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Collinear resonance ionization spectroscopy of neutron rich 218m,219,229,231Fr isotopesIvan BudinčevićPhd student – nuclear moments group, IKS, KU LeuvenSupervisor: Gerda Neyens
ISOLDE Workshop, 27.11.2013
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Contents
• Physics motivation
• The CRIS experimental setup at ISOLDE
• Experimental results and discussion
• Conclusions
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Fr physical motivation
• 218,219Fr both exhibit alternating parity bands [1,2] which are generally associated with the presence of octupole deformations [3].
• The observed inversion of odd-even staggering of charge radii for 221-225Fr [4] has been associated with octupole deformations.
Neutron-rich Fr isotopes
[1] M. E. Debray et al., Phys. Rev. C 62, 024304 (2000), [2] C.F. Liang et al., Phys. Rev. C 44, 676 (1991), [3] R.K. Sheline Phys.Lett. 197B, 500 (1987), [4] A. Coc et al., Phys.Lett. 163B, 66 (1985)
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Alternating parity band 218Fr[1] M. E. Debray et al., Phys. Rev. C 62, 024304 (2000)
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Parity doublet band 219Fr
[2] C.F. Liang et al., Phys. Rev. C 44, 676 (1991)
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Laser spectroscopy
• Ion detection
ground state
excited state Hyperfine splitting
ν1
laser photon
ionization potential
continuum
second step laser photon
ν2
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Laser spectroscopy
• Ion detection
ground state
excited state Hyperfine splitting
laser photon
ionization potential
continuum
second step laser photon
ν2
ν1- + Δ ν
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Laser spectroscopy
• Ion detection
ground state
excited state Hyperfine splitting
laser photon
ionization potential
continuum
second step laser photon
ν2
ν1- - Δ ν
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Ion detection characteristics
• No losses due to solid angle coverage and scattered laser light - > higher detection efficiency compared to photon detection
• Ion beam transport efficiency is an important factor
• Neutralization efficiency (Charge Exchange)
• High vacuum is required ~ 10-8 – 10-9 mbar
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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The Collinear Resonant Ionization Spectroscopy (CRIS) beamline
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Laser system
422nm
1064nm
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Fr experimental results – reference isotopes
Fr ionization scheme
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Fr experimental results – 218mFr, 219Fr
T1/2(218mFr) = 0.022(5) s [5], scan made in 44min
T1/2(219Fr) = 0.0267(6) s [5], scan made in 33min
[5] G.T. Ewan et al., Nucl. Phys. A380 (1982) 423
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218mFr half-life
218Fr alpha-particle energy spectrum
Half-life determination
[6] K. M. Lynch and K. Flanagan, Laser assisted nuclear decay spectroscopy: A new method for studying neutron-deficient francium, Ph.D. thesis, Manchester U. (2013)
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Fr experimental results – 229Fr, 231Fr
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Characteristics of the region of reflection asymmetry – octupole deformations
• Quadrupole – octupole shapes for β2 = 0.6, β3µ = 0.35, taken from [7] Butler Rev.Mod. Phys. 68 (1996) 349
µ = 0 µ = 1 µ = 2 µ = 3
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Characteristics of the region of reflection asymmetry – spectroscopic properties
• Parity doublet bands
• Charge radii/isotope shifts
• Ground state spins and magnetic moments
• Coriolis matrix elements
• Spectroscopic factors
• Enhanced E1 transition probabilities
[3] R.K. Sheline Phys.Lett. 197B, 500 (1987)
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Characteristics of the region of reflection asymmetry – spectroscopic properties
• Parity doublet bands
• Charge radii/isotope shifts
• Ground state spins and magnetic moments
• Coriolis matrix elements
• Spectroscopic factors
• Enhanced E1 transition probabilities
[3] R.K. Sheline Phys.Lett. 197B, 500 (1987)
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Relative mean-square charge radii
[4] A. Coc et al., Phys.Lett. 163B, 66 (1985), [8] K. Wendt et al., Z. Phys. D 4, 227 (1987), [9] V.A. Dzuba et al., Phys.Rev. A 72, 022503 (2005), [10] L.W. Wansbeek et al., Phys.Rev. C 86, 015503 (2012)
( 1),126 ( 1),126,126( ; ) ( 1)
2
N NN ND N
• The large theoretical errors stem from the calculated uncertainties for the Field and mass shift constants for Ra [9,10]
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Relative mean-square charge radii
[4] A. Coc et al., Phys.Lett. 163B, 66 (1985). [8] K. Wendt et al., Z. Phys. D 4, 227 (1987), [11] A. Coc et al., Nuclear Physics A468 (1987) 1
Taken from [9]
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Relative mean-square charge radii
• OES effect of pairing on the collective potential .
• Normal OES – smaller <r2> for odd N nuclei compared to the average of their even N neighbors.
[12] S. Ahmad et al., Nuc. Phys. A 483,244 (1988).
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Relative mean-square charge radii
• Inverted odd even staggering for 221-225Fr (N=135-138) and 221-226Ra (N=133-138)
[4] A. Coc et al., Phys.Lett. 163B, 66 (1985). [8] K. Wendt et al., Z. Phys. D 4, 227 (1987), [11] A. Coc et al., Nuclear Physics A468 (1987) 1
• Our results for δν(219,229Fr) will add the points for D(N; δν) (220,228Fr) (N=133,141) to this plot
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220-228 Fr interpretations from literature
[13] RK Sheline. Octupole deformation in odd-odd nuclei. Phys. Rev. C, 37(1)1988, [14] C. Ekstrom et al., Phys. Scr. 34:624-633,1986.[15] W. Kurcewicz, et al., Nuc. Phys A, 539(3)1992. [16] D.G. Burke, W Nuc. Phys.A,612(1)1997. [17] W. Kurcewicz et al., Nucl. Phys. A, 621(4)1997.
• The spin sequence for 220,222,224,226,228Fr was reproduced by [13] including octupole deformations.
• Magnetic dipole and electric quadrupole moments of 224,226,228Fr were qualitatively well reproduced by [14] without octupole deformations
• 223Fr was studied by [15] and they concluded the experimental data agreed with the theoretical predictions of a reflection asymmetric rotor model.
• [16] concluded octupole correlations do play a role in 225 Fr, but there is no stable deformation.
• 227Fr is considered to be a transitional nucleus [17]
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Magnetic dipole moments and nuclear g factors
d 3/2
s 1/2
Z = 82
h 9/2
f 7/2
i 13/2
protons
d 3/2
s 1/2
Z = 82
h 9/2
f 7/2
i 13/2
particle-hole excitations
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Magnetic dipole moments and nuclear g factors
2d 3/2
3s 1/2
Z = 82
1h 9/2
1f 7/2
2i 13/2
protons
2h 11/2
3p 1/2
N = 126
2g 9/2
1i 11/2
1j 15/2
neutrons
221Fr -> N = 134
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Magnetic dipole moments and nuclear g factors
d 3/2
s 1/2
Z = 82
h 9/2
f 7/2
i 13/2
particle-hole excitations
2h 11/2
3p 1/2
N = 126
2g 9/2
1i 11/2
1j 15/2
neutrons
227Fr -> N = 140
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Conclusions
• Collinear resonance ionization spectroscopy was used to measure the hyperfine structure of the 218m,219,229,231Fr isotopes.
• The extracted magnetic dipole moments and relative mean-square charge radii will provide information about the nuclear structure of these isotopes, lying on the borders of the region of reflection asymmetry.
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Conclusions
• The isotope shifts will show if these isotopes do exhibit inverted odd-even staggering, which has been associated with the presence of reflection-asymmetric nuclear shapes.
• The magnetic dipole moments will provide information of the orbital occupancy of the valence nucleons.
• Information about the nuclear spin for 229,231Fr may be attained.
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THANK YOU FOR YOUR ATTENTION
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Extra slides
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Odd-even staggering Y factor
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Nuclemon
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Nuclemon
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Quadrupole octupole shapes
• where αλμ are deformation parameters, c(α) is determined from the volume conservation condition and R0=roA1/3
α30=β30 ; α3-m=(-1)m α3m=β3m/2; β3m=0.35
max*
02
( ) ( ) 1 ( )R c R Y
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Conditions for static octupole deformations
Butler Rev.Mod. Phys. 68 (1996) 349
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Parity mixing
• The pairing plus multipole hamiltonian
• where the first term on the right-hand side is the spherical shell-model potential, the second term represents a long-range separable multipole-multipole force generating the collective motion, Hpair is the pairing Hamiltonian, and j stands for the set of quantum numbers (n, l ,j).
• Qλµ is the multiple operator
• and fλ(r) is the radial form factor
'12j j j pair
j
e c c k Q Q H
''
( ) ( ) ' j jjj
Q j f r Y j c c
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Parity mixing
• A coupling between single-particle states of opposite parity is produced by the octupole-octupole (λ=3) residual interaction.
• The necessary condition for the presence of low-energy octupole collectivity is the existence, near the Fermi level, of pairs of orbitals strongly coupled by the octupole interaction.
• For normally deformed systems the condition for strong octupole coupling is satisfied for particle numbers associated with the maximum ΔN=1 interaction between the intruder subshell (l ,j) and the normal-parity subshell (l - 3, j - 3)
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Parity mixing
Nuclear spherical single particle levels with the most important octupole couplings highlighted