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

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Presentation on theme: "1 Liam P. Gaffney Oliver Lodge Laboratory, University of Liverpool, UK Instituut voor Kern- en Stralingsfysica, KU Leuven, Belgium Octupole collectivity."— Presentation transcript:

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

2 2 Octupole Collectivity λ = 2... Quadrupole λ = 3... Octupole 68 Se 90 Se 144 Ba 148,,150 Nd 226 Ra 2λ2λ 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 Schiff moment CP violation EDM Odd-A Talk by Peter Butler earlier this morning

3 3 Octupole Collectivity Microscopically... Intruder orbitals of opposite parity and ∆J, ∆L = 3 close to the Fermi level 220 Rn and 224 Ra lie near Z=88, N=134 εFεF

4 4 Octupole Collectivity Macroscopically... Nuclei take on a “pear” shape Reflection asymmetric β 3 -vibration Static β 3 -deformation Rigid β 3 -deformation... Signatures... Odd-even staggering, negative parity Parity doublets in odd-A nuclei Enhanced E1 transitions Large E3 strength → =

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

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

7 7 Coulomb Excitation Projectile (Z 1,A 1 ) Target (Z 2,A 2 ) b θ v Sommerfeld parameter: “Safe” Coulex: Reduced matrix elements:

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

9 9 REX-ISOLDE Rn/ 224 Ra ~2.83A.MeV Coulex target ~2mg/cm 2

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

11 11 Particle-gamma coincidences Prompt Random Normalisation = t prompt t random

12 12 Analysis Ra: Ni/Sn 60 Ni target - 2.1mg/cm Sn target - 2.0mg/cm 2

13 13 Analysis Rn: Ni/Sn 60 Ni target - 2.1mg/cm Sn target - 2.3mg/cm 2

14 14 Analysis Rn γ-γ γ(697 keV)

15 15 Analysis Rn: High/Low θ High CoM θ Low CoM θ

16 16 Analysis Ra Gosia 16 free matrix elements + 6 normalisation factors “Experiment”Number and type of data Multi-nucleon transfer [1,2] 226 Ra( 58 Ni, 60 Ni) 224 Ra 232 Th( 136 Xe, 128 Te) 224 Ra Alpha, alpha-prime [3] 226 Ra(α,α’2n) 224 Ra Alpha(beta)-decay [4] 228 Th( 224 Fr) → 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˚ < θ lab < 40.3˚ γ-ray yield Ni high CoM range 23.1˚ < θ lab < 39.9˚ γ-ray yield Cd/Sn low CoM range 40.3˚ < θ lab < 54.3˚ γ-ray yield Ni low CoM range 39.3˚ < θ lab < 53.2˚ γ-ray yield -- 7 Total55 data points [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) χ 2 =

17 17 Results Ra 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 224 Ra Awaiting publication Embargoed by Journal ℏ phonon

18 18 Analysis Rn Gosia 15 free matrix elements + 6 normalisation factors “Experiment”Number and type of data Multi-nucleon transfer [1,2] 226 Ra( 58 Ni, 60 Ni) 224 Ra 232 Th( 136 Xe, 128 Te) 224 Ra Alpha, alpha-prime [3] 226 Ra(α,α’2n) 224 Ra Alpha(beta)-decay [4] 228 Th( 224 Fr) → α(β) Branching ratios (1 -, 5 -, 7 - ) -- 3 Delayed-coincidence [5,6] Lifetimes (2 + ) -- 1 Cd/Sn/Ni high CoM range 22.1˚ < θ lab < 37.8˚ γ-ray yield Cd/Sn/Ni low CoM range 37.9˚ < θ lab < 51.8˚ γ-ray yield Total34 data points [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) χ 2 = 0.86

19 19 Results Rn Consistent with rotational model. No information on unstretched E3. Larger data set required to determine if or vanish. Not definitive determination of collective mode, dynamic (vibrational) or static (rotational) from Q 3 alone. δE and Δi x implies a coupling of an octupole phonon to the even-spin rotational band. Magnitude of Q 3 consistent with dynamic picture, similar to Q 3 ( 208 Pb) and Q 3 ( 232 Th) Dynamic collectivity in 220 Rn Awaiting publication Embargoed by Journal

20 Rn - Vibrational?

21 21 Discussion and Interpretation 8 -8

22 22 Discussion and Interpretation

23 23 Comparison to theory Q1Q1 Q2Q2 Q3Q3 Cluster model [ 1 ] - Misses small Q 1 - Q 2 is consistently too low - Q 3 trend not observed Mean field, HFB with D1S or D1M [ 2 ] - Predicts cancelation of Q 1 - Differences in Q 3 predictions [1] Shneidman, et al. (2003). Phys. Rev. C, 67(1), [2] Robledo, L. M., & Bertsch, G. F. (2011). Phys. Rev. C, 84(5), Awaiting publication Embargoed by Journal

24 24 Summary & Outlook See talk by George O’Neill at 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 222,226,228 Ra and Ba region. Odd-mass nuclei key to atomic EDM measurements

25 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 Thank you! and the REX-ISOLDE and MINIBALL collaborations

26 26 Aside - Protons off...! Evidence of rapid exponential decay in beam rate after protons cease Comparison of direct production vs. alpha decay of parent (T 1/2 = 3.66 days)

27 27 Radon-220 and Radium Rn 224 Ra

28 28 Simulation Ra

29 29 Simulation Ra

30 30 Gosia Analysis Measured E2 matrix elements [e·fm 2 ] Transitional: Diagonal: Measured E3 matrix elements [e·fm 3 ] Stretched: Un-stretched: [Ref] H. J. Wollersheim et al., Nucl. Phys. A 556, 261 (1993)

31 31 Gosia Analysis

32 32 Discussion and Interpretation Ra


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