cl S P and 35 Si 1n pick-up reaction 34 I π =(4 - ) PRL 2006, in preparation g=0.540(1) deviation almost 50%!!! Comparison of g theo g exp 45,000 N=20 Calculations: sdpf ANTOINE code (Nummela et al., PRC63, 0446(2001). For 34 : free-nucleon g-factors protons in sd-shell 1 neutron in (f 7/2 p 3/2 ) orbits = 0p-0h state Dg (%) 35,000 25,000 15,000 5,000-5, isotope

14 N=21 N=21 isotones from from Ca Ca to to Mg: Mg: g-factors of of Si, Si, (GANIL) and and Mg Mg (ISOLDE) Z=20 Z=18 Z=16 Ca K Ar Cl S P N= Calculations: sdpf ANTOINE code (Nummela et al., PRC63, 0446(2001). For 34 : free-nucleon g-factors P. Himpe et al., Ph.D. Thesis, KU Leuven 34 and 35 Si 1n pick-up reaction 34 I π =(4 - ) protons in sd-shell 1 neutron in (f 7/2 p 3/2 ) orbits = 0p-0h state 3 neutrons in (f 7/2 p 3/2 ) orbits = 2p-2h state g=0.540(1) PRL 2006, in preparation Explanation: mixing of 0p- 0h and 2p-2h in ground state wave function 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 exp g( 34, 4 - ) 0p-0h 2p-2h 1 2

15 N=21 N=21 isotones from from Ca Ca to to Mg: Mg: g-factors of of Si, Si, (GANIL) and and Mg Mg (ISOLDE) P. Himpe et al., Ph.D. Thesis, KU Leuven PRL 2006, in preparation 34 I π =(4 - ) Explanation 2: the np 3/2 orbit is more occupied in ground state wave function reduce νf 7/2 p 3/2 gap g=0.540(1) Explanation: mixing of 0p-0h and 2p-2h in ground state wave function 0,8 0,7 g( 34, 4 - ) 0,8 0,7 g( 34, 4 - ) 0,6 0,5 0,4 0,3 exp p(sd) 5 nf 7/2 p(sd) 5 n(f 7/2 p 3/2 ) 0,6 0,5 0,4 0,3 exp 0,2 0,2 0,1 0,1 0 p(d 5/2 ) 5 nf 7/ p(d 5/2 ) 5 np 3/2 0 0p-0h 2p-2h 1 2

16 CONCLUSIONS AND AND OUTLOOK A CONSISTENT INTERPRETATION OF ALL MOMENTS IS NEEDED (1) The g-factor of 35 Si supports sub-shell closure at Z=14 doubly-magic 34 Si (2) The g-factor of 33,34 suggest mixing of 2p-2h configurations in their ground state (3) The g-factor (and spin) of Mg can be understood as a pure intruder ground state. The transition from normal nuclei to the island of inversion occurs gradually, both in N and Z Moments are very sensitive to this.

17 CONCLUSIONS AND AND OUTLOOK What can we do with β-nmr at SPIRAL2? - nuclei not accessible via fragmentation e.g. very neutron rich near 78 Ni, 132 Sn MAIN PROBLEM: contamination of isobars beam purity of 80% needed!!!! Polarize nuclei via optical pumping with resonant laser beam (not all elements) Hyperfine structure provides moments as well! (not all elements) BUT β-nmr can be applied to beams of 1000/s (sensitive method) AND combination of both leads to direct spin measurement

18 COLLABORATIONS Leuven/Mainz collaboration at ISOLDE/CERN Leuven: D. Borremans, P. Himpe, P. Lievens, S. Mallion, G. Neyens, N. Vermeulen, D. Yordanov, K. Flanagan Mainz: K. Blaum, M. Kowalska, R. Neugart The LISE-NMR collaboration at GANIL Leuven: D. Borremans, P. Himpe, K. Turzo, S. Mallion, G. Neyens, N. Vermeulen, D. Yordanov, K. Flanagan GANIL: C. Stodel, L. Perrot, F. de Oliveira Santos, G. Georgiev Camerino: D.L. Balabanski Bruyeres-le-Chatel: J.M. Daugas, V. Meot, G. Belier DUBNA: Yu.-E. Penionzhkevich

19 g-factors of of isotopes up up to to N=20: N=20: indication for for intruder state state admixture in in,20,,20, Na Na isotopes Results from moments studies in island of inversion : Na at ISOLDE (COLLAPS) M. Keim et al, EPJA 8, (2000) M. Keim,, AIP Conf. Prof.455 (1998) ground states of Na, Na and Na contain 50%, 100% and 100% intruders (2p2h / 4p4h) T. Utsuno et al., PRC 70, 0447(2004) From g-factor alone clear indication for intruder contribution in Na and Na only! quadrupole moments are more sensitive to deformation! Na contains also 50% intruders