K. Asahi Tokyo Institute of Technology (Tokyo Tech)

Nuclear structure studies with polarized radioactive beams

The 18th International Spin Physics Symposium (SPIN2008) 6 - 11 Oct. 2008, Univ. of Virginia, Charlottesville, Virginia, USA.

OUTLINE:

1. Spin in Low-energy Nuclear Structure Physics

2. History of the Spin-polarized/Aligned Radioactive Beams (RIB)

3. Nuclear Moment Measurements with Polarized/Aligned RIB

4. Recent Results on n-rich Al isotopes and the Island of Inversion

Neutron number N

Pro

ton

nu

mb

er Z

Chart of Nuclei

Nucleus: Many-body system of fermions of two types

(Nucleus along the stability line)

●Bunching of the single-particle levels

⇒ determines the Nuclear Structure

Nucleus: Many-body system of fermions of two types

2

16

6

increase of N/Z(Nucleus along the stability line) (Neutron-rich nucleus)

New magic numbers ??

●Bunching of the single-particle levels

⇒ determines the Nuclear Structure

In fact, the shell does evolve, ..... due to the tensor force.

is

・ attractive for j> - j<', j< - j>'

・ repulsive for j> - j>', j< - j<'

[Otsuka et al., PRL 95 (05) 232502]

[Otsuka et al., PRL 97 (06) 162501]● Monopole energy of the tensor interaction

T, '

2 1 ' '

2 1JTJ

j j

J

J jj V jjV

J

proton neutron

j'>

j'<

j>

j<

is

・ attractive for j> - j<', j< - j>'

・ repulsive for j> - j>', j< - j<'

[Otsuka et al., PRL 95 (05) 232502]

[Otsuka et al., PRL 97 (06) 162501]● Monopole energy of the tensor interaction

T, '

2 1 ' '

2 1JTJ

j j

J

J jj V jjV

J

proton neutron

j'>

j'<

j>

j<

proton neutron

j'>

j'<

j>

j<

In fact, the shell does evolve, ..... due to the tensor force.

Thus, the single-particle orbits may migrate leading to a possible change in shell structure.

Note that the s.p. orbits are characterized by the angular momentum j.

Also,

decoupling of neutron from the core

+++

eeff(n) 0.5

(in a normal nucleus)

eeff(n) 0 ??

core

(in a n-rich nucleus)

Such an effect can be detected through measurement of electric quadrupole moments Q associated with nuclear spin.

ebare(n) = 0

Thus, the spin plays

vital roles in structural change of nuclei

towards far from stability

Observation of spin-alignment in projectile fragments

RIKEN-GANIL collab.

(at LISE/GANIL, 1987)

14B

18O (60 MeV/u) 14B fragment

9Be target

2

1

0

6.094 MeV

Target

Projectile Fragment

Pfrag = Mv0 P'part

P'part = p'i

LFrag = R P'Part

PLB 251, 499 (1990)

Angular momentum introduced in a projectile fragmentin the intermediate-energy PF reaction

p'iv0

R

-- Angular momentum introduced in the fragment

(internal Fermi motion)

Spin polarization found in RI beams from PF reaction

z∥ ki kf

p||

Expected spin alignment in the 14B fragment

Goldhaber distribution

Result of the RIKEN-GANIL collab. experiment:

Alignment result at GANIL '87

Expected spin alignment in the 14B fragment

Goldhaber distribution

Result of the RIKEN-GANIL collab. experiment:

Polarization - at RIKEN, '90

Analyzer

L

43mSc (19/2) TD-PAD

Spin Rotation of aligned fragments, - at FRS/GSI, '93

Z. Phys. 350, 215 (1994)

　 B0 = 0.265 T

　 B0 = 0.265 T

RIPS/RIKEN, present

RIPS

K=540 RIKEN Ring Cyclotron

Isotope separationmagnetic analysis (A/Z)

+momentum-loss analysis (A2.5/Z1.5)

Production of spin polarizationscattering-angle selection

+momentum analysis

RIPS

Detector

Large-Z target

Detector

Small-Z target

near-side trajectory far-side trajectory

40AMeV

Au Nb Nb AlAu

70AMeV 110AMeV 70AMeV 70AMeV

H. Okuno et al., PL B 335, 29 (1994)

Fragmentation-induced spin polarization

● The kinematical model reproduce quite well the observed behavior of polarization P as a function of momentum and target Z-number.

● However, the observed ‥‥ magnitudes of P are by ～ 1/4 smaller than predicted.

•g-Factors measured at RIKEN–Boron isotopes : 14B, 15B, 17B–Carbon isotopes : 9C, 15C, 17C–Nitrogen isotopes : 17N, 18N, 19N–Oxygen isotopes : 13O–Fluorine isotopes : 21F–Aluminum isotopes : 23Al, 30Al, 32Al

•Q-moments measured at RIKEN–Boron isotopes : 14B, 15B, 17B–Nitrogen isotopes : 18N–Oxygen isotopes : 13O–Magnesium isotopes : 23Mg–Aluminum isotopes : 31Al, 32Al

TITech / RIKEN

Osaka / RIKEN

Spin-parity assignment

Reduction of E2 effective charges

Effect of n-excess

Spherical or deformed?

Nuclear moments measured at RIPS/RIKEN

●With spin-polarized fragment beams ....

<> from IS

●Reduction of effective charges

●Reduction of effective charges

pol 1n,p 0 1 '

0

2

' 2

1( ', ) 1

4 2

where

3/5

'

z z j j

j j

Z V N Z N Ze j j

A V A A

R

j r j

j'j ≈ 0.5 (sd orbits)

Thus, effective charges have been shown to reduce significantly as N/Z increases!

This also explains the anomalously hidered E2 transition in 16C reported recently.

GANIL (France)

g-factor: 18N, 32Cl, 31Al, 32Al, 33Al, 34Al, 35Si, ...

Q-moment: 18N, 31Al, 33Al, ...

MSU (U.S.A.)

g-factor: 9C, 35K, 57Cu, ...

Q-moment: 37K, ...

NIRS (Japan)

g-factor: 21F, 27Si, 35Ar, ...

Q-moment: 21F, 23Mg, 27Si, 39Ca, ...

RCNP (Japan)

Snow ball exp. with highly polarized 12B (P ~ 40 % !)

L

Many important works also at ... (a.f.a.I.k.)

●With spin-polarized fragment beams ....

(Matsuo, Furukawa, Shimoda et al.)

A precursor expt. for the recent development, "OROCHI" technique (Optical RI-atom Observation in Condensed Helium as Ion-catcher)

Polarization in pick-up channel(Groh, Mantica et al.)

Present status of the “Island of inversion”(Himpe et al.)

By including (Groh, Mantica et al., 2007)

● Improvements in prediction of P

・ Deorientation effect due to

-ray de-excitation 　　⇒ ×0.5

・ Out-of -plane acceptance 　　⇒ ×0.4

・ Angular distribution 　　⇒ ×0.1

Thus, now the magnitude of polarization that should be obtained in the experiment can be predicted in quite a useful accuracies!

LISE/GANIL (France)

g-factor: 61mFe(9/2+), 69mCu(13/2+), 67mNi(9/2+), ...

Q-moment: 61mFe(9/2+), ...

RISING/GSI (Germany) "g-RISING Campaign"

g-factor: 127mSn(19/2+), ...

●With spin-aligned fragment beams ....

61mFe(9/2+)

(RIKEN-GANIL Collab.)at LISE/GANIL, '87

RIPS/RIKEN '90

(RIKEN-Goettingen-GSI)FRS/GSI, '93

(RIKEN-TIT-GANIL-Leuven)LISE3/GANIL '08

RIBF/RIKEN Present

32Al isomer

E437b collaboration

• RIKEN Nishina Center• Tokyo Tech• Tohoku• KU Leuven• GANIL• Bruyères-le-Châtel• IPN Orsay• Sofia

E437b collaboration

• RIKEN Nishina Center• Tokyo Tech• Tohoku• KU Leuven• GANIL• Bruyères-le-Châtel• IPN Orsay• Sofia

43Sc isomer

(g-RISING Campaign)FRS/GSI, Present

at LISE3/GANIL '08

Recent result: Q-moments for 31,32,33Al

The experiment has been done in collaboration of

H. Ueno, K. A., K. Shimada, T. Nagatomo, A. Yoshimi, Y. Ichikawa, D. Kameda, T. Sugimoto, D. L. Balabanski, J. M. Daugas, K. Flanagan, G. Georgiev, S. Grevy, R. Lozeva, P. Morel, D. Nagae, G. Neyens, F. de Oliveira Santos, L. Perrot, M. De Rydt, C. Stodel, J. C. Thomas, N. Vermeulen, P. Vingerhoets, D. Yordanov, Y. Utsuno(E437b collaboration)

RIKEN, Tokyo Tech, Tohoku, Leuven, GANIL, Sofia, Bruyeres-le-Chatel, IPN Orsay, JAEA

● 31,32Al part: at RIPS/RIKEN

● 33Al part: at GANIL

Nuclear moment studies in the vicinity of the island of inversion

Ne

Mg

Al

Na

F

Si

P

20

Z

N

Island of Inversion Island of Inversion E.K. Warburton, J. A. Becker and B. A. Brown, PRC41(1990)1147.

MCSM with an sdpf model space:Y. Utsuno, et al., Phys. Rev. C 70 (2004) 044307.

20

s1/2

f7/2

d5/2

d3/2

p3/2

f7/2

d3/2

p3/2

Normal sd-shell configuration

d5/2

s1/2

0p0h, spherical 2p2h (intruder), deformed

Na isotopes

s1/2

d5/2

d3/2

f7/2

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

(j<)

d5/2(j>)

T=0 monopole interaction due to tensor force

[Otsuka et al., PRL 95 (05) 232502]

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

T=0 monopole interaction due to tensor force

[Otsuka et al., PRL 95 (05) 232502]

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

T=0 monopole interaction due to tensor force

[Otsuka et al., PRL 95 (05) 232502]

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

T=0 monopole interaction due to tensor force

[Otsuka et al., PRL 95 (05) 232502]

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

T=0 monopole interaction due to tensor force

[Otsuka et al., PRL 95 (05) 232502]

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

T=0 monopole interaction due to tensor force

[Otsuka et al., PRL 95 (05) 232502]

What would be happening in the IOI

00

What would be happening in the IOI

s1/2

d5/2

d3/2

f7/2

-- Gains correlation energies due to near degenerate f7/2 and d3/2 orbits

00

What would be happening in the IOI

[220]1/2

[211]1/2

[202]5/2

[211]3/2

[330]3/2

[200]1/2

-- Gains correlation energies due to near degenerate f7/2 and d3/2 orbits

Question:

Where and how steeply does this quantum phase transition take place as a function of N/Z ratio ?

5/2+

3+ 3+

5/2+

1+

5/2+5/2+

-

mom

ent ( N

)

μ (AAl)

μ(AAl) and Q(AAl)

RIKEN

RIKEN

Q (AAl)

• Qexp stays almost constant at N=14,15, but it becomes smaller at Qexp[32Al] → single-particle(hole)-like structure spherical shape

• Consistent with μ(AAl) - 27 ～ 32Al can be described within the sd- model space → normal configuration

→ 31,32Al are not related to island of inversion

Q

-mom

ent (

e· m

b)

0

50

100

150

200

expUSD

Large-scale shell model & aluminum isotopes

Y. Utsuno et al., PRC 64(2001)011301(R)

33Al

Z=13 is reallya "transitional number"

E. Caurier et al., PRC58(1998)2033

31Al 32Al 33Al 34Al

• decreases from 31Al(30Al)→33Al• E0p0h-E2p2h > 0 for Al isotopes, but similar to Mg, Na, Ne

30

29

31 32 33 34

31Al and 32Al

Primary beam 40Ar

95 AMeV, 40pnA

Nb target Nb, 0.37 g/cm2

Secondary beam 32Al

Emission angle 1.3 – 5.2 deg.

Momentum 12.6 GeV/c ±3 %

Intensity@F2 5 x 103 particle/sec.

Purity 85%

Polarization ~ 0.7 %

RIKEN Projectile fragment separator (RIPS):

B = (mv0 /e) AZ

= 3.6 m)

∝Z2 　 dEdx

Isotope separation:

Particle identification: • E @ F2 SSD • TOF (F2 PPAC - RRC)

Selected momentum region:

40Ar

LISE/GANIL

Target

Momentum dispersive plane

Achromaticfocal plane

-NMRapparatus

Emission angle: 2±1 deg.

Z

Aselection

5.1

5.2

Z

Aselection

PurityIntensity

36S16+

77.3 A MeV 3.8 e A

33Al

-NMR & -NMR Apparatus

Magnet pole

Plastic scintillators ~100mm I.d.

Spin-polarizedRI Beam

RF Coil~20 mm I.d.~0.1 mT, ~6 MHz

Stopper~22.5x28x1 mm3

-Al2O3 at 130 KSi at room temp.

rays

0.5 T

Production of the polarized 33Al beam

• Momentum analysis with the edge-shape degrader

33AlE

TOF

• Primary beam: 36S, 77.30 A MeV• Target: Be 1212 m • Beam-deflection angle: (2±1)°• Edge-shape degrader: Be, 1068 m• B: 3.1000 Tm• B: 2.9119 Tm

31Mg

32Mg

30Na

28Ne

Purity 75%

Momentum distribution

Gaussian fitting11.87±0.11 GeV/c

Accepted momentum region

Energy levels with eqQ interaction

124

1cos3 axis2

L1,

mc

Qmm

)12(2

3

IIh

eqQQ

h

Bg 0NL

13

128

1cos3 2axis2

0N

IIm

II

eqQmBgE c

m

1, mm

33Al

5.8 – 6.6 MHz

@ ～ 500 mT

33Al (I = 5/2+)m = -5/2

m = -3/2

m = -1/2

m = 1/2

m = 3/2

m = 5/2L

L

L

L

L

-5/2,-3/2

-3/2,-1/2

-1/2,1/2

1/2,3/2

3/2,5/2

0

0

q

B

0

0

q

B

0

0

q

B

Larmor frequency

Quadrupole coupling constant h

eqQ

Adiabatic Fast Passage -Nuclear Magnetic Resonance

0

0-

0+

t

Motion of a moment in a rotation coordinate system(with resonance freq. 0)

Frequency of the oscillating magnetic field B1

staticmagnetic

field

W ( )=1+AP cos A : Asymmetry parameter P : Polarization : Emission angle

NMReffect

(Up/Down)with RF

(Up/Down)w/o RF

(1-AP)/(1+AP)

(1+AP)/(1-AP)= = ~ 1 4AP

Adiabatic Fast Passage NMR

RF: 0=H/Ihe-

e-e-e-

e-e- e-e-e-

e-

-NMR/NQR method

RF signal for Q(33Al) measurement

L

L

L

L

L

-5/2,-3/2

-3/2,-1/2

-1/2,1/2

1/2,3/2

3/2,5/2

0,0 qB 0,0 qB 0,0 qB

= 5.8 – 6.6 MHz

18 ms

Larmor Frequency determination: NMR spectrum

6216.5 ± 6.5 kHzAP = 1.5%

Stopper: SiB0 = 498.8 mT g = 1.635

Preliminary

Q moment measurement: NQR spectrum

= 316 ± 55 kHz

Preliminary

)12(2

3Q

IhI

eqQ

Stopper: -Al2O3

B0 = 498.8 mTq = 67.701019 V/m2

|Q| = 129±22 emb

Comparison of Q moments with shell models

preliminary

Y. Utsuno, private communication

T. Nagatomo et al., to be published

0

10

20

30

40

50

60

70

29 30 31 32 33 34

Mass Number

I = 0g-factor known

Recent μ -measurements in the sd shell

μＱ

(Osaka G.)

N=20

E.K. Warburton et al., Phys. Rev. C 41, 1147 (1990)

Island of inversion

GANILISOLDE

RIKEN

M. Keim et al., Eur. Phys. J. A 8, 31 (2000). G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2005)

From recent experiments

G. Huber et al., Phys. Rev. C 18, 2342 (1978)

一連の Al 研究 (RIKEN, GANIL)

Summary

Fragmentation-induced spin polarization/alignment of RI beams has been developed and used for more than ten years.

This technique is nowadays being used at several radioactive beam facilities in the World, providing a powerful means to study the g.s. nuclear moments in the region far from the stability.

Electromagnetic moments provide useful information in nuclear structure physics.

As a recent work with polarized RI beam, preliminary result for the 33Al Q-moment has been presented.