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

excited state Hyperfine splitting

laser photon

ionization potential

continuum

second step laser photon

ν2

ν1- + Δ ν

Laser spectroscopy

• Ion detection

ground state

excited state Hyperfine splitting

laser photon

ionization potential

continuum

second step laser photon

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

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

The Collinear Resonant Ionization Spectroscopy (CRIS) beamline

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)

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]

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]

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).

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

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

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

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

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

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