β-NMR/NQR measurements at the LISE fragment separator in GANIL

Neutron-rich Al at the border of the island of inversion

20th Colloque GANIL, October 2017

Hanne Heylen

Introductionβ-detected Nuclear Magnetic Resonance (β-NMR) at LISE-GANIL

… for nuclear moment measurements - g-factor (= magnetic dipole moment μ/I) - Electric quadrupole moment Qs

… to study nuclear structure - Valence proton/neutron configuration - Deformation

… of isomer in 34Al near the island of inversion at N = 20

β-NMR/NQR

• Spin-polarization - Unequal population of m-states - β-decay is anisotropic in space

(Nup ≠ Ndown) - A = (Nup - Ndown)/(Nup + Ndown) ∝ degree of polarization

m = -1 m = 0 m = 1

Pop

ulat

ion

β-NMR/NQRβ-NMR β-NQR

B + electric field gradient Vzz

External magnetic field B

m=1

m=0

m=-1

• Implanted in crystal (cubic crystal structure) - νL∝ |g|.B

• g-factor measurement - RF magnetic field with frequency νRF - νRF = νL → Equalize m-state population

→ Polarization = 0 - Detect change in asymmetry when

polarization is resonantly destroyed

β-NMR/NQRβ-NMR β-NQR

External magnetic field B

B + electric field gradient Vzz

• Implanted in crystal (axially symmetric electric field gradient) - νL∝ |g|.B - νQ∝ |Qs|.Vzz

• Non-equidistant splitting - 2I (correlated) frequencies simultaneously

β-NMR/NQR at LISE-GANIL

Momentum selection slits

Primary beam at 2∘

• Spin-polarization in reactions at LISE-GANIL

a) Projectile-fragmentation b ) Pick-up

Pola

rizat

ion

pf,x- pppp

Yie

ld

pf,x- pppp

0

Pola

rizat

ion

pf,x- pppp

Yie

ld

pf,x- pppp

0

β-NMR/NQR at LISE-GANIL

Why use β-NMR at LISE-GANIL?

β-NMR

What? g, Qs (2 spectra)

Lifetime? β-decaying ms - s

Specifics Implantation crystal (Implantation position, relaxation time, …)

Why use β-NMR at LISE-GANIL?

β-NMR Laser spectroscopy

What? g, Qs (2 spectra) g, Qs, I, δ<r2>(1 spectrum)

Lifetime? β-decaying ms - s Stable down to few ms

Specifics Implantation crystal (Implantation position, relaxation time, …)

Excitation scheme (Size of A and B, available laser freq.)

Why use β-NMR at LISE-GANIL?

β-NMR Laser spectroscopy

What? g, Qs (2 spectra) g, Qs, I, δ<r2>(1 spectrum)

Lifetime? β-decaying ms - s Stable down to few ms

Specifics Implantation crystal (Implantation position, relaxation time, …)

Excitation scheme (Size of A and B, available laser freq.)

LISE-GANIL ISOLDE

Polarization In reactions (Universal, few percent)

Laser induced (Polarization scheme, up to 100%)

Available beams

Challenging, but for specific cases best/only (?) choice!

8

20

28

50

8

20

28

ResultsSpin-orientation at LISE-GANIL

• D. Borremans, PRC 66 (2002) • K. Turzó, PRC 73 (2006)

Island of inversion around N = 2031-34Al:

• D. Borremans, PLB 537 (2002) • P. Himpe, PLB 643 (2006) • P. Himpe, PLB 658 (2008) • M. De Rydt, PLB 678 (2009) • H. Heylen, PRC 94 (2016) • Z. Xu, in preparation

35Si: • G. Neyens, EPJ 150 (2007)

Reduced Z = 16 and N = 28 shell gaps44Cl:

• M. De Rydt, PRC 81 (2010)

Commissioning of new set-up17,18N:

• M. De Rydt, PRC 80 (2009) • M. De Rydt, NIM A 612 (2009)

Island of inversion around N = 20

• Transitional nuclei are still challenging! - Subtle balance between quadrupole correlations and stabilizing shell gaps

30F

9

10

11

12

13

14

18 19 20 21 2217 N

Z

29Mg

30Mg

31Mg

32Mg

33Mg

34Mg

30Al

31Al

32Al

33Al

34Al

35Al

31Si

32Si

33Si

34Si

35Si

36Si

28Na

29Na

30Na

31Na

32Na

33Na

27Ne

28Ne

29Ne

30Ne

32Ne

26F

27F

28F

29F

31F

Normal

Unbound

Halo

Unknown31Ne

Transitional

Intruder

Intruder -1p-1hh

Tentative

1v4-

N = 20

d5/2

d3/2 s1/2

Z = 20 f7/2

p3/2

Normal sd-configuration

N = 20

d5/2

d3/2 s1/2

Z = 20 f7/2

p3/2

Intruder (2p-2h) configuration

34Si 32Mg

The 1+ intruder isomer in 34Al (N = 21)

• Proposed 1p-1h intruder [Rotaru, PRL 109 (2012)] - Isomer at 47 keV above gs [Lica, PRC 95 (2017)] - Verify configuration/purity via g-factor - Deformation due to 1p-1h excitations?

Exp. SDPF-M SDPF-U-MIX

g-factor 32Al 1.9516(22) 1.83 1.80 34mAl ? 1.73 1.76

Qs (mb) 32Al 24(2) 30 27 34mAl ? 43 44

x0.95

x1.5

g-factor: Himpe, PLB 643, 257 (2006); Qs: Kameda., PLB 647, 93 (2007)

SDPF-M (Tokyo): PRC 60, 054315 (1999) SDPF-U-MIX (Strasbourg): PRC 90, 014302 (2014)

The exotic 1+ isomer in 34Al

32Al

30Mg

31Mg

29Na

Time of flight

Ene

rgy

loss

in E

2D6

Time of flight

34Al

32Mg

36Si35Si

33Al

β-spectrum

β-spectrum Challenges• 600 34Al/s (20x less than 32Al)

- Only ~30% 1+

• Large background of gs + daughter β’s

- Reduction of asymmetry by factor of 9

• Preparation - Improved β-detection

efficiency by factor of 4 (R. Garcia Ruiz)

- Optimize on 32Al

• Max. 3.5 eµA 36S16+, 77.5 MeV/A on 1mm 9Be target + 1mm 9Be wedge

• Purity ~80%

β-NMR on 1+ isomer in 34Al

Sign of polarization

Focus on resonance

(add common points in 3

scan regions)

g(34mAl)/g(32Al) ~ 0.9

Z. Xu, H. Heylen et al., in preparation

24h, 3.5σ

17h, 2.8σ

β-NMR on 1+ isomer in 34Al

g(34mAl)/g(32Al) ~ 0.9

→ Dominantly 1p-1h (little mixing with 3p-3h) → Good agreement with theory

Exp. SDPF-M SDPF-U-MIX

g-factor 32Al 1.9516(22) 1.83 1.80 34mAl ? 1.73 1.76

Qs (mb) 32Al 24(2) 30 27 34mAl ? 43 44

Exp. SDPF-M SDPF-U-MIX

g-factor 32Al 1.9516(22) 1.83 1.80 34mAl ? 1.73 1.76

Qs (mb) 32Al 24(2) 30 27 34mAl ? 43 44

17h, 2.8σ

24h, 3.5σ

Z. Xu, H. Heylen et al., in preparation

β-NMR on 1+ isomer in 34Al

β-NQR on 1+ isomer in 34Al

Q(34mAl)/Q(32Al) ~ 1.5

Same FWHM

Z. Xu, H. Heylen et al., in preparation

Conclusions

• First measurement of nuclear moments of 34mAl

• Last β-NMR campaign at GANIL? - Successful program in last 15 years - Challenging technique, but allows unique studies (e.g. 34mAl) - New cases require sufficient preparatory beam time!

CollaborationKU Leuven GANIL RIKEN Tokyo Tech University of Tokyo University of Athens CEA/DAM/DIF