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New techniques for probing nuclei shape around A=70

New techniques for probing nuclei shape around A=70. David Jenkins. Shape coexistence. Shape coexistence long-predicted for A=70 region Prolate and oblate shell gaps at N=Z=34 and 36 Oblate shapes are very rare Weak claim for oblate shape in 68 Se based on moment of inertia

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New techniques for probing nuclei shape around A=70

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  1. New techniques for probing nuclei shape around A=70 David Jenkins

  2. Shape coexistence • Shape coexistence long-predicted for A=70 region • Prolate and oblate shell gaps at N=Z=34 and 36 • Oblate shapes are very rare • Weak claim for oblate shape in 68Se based on moment of inertia • Weak claim for oblate shape in 72Kr based on comparison of B(E2) with theoretical results (A. Gade, PRL 95, 022502 (2005).) • Moral: Need new approaches to the problem!

  3. Reorientation in Coulomb excitation

  4. 70SeCO Molecular beam extraction (ISOL technique) • 1.4 GeV p-beam (900 ms) with Ib ~ 2.5 A • 1.5 x 1013 protons per pulse • Zr(IV)02 ISOLDE GPS target (500 – 600 A) • yield: 3 x 105 molecules of 70SeCO per C • MK7 plasma ion source  70SeCO+ molecular ions  ~ 6 x 105 ions transported to injection plate of REXTRAP each second (optimal running conditions)

  5. 70Se12C16O  98 a.m.u. Isobaric contaminants  A = 98 Break up 70SeCO inside EBISand charge breed up to a q = 19+ charge state (A/q ~ 3.68)  eliminates isobars! REX-ISOLDE   ~ 2.4%  Ib(70Se) ~ 1.4 x 104delivered to MB target

  6. 104Pd(70Se,70Se) @ 2.94 MeV/u “normal kinematics”

  7. Coulomb excitation of 70Se

  8. Conclusion: Oblate solution ruled out at 2-sigma level A remeasurement of 2+ lifetime could restrict this even further Preferred solution for 2+ state is weakly-deformed prolate Implies evolution from weakly to strongly deformed prolate as a function of spin A.M. Hurst et al. Phys. Rev. Lett. (in press) Where are the oblate shapes?

  9. Isobaric symmetry demands: If shape coexistence is present in Tz=1 nuclei e.g. 70Se then it must be present in the T=1 states in neighbouring odd-odd N=Z nuclei

  10. Odd-odd N=Z Fascinating laboratory for studying interplay of T=0 and T=1 states Very unusual low level density for odd-odd nuclei e.g. only 1 state below 1 MeV in 70Br Evidence for np-pairing in both low lying states and high spin rotational bands

  11. How to study odd-odd N=Z • Nuclei are difficult to produce without reactions close to 40Ca+40Ca at near-barrier energies • Production cross-sections are low (<1% of total cross-section) • Residues are too slow at focal plane of separator e.g. FMA to use ion chamber to identify Z • Most measurements done with neutron detectors + charge particle detectors to select e.g. pn or pn channel

  12. Recoil-decay tagging

  13. Recoil-beta tagging

  14. RITU+GREAT

  15. Test case: 74Rb

  16. natCa (36Ar, pn) 74Rb Ebeam = 103 MeV τ½ (74Rb) = 65 ms β+endpoint ~ 10 MeV σ~ 10 μb Proof-of-principle

  17. High energy positrons

  18. 1 10 MeV 3 10 MeV 6 10 MeV Varying the beta gate size

  19. Identification of 74Rb A.N. Steer, et al., NIM A565, 630 (2006)

  20. Intensity? 74Rb level scheme from RBT

  21. Unknown case:78Y • Nothing known about 78Y except 0+ superallowed decay and (5+) beta-decaying isomer • RBT technique applied using 40Ca(40Ca,pn)78Y reaction • Cross-section should be very similar to 74Rb • 90% of flux proceeds to low-lying isomer • Isomer is too long-lived for effective tagging

  22. Coulomb Energy Differences Extremely sensitive to nuclear structure effects: • Rotational alignment mechanism • Correlations of pairs of particles • Changes in deformation • The evolution of nuclear radii D.D. Warner et al., Nature Physics 2, 311 (2006)

  23. CEDs for A~70 CED(J)=Ex(J,T=1,Tz<)-Ex(J,T=1,Tz>) Difference in np and NN pairs gives CED rise of ~12 keV/J Uniform upward trend for deformed nuclei except: A=78 - flat A=70 - strongly down A=70 data from G. de Angelis, EPJ A12, 51 (2001) and D.G. Jenkins et al., PRC 65, 064307 (2002)

  24. 2=0.18 2=0.35 2=-0.3 2=0.35 Effect of shape change CED=-7 keV TRS calculations: T. Mylaeus et al., J. Phys. G 15, L135 (1989) CED=-75 keV R. Sahu et al., J. Phys. G 13, 603 (1987) Coulomb energies calculated after S. Larsson, Phys. Scri 8, 17 (1973).

  25. Conclusions • Reorientation is viable technique even at very low beam currents (104 /s) • Coulex supports weak prolate shape for 70Se 2+ • Recoil-beta-tagging: Powerful technique for study of odd-odd N=Z • Coulomb energy differences are sensitive to nuclear shape • CED for A=70 supports stretching of prolate shape as function of spin

  26. Plans for future measurements • Coulomb excitation: Extend to N=Z nuclei: 68Se and 72Kr • 72Kr is possible if we use B(E2) from MSU to constrain matrix elements • Recoil-beta-tagging: Search for Tz=-1 nuclei e.g.70Kr • Study mirror symmetry in A=71 i.e. 71Kr

  27. RBT Collaboration B.S. Nara Singh1, A.N. Steer1, D.G. Jenkins1, R. Wadsworth1, P. Davies1, R. Glover1, N.S. Pattabiraman1, T. Grahn2, P.T. Greenlees2, P. Jones2, R. Julin2, M. Leino2, M. Nyman2, J. Pakarinen2, P. Rahkila2, C. Scholey2, J. Sorri2, J. Uusitalo2, P.A. Butler3, M. Dimmock3, R. D. Herzberg3, D.T. Joss3, R.D. Page3, J. Thomson3, R. Lemmon4, J. Simpson4, B. Blank5, B. Cederwall6, B. Hadinia6, M. Sandzelius6 • Department of Physics, University of York, Heslington, York YO10 5DD, UK • Department of Physics, University of Jyväskylä, P.O. Box 35, FIN-40351, Jyväskylä, Finland • Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, UK • CCLRC Daresbury Laboratory, Keswick Lane, Warrington WA4 4AD, UK • Centre d’Etudes Nuclèaires de Bordeaux-Gradignan, F-33175 Gradignan Cedex, France • Royal Institute of Technology, Roslagstullsbacken 21, S-106 91 Stockholm, Sweden.

  28. REX-ISOLDE and Miniball collaborations: A.M. Hurst1, P.A. Butler1, D.G. Jenkins2, G.D. Jones1, E.S. Paul1, M. Petri1, C. Barton, A. Steer2, R. Wadsworth2, J.F. Smith3, T. Davinson4, I. Stefanescu5, J. Van de Walle5, O. Ivanov5, F. Ames6, J. Cederkall6,7, P. Delahaye6, S. Franchoo6, G. Georgiev6, U. Koster6, T. Sieber6, F. Wenander6, A. Ekstrom7, T. Czosnyka8, J. Iwanicki8, M. Zielinska8, H. Scheit9, J. Eberth10, N. Warr10, D. Weisshaar10, M. Pantea11, M. Munch12, S. Siem13, C. Sunde13, N. Syed13, A. Goergen14, E. Clement14, A. Buerger14. 1Department of Physics, University of Liverpool, UK2Department of Physics, University of York, UK3Department of Physics and Astronomy, University of Manchester, UK4Department of Physics and Astronomy, University of Edinburgh, UK5IKS, Catholic University of Leuven, Belgium6PH Division, CERN, Geneva, Switzerland7Department of Physics, University of Lund, Sweden8Heavy Ion Laboratory, University of Warsaw, Poland9MPI, University of Heidelberg, Germany10IKP, University of Cologne, Germany11IKP, Darmstadt Technical University, Germany12Department of Physics, Munich Technical University, Germany13Department of Physics, University of Oslo, Norway14CEA, Saclay, France

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