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
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
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!
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