Nuclear moments and charge radii of Mg isotopes from N=8 up to (and beyond) N=20 Univ. Mainz: M. Kowalska, R. Neugart K.U.Leuven: D. Borremans, S. Gheysen, P. Himpe, P. Lievens, S. Mallion, G. Neyens, D.Yordanov, N. Vermeulen CERN: K. Blaum Spokesperson: Gerda Neyens Contact Person: Magda Kowalska INTC-P-183

Motivation Earlier and ongoing work: At ISOLDE: - ground state properties of the Na isotopes M. Keim et al., PhD Thesis, Univ. Mainz ENAM ’98 EJP A8 (2002) 31 and in preparation

Y. Utsuno, T. Otsuka et al. Progress of Theoretical Physics Supplement No. 146 (2002)488 MSCM calculations for Na isotopes Extract from the paper: “It is quite essential to study an isotope chain systematically from the normal-dominant to the intruder-dominant nuclei to examine the N =20 shell gap. In particular, nuclei at the boundary will give much information ! “ For 30 Na (N=18) the 2p2h configurations are mixed in the ground state by 40%, enlarging the quadrupole moment from the sd-shell value. At N =19 and 20 : a very good agreement for the MCSM  both ground states are dominated by the 2p2h configurations. Extra neutron correlations in the intruder configurations induce the change in deformation Data on Na-isotopes: M. Keim et al., ENAM ’98 and EJP A8 (2002) 31 MSCM calculations Including mixing between normal and intruder configurations

Motivation Earlier and ongoing work: At ISOLDE: - ground state properties of the Na isotopes - ground state properties of the Ne isotopes W. Geithner et al. PhD thesis, Univ. Mainz papers in preparation

A. Bhagwat and Y. K. Gambhir PHYSICAL REVIEW C 68, (2003) Recently observed charge radius anomaly in neon isotopes Relativistic mean field (RMF) calculations isotopic shifts (a) charge radii (b) Data on Ne-isotopes: W. Geithner, PhD thesis, papers in preparation Ne have strong prolate deformation (neutron deficient nuclei) The shape transition is observed between 23 Ne and 24 Ne. The higher neon isotopes have relatively milder deformations ! It turns out that except for 20-22,28Ne, all the neon isotopes have very small or zero neutron pairing energies. This reflects that the deformation effects are largely due to the protons.

Motivation Earlier and ongoing work: At ISOLDE (experiments finished): - ground state properties of the Na isotopes - ground state properties of the Ne isotopes At GANIL (experiments ongoing): - study of neutron rich Al-isotopes S. Teughels et al., PhD thesis K.U. Leuven D. Borremans et al., PLB 537 (2002) 45 D. Borremans et al., PRC 66 (2002) P. Himpe et al., PhD thesis KU Leuven, in preparation P. Himpe et al., in preparation

Systematic study of moments of Al isotopes D. Borremans et al., PLB 537 (2002) 45 P. Himpe et al., in preparation 32 Al : agreement with sd-shell model 34 Al: under investigation + study of Q-moments ! MCSM 33 Al: in between sd-shell model and MSCM I. Utsuno et al., PRC 64 (2001) (R) 31 Al : agreement with sd-shell model

Motivation Earlier and ongoing work: At ISOLDE (experiments finished): - ground state properties of the Na isotopes At GANIL (experiments ongoing): - study of neutron rich Al-isotopes - ground state properties of the Ne isotopes Started at GANIL  CONTINUE AT ISOLDE - GROUND STATE PROPERTIES OF Mg isotopes

Motivations (3) Deformation changes between N=8 and N=20 (1) Nuclear structure approaching the proton drip line / mirror nuclei. - determine ground state spin/parity of 21 Mg - test of isospin symmetry in sd-shell:  magnetic moments of T=3/2 mirror pair 21 Mg – 21 F (2) Nuclear structure around N=20: borders of the ‘Island of Inversion’ - determine spin/parity of 31,33 Mg 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

Experimental methods Collinear Laser Spectroscopy (COLLAPS) set-up Fine structure nl J 3s 1/2 ~10GHz 3p 1/2 3p 3/2 382 MHz 5/2 3/2 Hyperfine structure |I-J|  F  I+J 5/2 3/2 44 MHz I=2 ( 8 Li) 680 nm for Li 280 nm for Mg + (frequency doubling) Electron orbits nl ~ 10 6 GHz 3s 3p Measure hyperfine structure * optical detection of fluorescence light (need 10 6 ions/s) * detection of the  -asymmetry of optically polarized ions (polarized laser light) (need 10 3 ions/s) Hyperfine structure gives first information on - magnetic moment and sign ! - nuclear spin - mean square charge radius

Experimental methods Optical pumping +  -NMR  N1N1 N2N2 Optical pumping  - asymmetry ~ N 1 /N 2  -detection:  -hyperfine spectra  -NMR spectra N 1 /N 2 ~ Laser frequency  F1F1 F2F2 ++ D1-line, 8 Li  -Asymmetry   Q  [kHz] Li(Zn)  Q 11 Li(Si)  g rf [kHz]  - asymmetry

Feasibility: polarizing Mg ions D2-line ( 29 Mg + ) part of D2-line ( 31 Mg + ) Measured asymmetry for 31 Mg(MgO) Need for intense UV-light ! excitation from the ionic Mg + ground state to one of the first excited p-states, 3s 2 S 1/2  3p 2 P 1/2 or 3p 2 P 3/2 laser = 280 nm  requires a frequency doubling of CW dye laser radiation. Major investment (funds and manpower)  installed an external ring cavity for efficient frequency doubling of the available dye laser radiation at 560 nm.  gained factor 10 in laser power compared to doubling with internal cavity (test run october 2003).

(1) neutron rich isotopes: UC 2 -target 29 Mg - 31 Mg - 33 Mg beams OBSERVED RATES ions/pulse BEAM TIME REQUEST We request 35 shifts. We can report on the project status after 1 year.   -NMR techniques applicable on all isotopes (g-factor, Q-moments)   -asymmetry measurement of hyperfine structure (spins and sign  FOR ODD ISOTOPES)  optical detection of hyperfine structure applicable for radioactive 27 Mg, 29 Mg (spins, sign of , charge radii) radioactive 28 Mg, 30 Mg (charge radii) stable 24 Mg, 25 Mg, 26 Mg (spins, , charge radii) (2) neutron deficient isotopes: SiC target 21 Mg, 23 Mg yields to be tested ! 23 Mg: g and Q measured  can serve as calibration

Beam time request Neutron rich isotopes: (1) hyperfine spectra of polarized 29 Mg, 31 Mg, 33 Mg beams 5 shifts (2)  -NMR in cubic MgO crystal (g-factor) 29 Mg, 31 Mg, 33 Mg beams 9 shifts (3)  -NMR/LMR in MgF 2 crystal (EFG for Q-moment) 29 Mg, 31 Mg, 33 Mg beams 15 shifts (4) reference measurement of larmor frequency of 8 Li 2 shifts (5) isotope shifts of even isotopes (optical detection) 3 shifts Neutron deficient isotopes: (1) hyperfine spectra of polarized 21 Mg, 23 Mg 4 shifts (2)  -NMR/LMR 8 shifts

(b) I=5/2 I=3/2 I=7/2 (a) (c) 31 Mg in Mg single crystal Level Mixing (  =15º) Conclusions: (1)a long-lived I=7/2 in 31 Mg (2) ratio of  /Q

- Position Q /  - Amplitudeorientation - Width angle  LMR : Level Mixing Resonance NIM A340 (1994) 555 G. Neyens et al. PRC 59 (1999) 1935 N. Coulier et al. PRC 63 (2001) N. Coulier et al. Polarization in the LMR -Number of resonances spin I - + distance between resonances