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  1. Addendum INTC-P-183 (IS427) Nuclear moments and charge radii of Mg isotopes from N=8 up to (and beyond) N=20 University of Mainz: K. Blaum, M. Kowalska, R. Neugart, W. Nörtershäuser University of Leuven: K. Flanagan, P. Himpe, P. Lievens, G. Neyens, N. Vermeulen, D. Yordanov, M. De Rydt Outline Motivation and experimental procedure Recent Results on neutron-rich Mg Status of P-183, planned measurements Beam time request

  2. 13 12 • (1) Nuclear structure approaching the proton drip line / mirror nuclei. • - determine ground state spin/parity of 21Mg • - test of isospin symmetry in sd-shell: •  magnetic moments of T=3/2 mirror pair 21Mg – 21F 11 10 • (2) Nuclear structure around N=20: borders of the ‘Island of Inversion’ • - determine spin/parity of 31,33Mg ground states (and isomeric states) • - g-factor and Q-moments • single particle structure, admixture with 2p-2h intruder states • - shape coexistence in the N=20 region 20 8 Motivation • (3) Deformation changes between N=8 and N=20

  3. 21Mg: Physics Cases • We would like to answer the following open questions: • What happens at N=9 when approaching the proton drip line?Ground-state spin will allow to investigate possible changes in the shell structure. • Does the 21Mg-21F (Ip=5/2+) mirror pair (T=3/2) behave as expected? • Does there exist a skin or halo structure in the 21Mg isotope? Literature: Phys. Lett. B 307 (1993) 278; Nucl. Instrum. Meth. B 126 (1997) 423; Phys. Rev. C 36 (87) 1202; Nucl. Phys. A 693 (2001) 63; Nucl. Phys. A 704 (2002) 98c.

  4. Proposed Measurements Neutron-Rich Mg Ground state properties of neutron-rich Mg isotopes • - spin/parity of 29,31,33Mg groundstates • electromagnetic momentsm of 27,29,31,33Mg and Q of 29Mg • charge radii of24-27Mg • configuration of nuclear states • excitations acrossmagic N=20 • Where are borders of “island of inversion”? • Is N =20 magic in this region?

  5. Optical N detection Beam deflector (weak) Guiding field o Scintillator 0 RF coil s s s s s Laser + + + + + + + + + + + + + + + + + + + + Crystal + + o Scintillator 180 + +/ - 5kV + s Doppler tuning + Mg beam from voltage ISOLDE, 60keV (strong) NMR field D 25 25 HFS of Mg Mg HFS of 6.5 A(S1/2) = 596.5(5) MHz photons • Measure: • HFS -> m and Q • isotope shift -> 300 350 400 250 250 fine Doppler tuning voltage (V) fine COLLAPS Laser Spectroscopy Setup Procedure: Suitable for longer lived (>1s) and stable isotopes - Scan HFS by Doppler tuning the velocity of the ions/atoms - Observe fluorescence from ions/atoms excited by laser light - HFS resonances are seen in higher intensity of detected photons

  6. Optical N detection Beam deflector (weak) Guiding field o Scintillator 0 RF coil s+ s s s s laser + + + + + + + + + + + + + + + + + + + + Crystal + + o Scintillator 180 + +/ - 5kV + Doppler tuning s voltage + Mg beam from ISOLDE, 60keV (strong) NMR field b decay asymmetry Spin polarisation by optical pumping Suitable for short- lived isotopes (<1s) Decoupling of atomic and nuclear spins 31Mg HFSobserved inb-decay asymmetry,by changing ion velocity Measure: HFS -> I, m and Q b-NMR -> |g| and Q Ion velocity set to highest asymmetry, NMR scan by changing rf frequency Larmor frequency seen as drop in asymmetry COLLAPS Setup for b-NMR Procedure:

  7. . n 29Mg h |g | = L . m I B N b-asymmetry (%) nL(29Mg) = 1426.3(20)kHz in MgO Radiofrequency (MHz) 8Li nL(8Li) = 1807.03(2) kHz -1.9 31Mg (reference) 10 -2.2 in MgO 9 b-asymmetry (%) -2.5 8 b-asymmetry (%) -2.8 in MgO 7 nL(31Mg) = 3859.73(18) kHz in MgO Radiofrequency (MHz) 6 Table value: guncorr(8Li) = 0.826693(9) Radiofrequency (MHz) b-NMR: g-Factor of 29,31Mg to eliminate uncertainty of external magnetic field (B) -> reference measurement for nucleus with known m |g(29Mg)| = 0.653(1) M. Kowalska et al., in preparation |g(31Mg)| = 1.7671(3) G. Neyens et al.,Phys. Rev. Lett. 94, 022501 (2005)

  8. For 29Mg in the same way: I=3/2+ confirmed m=+0.9795(12) mN HFS and b-NMR: m and I Hyperfine structure NMR in MgO crystal DE acceleration voltage radiofrequency DE = 3070(50) MHz (and m<0) |g| = 1.7671(3) ref = 25Mg Independent determination of: Ground state spin of 31Mg: Magnetic moment: m = - 0.88355(15)mN Ip = 1/2+ G. Neyens et al.,Phys. Rev. Lett. 94, 022501 (2005)

  9. Status and Proposed Measurements • - spin of 21Mg groundstate • electromagnetic moments(m,Q) of 21,23Mg • charge radii of23-30Mg

  10. Mg: Runs and Problems in 2003-2006 2003: - Test run on 29,31Mg to demonstrate b-NMR detection SUCCESSFUL 2004:- Run 1: b-NMR on 29,31Mg (g, Q, Spin) SUCCESSFUL (~12 shifts) - Run 2: optical detection 24,25,26,27Mg (radii and m(27Mg)) partly SUCCESSFUL (but target failed after 6 shifts) 2005: - Run 1: b-NMR on 33Mg FAILED(due to target failure after two hours of protons) - Run 2: b-NMR on 33Mg FAILEDPARTIALLY(only A factor could be measured; HT=40 kV and extremely low yield; a few shifts taken) 2006: - Run 1: b-NMR on 33Mg FAILED(only 5% transmission and factor of 10 less yield due to wrong line polarity)

  11. Conclusion IS427 and Beam-Time Request • So far only two successful runs on 29,31Mg; (see e.g. G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2004)) one more run on 33Mg (spin, g, Q) pending (in total ~35 shifts) • One more run on neutron-rich Mg isotopes for optical and NMR isotope shift measurements is requested (8 Shifts) • Two runs on neutron-deficient Mg isotopes (mainly 21Mg) for spin assignment, g-factor and quadrupole moment measurements are requested (2*8 shifts) • One test run on neutron-deficient Mg isotopes is requested in order to find best target-ion source combination (6 shifts) We ask for one test run on 21Mg and 24 radioactive beam shifts for the completion of IS427.

  12. The IS427 Collaboration K. Blaum1,2*, K. Flanagan3, P. Himpe3, M. Kowalska1, P. Lievens4, R. Neugart1, G. Neyens2**, W. Nörtershäuser1,2, N. Vermeulen3, M. De Rydt3, D. Yordanov3 1 Instititut für Physik, Universität Mainz, Mainz, Germany2 Gesellschaft für Schwerionenforschung, Darmstadt, Germany 3 Instituut voor Kern en Stralingsfysica, KULeuven, Belgium 4 Laboratorium voor Vastestoffysica en Magnetisme, KULeuven, Belgium * Supported by Helmholtz-Association for National Research Centres and BMBF Contract Number: 06 MZ 175 I ** Supported by FWO Vlaanderen, G-0445.05 Thanks for the support by the ISOLDE technical group.

  13. 14 Si 22 Si 23 Si 24 Si 25 Si 26 Si 27 Si 28 Si 29 Si 30 Si 31 Si 32 Si 33 Si 34 Si 35 Si 36 Si 37 Si 38 Si 39 Si 40 Si 41 Si 42 13 Al 22 Al 23 Al 24 Al 25 Al 26 Al 27 Al 28 Al 29 Al 30 Al 31 Al 32 Al 33 Al 34 Al 35 Al 36 Al 37 Al 38 Al 39 36S: 16p and 20n Mg 29 12 Mg 20 Mg 21 Mg 22 Mg 23 Mg 24 Mg 25 Mg 26 Mg 27 Mg 28 Mg 30 Mg 31 Mg 32 Mg 33 Mg 34 Mg 35 Mg 36 26 protons neutrons 1p1/2 11 Na 19 Na 20 Na 21 Na 22 Na 23 Na 24 Na 25 Na 26 Na 27 Na 28 Na 29 Na 30 Na 31 Na 32 Na 33 Na 34 Na 35 0f5/2 fp- shell 1p3/2 10 Ne 16 Ne 17 Ne 18 Ne 19 Ne 20 Ne 21 Ne 22 Ne 23 Ne 24 Ne 25 Ne 26 Ne 27 Ne 28 Ne 29 Ne 30 Ne 32 24 0f7/2 9 F 15 F 16 F 17 F 18 F 19 F 20 F 21 F 22 F 23 F 24 F 25 F 26 F 27 F 29 22 8 O 12 O 13 O 14 O 15 O 16 O 17 O 18 O 19 O 20 O 21 O 22 O 23 O 24 18 20 0d3/2 7 N 11 N 12 N 13 N 14 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 sd- shell 1s1/2 16 S 27 S 28 S 29 S 30 S 31 S 32 S 33 S 34 S 35 S 36 S 37 S 38 S 39 S 40 S 41 S 42 S 43 S 44 S 45 S 46 S 47 S 48 34 15 P 26 P 27 P 28 P 29 P 30 P 31 P 32 P 33 P 34 P 35 P 36 P 37 P 38 P 39 P 40 P 41 P 42 P 43 P 44 P 45 P 46 32 0d5/2 8 “normal” 32Mg:12p and 20n protons neutrons 1p1/2 0f5/2 fp- shell 1p3/2 0d3/2 0f7/2 sd- shell 1s1/2 0d5/2 inversion of levels Region of Interest: „Island of Inversion“ • 1975: excess in binding energy in nuclei around Z=11 and closed shell N=20 ->attributed to large deformations • Shell model interpretation: levels from fp-shell (above N=20 shell gap) are filled (with sd-shell still open)at low excitation energies, or even in ground states(mixing of states from sd and fp shells) • => unexpected, since N=20 should be a shell gap

  14. Atomic hyperfine structure (interaction of nuclear and atomic spins) Nuclear Magnetic Resonance – NMR (Zeeman splitting of nuclear levels) HFS COLlinear LAser SPectroscopy To measure ground state properties of nuclei, based on: Isotope shifts in atomic transitions (change in mass and size of different isotopes of the same chemical element) Isotope shift Isotope A Isotope A’

  15. HFS of 25,27Mg D1 line D1 line Ags = -1432(4) MHz Aex = -248(4) MHz Ags = -596.4(9) MHz Aex = -102.8(3) MHz Ref. for Ags(25Mg) = -596.254376(54) Preliminary results: m(25Mg) = -0.854(2) mN - in agreement with literature: m= -0.8555(1) Q(25Mg) = 160(40) mb - in agreement with literature: Q=199.4(2) m(27Mg) = -0.4109(33) mN

  16. DEHFS = -3070(50) MHz b-Asymmetry Scans: HFS of 31Mg D2 line (similar plots and simulations for D1) Simulation (assuming I=1/2 and g<0) Indication of spin 1/2 and g <0 M. Kowalska et al., Eur. Phys. J. A 25, s01,193 (2005)

  17. cubic crystal non-cubic crystal in a in a Þ electric field gradient V zz m 3/2 I D D E E + ½ Q * V mag mag zz 1/2 D E I=3/2 D E mag mag - 1/2 D E mag D E - ½ Q * V - 3/2 mag zz n n L L P P max max polarisation polarisation Dn Dn L L n n . . RF RF D = m E g B mag I N . 1 D Q V E Þ Þ zz mag D n = 2 n = L L h h b-NMR: g-Factor and Quadrupole Moment

  18. 1/2+ -1.37 2500 E(keV) 5/2+ 1p1/2 0f5/2 1p3/2 n n … 3/2+ +0.64 E (keV) 0f7/2 1/2+ -0.84 1000 1p1/2 0d3/2 0f5/2 1s1/2 1p3/2 0d5/2 p 1p1/2 0f7/2 m I 0f5/2 max 2n 1p3/2 0f7/2 0d3/2 1s1/2 3/2(-) (7/2)- 500 1/2+ 0d5/2 -0.66 0d3/2 < -1.82 3/2- 1s1/2 0d5/2 3/2+ +0.65 (3/2-) < 5/2 < 5/2+ 7/2- -1.13 (3/2)+ 7/2- -1.12 (3/2)+ 3/2+ +1.34 1/2+ 3/2- -1.84 -0.88355 0 decay data our m and Ip Monte Carlo Shell Model (SDPF-M) Utsuno et al. 2005 Shell Model (USD) Wildenthal et al. 1990 Shell Model(sdpf.iokin.si35) Nummela et al. 2005 assignements 2004-2005 Klotz et al. 1993 m and Ip of31Mg – theory Our spin/parity assignments to lowest lying levels Several neutrons excited across N=20 shell necessary to explain I=1/2+ for 31Mg