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

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

Octupole Collectivity 20 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

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 → =

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

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)

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

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

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

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

Particle-gamma coincidences Random Prompt Normalisation = tprompt trandom

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

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

Analysis - 220Rn γ-γ γ(697 keV)

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

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+) -- 2 Cd/Sn high CoM range 23.9˚ < θlab < 40.3˚ γ-ray yield -- 8 + 7 Ni high CoM range 23.1˚ < θlab < 39.9˚ -- 10 Cd/Sn low CoM range 40.3˚ < θlab < 54.3˚ -- 8 + 8 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

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

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+) -- 1 Cd/Sn/Ni high CoM range 22.1˚ < θlab < 37.8˚ γ-ray yield -- 2 + 8 + 5 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)

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

220Rn - Vibrational?

Discussion and Interpretation 8 -8

Discussion and Interpretation

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), 54302. Q1

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 15.45 today

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!

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)

Radon-220 and Radium-224 220Rn 224Ra

Simulation - 224Ra

Simulation - 224Ra

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)

Gosia Analysis

Discussion and Interpretation - 224Ra