collinear resonance ionization spectroscopy of neutron rich 218m,219,229,231 fr isotopes

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

Contents

• Physics motivation

• The CRIS experimental setup at ISOLDE

• Experimental results and discussion

• Conclusions

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)

Alternating parity band 218Fr[1] M. E. Debray et al., Phys. Rev. C 62, 024304 (2000)

Parity doublet band 219Fr

[2] C.F. Liang et al., Phys. Rev. C 44, 676 (1991)

Laser spectroscopy

• Ion detection

ground state

excited state Hyperfine splitting

ν1

laser photon

ionization potential

continuum

second step laser photon

ν2

Laser spectroscopy

• Ion detection

ground state


laser photon


continuum


ν2

ν1- + Δ ν

Laser spectroscopy

• Ion detection

ground state


laser photon


continuum


ν2

ν1- - Δ ν

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

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

Laser system

422nm

1064nm

Fr experimental results – reference isotopes

Fr ionization scheme

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

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)

Fr experimental results – 229Fr, 231Fr

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

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)

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]


[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]


• 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).


• 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

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]

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


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


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

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.

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.

THANK YOU FOR YOUR ATTENTION

Extra slides

Odd-even staggering Y factor

Nuclemon

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

Conditions for static octupole deformations

Butler Rev.Mod. Phys. 68 (1996) 349

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

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)

Parity mixing

Nuclear spherical single particle levels with the most important octupole couplings highlighted

collinear resonance ionization spectroscopy of neutron rich 218m,219,229,231 fr isotopes

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