1. Octupole collectivity studied using radioactive-ion beams
Liam P. Gaffney
Oliver Lodge Laboratory, University of Liverpool, UK
Instituut voor Kern- en Stralingsfysica, KU Leuven, Belgium 1

2. Octupole Collectivity2λ
λ = Quadrupole
λ = Octupole
226Ra
Octupole correlations enhanced at magic numbers: 34, 56, 88, 134
Exotic regions of the Segré chart, so far inaccessible.
Radioactive Ion Beams are the key
144Ba
68Se
90Se
148,,150Nd
Schiff moment
CP violation
EDM
Odd-A
Talk by Peter Butler earlier this morning

3. Octupole Collectivity20 28 50 82
126
184
Microscopically...
Intruder orbitals of opposite parity and ∆J, ∆L = 3 close to the Fermi level 34 56 88
134 εF
220Rn and 224Ra lie near Z=88, N=134

4. Octupole Collectivity
Macroscopically...
Nuclei take on a “pear” shape
Reflection asymmetric
• β3-vibration
• Static β3-deformation
• Rigid β3-deformation...
Signatures...
Odd-even staggering, negative parity
Parity doublets in odd-A nuclei
Enhanced E1 transitions
Large E3 strength → =

5. Octupole Collectivity
Z = 88
N = 134
Z = 34
Z = 56
Rn (Z=86)?

6. Radon-220 and Radium-224 220Rn 224Ra
[ref] J.F.C. Cocks et al. Phys. Rev. Lett. 78 (1997) and Nucl. Phys. A 645 (1999)

7. Coulomb Excitation Sommerfeld parameter: “Safe” Coulex:
Projectile (Z1,A1)
Target (Z2,A2) b θ v
Sommerfeld parameter:
“Safe” Coulex:
Reduced matrix elements:

8. REX-ISOLDE UCx Isotope Separation On- Line D- Etector RIB E- Xperiment
Radioactive
Ion
Beam
1.4GeV protons
from PS Booster A D
Post-acceleration
Mass separation
in HRS C
Heated tungsten line (Ra)
Plasma ion source (Rn)
Ionised atoms diffuse out of target B
UCx 8

9. MINIBALL @ REX-ISOLDE 220Rn/224Ra beam @ ~2.83A.MeV Coulex target
~2mg/cm2 9

10. MINIBALL • Particle ID in a Double-Sided Si Strip Detector.
• Event by event Doppler correction.
• 17˚ < θlab < 54˚
• Array of HPGe of 8 triple clusters
• 6-fold segmentation for positioning
• ε > 7% for 1.3MeV γ-rays

11. Particle-gamma coincidences
Random
Prompt
Normalisation = tprompt
trandom

12. Analysis - 224Ra: Ni/Sn 60Ni target - 2.1mg/cm2
120Sn target - 2.0mg/cm2

13. Analysis - 220Rn: Ni/Sn 60Ni target - 2.1mg/cm2
120Sn target - 2.3mg/cm2

14. Analysis - 220Rn γ-γ
γ(697 keV)

15. Analysis - 220Rn: High/Low θ
High CoM θ
Low CoM θ

16. Analysis - 224Ra Gosia χ2 = 0.55 Total 55 data points
16 free matrix elements + 6 normalisation factors
“Experiment”
Number and type of data
Multi-nucleon transfer[1,2]
226Ra(58Ni,60Ni)224Ra
232Th(136Xe,128Te)224Ra
Alpha, alpha-prime[3]
226Ra(α,α’2n)224Ra
Alpha(beta)-decay[4]
228Th(224Fr) → α(β)
Branching ratios (1-, 3-, 5-, 7-, 2+γ)
-- 5
Delayed-coincidence[5,6]
Lifetimes (2+, 4+)
Cd/Sn high CoM range
23.9˚ < θlab < 40.3˚
γ-ray yield
Ni high CoM range
23.1˚ < θlab < 39.9˚
-- 10
Cd/Sn low CoM range
40.3˚ < θlab < 54.3˚
Ni low CoM range
39.3˚ < θlab < 53.2˚
-- 7
Total
55 data points
χ2 = 0.55
[1] Poynter et al., Phys. Lett. B 232, 447 (1989)
[2] J.F.C. Cocks et al., Nucl. Phys. A 645, 61 (1999)
[3] Marten-Tölle et al., Z. Phys. A 336, 27 (1990)
[4] W. Kurcewicz, et al., Nucl. Phys. A 289 (1977)
[5] W.R. Neal and H.W. Kraner, Phys. Rev. 137, B1164 (1965)
[6] H. Ton et al., Nucl. Phys. A 155, 235 (1970) 16

17. Results - 224Ra Awaiting publication Embargoed by Journal
• Consistent with rotational model
• Unstretched E3 matrix elements are non-zero. Rot-vib model predicts these vanish
• Coupled with level energy data, we observe a static octupole deformation in 224Ra 0+ 2+ 4+ 1- 3- 5-
3ℏ phonon

18. Analysis - 220Rn Gosia χ2 = 0.86 Total 34 data points
15 free matrix elements + 6 normalisation factors
“Experiment”
Number and type of data
Multi-nucleon transfer[1,2]
226Ra(58Ni,60Ni)224Ra
232Th(136Xe,128Te)224Ra
Alpha, alpha-prime[3]
226Ra(α,α’2n)224Ra
Alpha(beta)-decay[4]
228Th(224Fr) → α(β)
Branching ratios (1-, 5-, 7-)
-- 3
Delayed-coincidence[5,6]
Lifetimes (2+)
Cd/Sn/Ni high CoM range
22.1˚ < θlab < 37.8˚
γ-ray yield
Cd/Sn/Ni low CoM range
37.9˚ < θlab < 51.8˚
Total
34 data points
χ2 = 0.86
[1] Poynter et al., Phys. Lett. B 232, 447 (1989)
[2] J.F.C. Cocks et al., Nucl. Phys. A 645, 61 (1999)
[3] Marten-Tölle et al., Z. Phys. A 336, 27 (1990)
[4] W. Kurcewicz, et al., Nucl. Phys. A 289 (1977)
[5] W.R. Neal and H.W. Kraner, Phys. Rev. 137, B1164 (1965)
[6] H. Ton et al., Nucl. Phys. A 155, 235 (1970)

19. Results - 220Rn Awaiting publication Embargoed by Journal
• Consistent with rotational model.
• No information on unstretched E3.
• Larger data set required to determine if <1-||E3||2+> or <1-||E3||4+> vanish.
• Not definitive determination of collective mode, dynamic (vibrational) or static (rotational) from Q3 alone.
• δE and Δix implies a coupling of an octupole phonon to the even-spin rotational band.
• Magnitude of Q3 consistent with dynamic picture, similar to Q3(208Pb) and Q3(232Th)
• Dynamic collectivity in 220Rn
Awaiting publication
Embargoed by Journal

20. 220Rn - Vibrational?

21. Discussion and Interpretation
8 -8

22. Discussion and Interpretation

23. Comparison to theory Q2 Q3 Q1 Awaiting publication
• Cluster model [1] - Misses small Q1
- Q2 is consistently too low
- Q3 trend not observed
• Mean field, HFB with D1S or D1M [2]
- Predicts cancelation of Q1
- Differences in Q3 predictions
Awaiting publication
Embargoed by Journal Q2 Q3
[1] Shneidman, et al. (2003). Phys. Rev. C, 67(1), 14313
[2] Robledo, L. M., & Bertsch, G. F. (2011). Phys. Rev. C, 84(5), Q1

24. Summary & Outlook See talk by George O’Neill at 15.45 today
• Demonstrated sensitivity and ability to measure E3 matrix elements with Radioactive Ion Beams (RIBs).
• B(E3; 3- -> 0+) measured for the first time in Rn and only second measurement in Ra, both to ~10% precision.
• Experimental values rule out trend of cluster models.
• Exposes detailed differences in parameterisations of mean field calculations.
• Proposal for measurements in 222,226,228Ra and Ba region.
• Odd-mass nuclei key to atomic EDM measurements
See talk by George O’Neill at today

25. and the REX-ISOLDE and MINIBALL collaborations
Collaborators
T.E. Cocolios, J. Pakarinen, J.Cederkall, D. Voulot, F. Wernander
Th. Kröll, S. Bönig, C. Bauer, M. von Schmid
B. Bastin
T. Grahn, A. Herzan
A. Blazhev, M. Seidlitz, N. Warr, M. Albers, M. Pfeiffer, D. Radeck
M. Rudigier, P. Thöle
P. van Duppen, N. Bree, J. Diriken, N. Kesteloot
S. Sambi, K. Reynders
L. P. Gaffney, P. A. Butler, M. Scheck, D.T. Joss, S.V. Rigby
E. Kwan
T. Chupp
D. Cline, C.Y. Wu
M. Zielinska, P. Napiorkowski, M. Kowalczyk
D.G. Jenkins
CERN-ISOLDE, Switzerland
TU Darmstadt, Germany
Ganil, France
University of Jyväskylä, Finland
University of Köln, Germany
KU Leuven, Belgium
University of Liverpool, UK
Lawrence Livermore Laboratory, US
University of Michigan, US
University of Rochester, US
HIL University of Warsaw, Poland
University of York, UK
and the REX-ISOLDE and MINIBALL collaborations
Thank you!

26. Aside - Protons off...!
• Evidence of rapid exponential decay in beam rate after protons cease
• Comparison of direct production vs. alpha decay of parent (T1/2 = 3.66 days)

27. Radon-220 and Radium-224
220Rn
224Ra

28. Simulation - 224Ra

29. Simulation - 224Ra

30. Gosia Analysis Measured E3 matrix elements [e·fm3] Stretched:
Un-stretched:
Measured E2 matrix elements [e·fm2]
Transitional:
Diagonal:
[Ref] H. J. Wollersheim et al., Nucl. Phys. A 556, 261 (1993)

31. Gosia Analysis

32. Discussion and Interpretation - 224Ra