Outline

Nuclear moments and charge radii of Mgisotopes 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

Motivation and experimental procedure

Beam time request

Status of P-183, planned measurements

Recent Results on neutron-rich Mg

Addendum INTC-P-183 (IS427)Addendum INTC-P-183 (IS427)

Motivation

8 2010111213

(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 21Mg

- test of isospin symmetry in sd-shell: magnetic moments of T=3/2 mirror pair 21Mg – 21F

(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

We would like to answer the following open questions:

1) What happens at N=9 when approaching the proton drip line?Ground-state spin will allow to investigate possible changes in the shell structure.

2) Does the 21Mg-21F (I=5/2+) mirror pair (T=3/2) behave as expected?

3) Does there exist a skin or halo structure in the 21Mg isotope?

21Mg: Physics Cases

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.

Proposed Measurements Neutron-Rich Mg

- spin/parity of 29,31,33Mg ground states- electromagnetic moments of 27,29,31,33Mg and Q of 29Mg- charge radii of 24-27Mg

configuration of nuclear statesexcitations across magic N = 20

Where are borders of “island of inversion”?Is N =20 magic in this region?

mass 25 27 28 29 30 31 32 33Half-life stable 158 h 21 h 1.4 s 335 ms 230 ms 120 ms 90 ms

atoms/s 2x108 3x107 6x106 1x106 3x105 1.5x105 104

spin-parity 5/2+ 1/2+ 0+ 3/2+ 0+ 1/2+ 0 (3/2, 7/2)-magn. mom. -0.85546 -0.4110

(15)

0 +0.9795

(15)

0 -0.88355

(15)

0 (-0.49,

-0.24)

Ground state properties of neutron-rich Mg isotopes

COLLAPS Laser Spectroscopy Setup

Measure:

- HFS -> and Q- isotope shift -> r 2r 2

Suitable for longer lived (>1s) and stable isotopes

- HFS resonances are seen in higher intensity of detected photons

Procedure:

- Scan HFS by Doppler tuning the velocity of the ions/atoms

Doppler tuningvoltage

+/- 5kV

(strong) NMR field

(weak) Guiding field

Beam deflector

Opticaldetection

Mg beam fromISOLDE, 60keV

+

Crystal

RF coil Scintillator 0o

+ +Laser + + ++ + + +

++

+++ ++ ++ ++ ++++

Scintillator 180 o

s

N

- Observe fluorescence from ions/atoms excited by laser light

fine250

25MgHFS of

A(S1/2) = 596.5(5) MHz

300 350fine Doppler tuning voltage (V)

250 400

phot

ons

25 MgHFS of

6.5

COLLAPS Setup for -NMR

Suitable for short- lived isotopes (<1s)

Measure: HFS -> I, and Q-NMR -> |g| and Q

Procedure:

Decoupling of atomic and nuclear spins

Doppler tuningvoltage

+/- 5kV

(strong) NMR field

(weak) Guiding field

Beam deflector

Opticaldetection

Mg beam fromISOLDE, 60keV

+

Crystal

RF coil Scintillator 0

o

+ + laser + + ++ + + +

++

+++ ++ ++ ++ ++++

Scintillator 180 o

s

N

Spin polarisation by optical pumping

-100 0-50 50 100Doppler tuning voltage (V)

-100 0-50 50 100Radiofrequency (MHz)

10 10 -

asy

mm

etr

y

HFS scan

-NMR-a

sym

me

try

31Mg

HFS observed in -decay asymmetry, by changing ion velocity

decay asymmetry )180()0(

)180()0(

NN

NN

Ion velocity set to highest asymmetry, NMR scan by changing rf frequency

Larmor frequency seen as drop in asymmetry

-NMR: g-Factor of 29,31Mg

Radiofrequency (MHz)

10

9

8

7

6

31Mg

in MgOL(31Mg) =

3859.73(18) kHz

-as

ymm

etry

(%

)

Bh|g |

N

LI

.

.

|g(31Mg)| = 1.7671(3)

to eliminate uncertainty of external magnetic field (B) -> reference measurement for nucleus with known

Radiofrequency (MHz)

-as

ymm

etry

(%

)

in MgO

-1.9

-2.2

-2.5

-2.8

8Li(reference)

in MgO

Table value: guncorr(8Li) = 0.826693(9)

L(8Li) =1807.03(2) kHz

Radiofrequency (MHz)1.40 1.41 1.42 1.43 1.44 1.45 1.46

18.05

18.10

18.15

18.20

18.25

18.30

18.35

18.40

asy

mm

etr

y (%

)

radiofrequency (MHz)

29Mg

in MgOL(29Mg) =

1426.3(20) kHz

-as

ymm

etry

(%

)

|g(29Mg)| = 0.653(1)

G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2005)

M. Kowalska et al., in preparation

HFS and -NMR: and IHyperfine structure

acceleration voltage

E

(and <0)E = 3070(50) MHz

ref

ref

g

AIgE )2/1(

I = 1/2+

Ground state spin of 31Mg: Magnetic moment:

= - 0.88355(15) N

Independent determination of:

ref = 25Mg

G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2005)

For 29Mg in the same way:

I=3/2+ confirmed=+0.9795(12) N

NMR in MgO crystal

radiofrequency

|g| = 1.7671(3)

Status and Proposed Measurements

- spin of 21Mg ground state- electromagnetic moments (Q) of 21,23Mg- charge radii of 23-30Mg

mass 21 22 23 24 25

Half-life 122 ms 3.8 s 11.3 s stable stable

atoms/s ? ~1000 2x105

spin-parity ? 0+ 3/2+ 0+ 5/2+

magn. mom. ? 0 -0.5364(3) 0 -0.85546

mass 25 27 28 29 30 31 32 33

Half-life stable 158 h 21 h 1.4 s 335 ms 230 ms 120 ms 90 ms

atoms/s 2x108 3x107 6x106 1x106 3x105 1.5x105 104

spin-parity 5/2+ 1/2+ 0+ 3/2+ 0+ 1/2+ 0 (3/2, 7/2)-magn. mom. -0.85546 -0.4110

(15)

0 +0.9795

(15)

0 -0.88355

(15)

0 (-0.49,

-0.24)

Mg: Runs and Problems in 2003-2006Mg: Runs and Problems in 2003-2006

2003: - Test run on 29,31Mg to demonstrate -NMR detection SUCCESSFUL

2004: - Run 1: -NMR on 29,31Mg (g, Q, Spin) SUCCESSFUL (~12 shifts)- Run 2: optical detection 24,25,26,27Mg (radii and 27Mg)) partly SUCCESSFUL (but target failed after 6 shifts)

2005: - Run 1: -NMR on 33Mg FAILED (due to target failure after two hours of protons)

- Run 2: -NMR on 33Mg FAILED PARTIALLY (only A factor could be measured;

HT=40 kV and extremely low yield; a few shifts taken)

2006: - Run 1: -NMR on 33Mg FAILED (only 5% transmission and factor of 10 less yield due to wrong line polarity)

Conclusion IS427 and Beam-Time RequestConclusion 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.

The IS427 CollaborationThe 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, Germany 2 Gesellschaft für Schwerionenforschung, Darmstadt, Germany3 Instituut voor Kern en Stralingsfysica, KULeuven, Belgium4 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 supportby the ISOLDE technical group.

14Si22

Si23

Si24

Si25

Si26

Si27

Si28

Si29

Si30

Si31

Si32

Si33

Si34

Si35

Si36

Si37

Si38

Si39

Si40

Si41

Si42

13Al22

Al23

Al24

Al25

Al26

Al27

Al28

Al29

Al30

Al31

Al32

Al33

Al34

Al35

Al36

Al37

Al38

Al39

12Mg20

Mg21

Mg22

Mg23

Mg24

Mg25

Mg26

Mg27

Mg28

Mg30

Mg31

Mg32

Mg33

Mg34

Mg35

Mg36

26

11Na19

Na20

Na21

Na22

Na23

Na24

Na25

Na26

Na27

Na28

Na29

Na30

Na31

Na32

Na33

Na34

Na35

10Ne16

Ne17

Ne18

Ne19

Ne20

Ne21

Ne22

Ne23

Ne24

Ne25

Ne26

Ne27

Ne28

Ne29

Ne30

Ne32

24

9F15

F16

F17

F18

F19

F20

F21

F22

F23

F24

F25

F26

F27

F29

22

8 O12

O13

O14

O15

O16

O17

O18

O19

O20

O21

O22

O23

O24

18 207

N11

N12

N13

N14

N15

N16

N17

N18

N19

N20

N21

N22

N23

8

Mg29

16S27

S28

S29

S30

S31

S32

S33

S34

S35

S36

S37

S38

S39

S40

S41

S42

S43

S44

S45

S46

15P26

P27

P28

P29

P30

P31

P32

P33

P34

P35

P36

P37

P38

P39

P40

P41

P42

P43

P44

P45

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

32Mg: 12p and 20n

fp-shell

sd-shell

1p3/2

0f7/2

0f5/2

0d5/2

1s1/2

0d3/2

1p1/2

protons neutrons

inversion of levels

fp-shell

sd-shell

1p3/2

0f7/2

0f5/2

0d5/2

1s1/2

0d3/2

1p1/2

protons

36S: 16p and 20nneutrons

“normal”

COLlinear LAser SPectroscopy

To measure ground state properties of nuclei, based on:

HFS

)1()1()1( where JJIIFFK

JIJI

JJIIKKBK

AEHFS

)12)(12(2

)1()1()1(

243

JI

HA eI

)0()0(zzeQVB

Atomic hyperfine structure(interaction of nuclear and atomic spins)

zzNImag VQBgE 2

1

Nuclear Magnetic Resonance – NMR(Zeeman splitting of nuclear levels)

0B0B

',2',

'

')(

AA

SMSNMSAA rF

AA

AAKK

Isotope shifts in atomic transitions(change in mass and size of different isotopes of the same chemical element)

Isotope shift

Isotope A Isotope A’

HFS of 25,27Mg

27Mg

LineVoltage [V]

Coun

ts in

Scale

r 7 []

-1.5 -1 -0.5 0 0.5

84000

84500

85000

85500

86000

86500 D1 line25Mg

LineVoltage [V]

Cou

nts

in S

cale

r 7

[]

4.5 5 5.5 6 6.5 7 7.5 8 8.5

5000

6000

7000

8000

9000 D1 line

Ags = -596.4(9) MHzAex = -102.8(3) MHz

Ags = -1432(4) MHzAex = -248(4) MHz

Ref. for Ags(25Mg) = -596.254376(54)

Preliminary results:

(25Mg) = -0.854(2) N

- in agreement with literature: -0.8555(1)

Q(25Mg) = 160(40) mb - in agreement with literature: Q=199.4(2)

(27Mg) = -0.4109(33) N

-Asymmetry Scans: HFS of 31Mg

EHFS = -3070(50) MHz

M. Kowalska et al., Eur. Phys. J. A 25, s01,193 (2005)

D2 line (similar plots and simulations for D1) Simulation(assuming I=1/2 and g<0)

Indication of spin 1/2 and g <0

-NMR: g-Factor and Quadrupole Moment

in a cubic crystal

NImag BgE

h

EmagL

-3/2

-1/2

1/2

3/2Emag

I=3/2

mI

Emag

Emag

RF

Pmax

L

..

pola

risat

ion

B

hg

NLI

electric field gradient V zz

h

VQ zzL 2

1

Emag + ½ Q * Vzz

Emag

Emag - ½ Q * Vzz

RF

Pmax

L

LL

in a non-cubic crystal

.

pola

risat

ion

ZZL V

hQ

2

and I of 31Mg – theoryOur spin/parity assignments to lowest lying levels

our and I assignements2004-2005

1/2+

(3/2-)

(7/2)-

(3/2)+

I

-0.88355

Klotz et al.1993

decaydata

0

500

1000

2500

(3/2)+<5/2+

<5/2

3/2(-)<

E(k

eV

)

Shell Model (USD)

Wildenthal et al.1990

5/2+

1/2+

3/2+ +1.34

-1.37

1p3/2

0f7/2

0f5/2

0d5/2

1s1/2

0d3/2

1p1/2

Shell Model (sdpf.iokin.si35)Nummela et al.

2005

7/2- 3/2-

1/2+3/2+

-1.13 -1.84

-0.84+0.64

1p3/2

0f7/2

0f5/2

0d5/2

1s1/2

0d3/2

1p1/2

max 2

Monte Carlo Shell Model (SDPF-M) Utsuno et al.

2005

3/2-

7/2-

1/2+

3/2+

-1.82

-1.12

-0.66

+0.65

1p3/2

0f7/2

0f5/2

0d5/2

1s1/2

0d3/2

1p1/2

n …

Several neutrons excited across N=20 shell necessary to explain I=1/2+ for 31Mg