Octupole collectivity studied using radioactive-ion beams

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

2. 2λ Odd-A EDM Schiff moment CP violation Octupole Collectivity λ = 2 ... Quadrupole λ = 3 ... 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 Talk by Peter Butler earlier this morning

3. 184 134 88 126 εF 56 82 34 50 28 20 Octupole Collectivity Microscopically... Intruder orbitals of opposite parity and ∆J, ∆L = 3 close to the Fermi level 220Rn and 224Ra lie near Z=88, N=134

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

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

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

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

8. D Post-acceleration 1.4GeV protons from PS Booster C A Mass separation in HRS Heated tungsten line (Ra) Plasma ion source (Rn) Ionised atoms diffuse out of target B REX-ISOLDE RIB E- Xperiment Radioactive Ion Beam Isotope Separation On- Line D- Etector 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. Prompt Random Particle-gamma coincidences • 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 16 free matrix elements + 6 normalisation factors 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. 5- 3- 4+ 1- 3ℏ phonon Awaiting publication Embargoed by Journal 2+ 0+ Results - 224Ra • 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

18. Analysis - 220Rn Gosia 15 free matrix elements + 6 normalisation factors 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. Awaiting publication Embargoed by Journal Results - 220Rn • 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

20. 220Rn - Vibrational?

21. Discussion and Interpretation 8 -8

22. Discussion and Interpretation

23. Q1 Q2 Q3 Comparison to theory Awaiting publication Embargoed by Journal • 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 [1] Shneidman, et al. (2003). Phys. Rev. C, 67(1), 14313 [2] Robledo, L. M., & Bertsch, G. F. (2011). Phys. Rev. C, 84(5), 54302.

24. Summary & Outlook • 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 15.45 today

25. 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. 224Ra 220Rn Radon-220 and Radium-224

28. Simulation - 224Ra

29. Simulation - 224Ra

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

31. Gosia Analysis

32. Discussion and Interpretation - 224Ra