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TetraNuc Collaboration

TetraNuc Collaboration. In Search for the Tetrahedral Symmetry in the Actinides: A possible experimental proof through the ELMA Project. D. Curien IPHC-DRS Strasbourg Main collaborators for this talk : J. Dudek, K. Mazurek, H. Molique and L. Sengele.

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TetraNuc Collaboration

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  1. TetraNuc Collaboration Kazimierz Workshop 22-26 September 2010

  2. In Search for the Tetrahedral Symmetry in the Actinides: A possible experimental proof through the ELMA Project D. Curien IPHC-DRS Strasbourg Main collaborators for this talk : J. Dudek, K. Mazurek, H. Molique and L. Sengele Kazimierz Workshop 22-26 September 2010

  3. Combination of Group-Theory and Mean-Field formalism (J. Dudek, A. Gozdz and collaborators):effect on nuclear stability? • Rare-Earth: earliest experimental criteria • Explore the Actinides region • ELMA project: possible future experiments • Summary and Conclusions Kazimierz Workshop 22-26 September 2010

  4. Point Groups TetrahedralSymmetry Single Particle Energies Wood-Saxon (uni.) potential Neutron Proton 94 90 70 64 56 Full lines correspond to 4-fold degenerated orbitals consequence of large number of irreducible representations Observe huge gaps around Z=56,64,70 and N=90-94. They are comparable to the usual spherical gaps and often larger than the competing quadrupole shell gaps Kazimierz Workshop 22-26 September 2010

  5. Historical Earliest Criteria • The tetrahedral (a32) nuclei are predicted around the following new shell closures: (Zt , Nt ) = (32, 40, 56, 64, 70, 90, 112, 136) • Oriented object: rotational bands E ~ I(I+1) • Ideal static symmetry: Q2 [tet] = 0 • Surface modeled with odd-rank harmonics: Y [l=3] -> p=- • Look for negative parity rotational bands with vanishing intra-band E2-transitions (2006) • Question: what about “classic” a30 octupole symmetry? Kazimierz Workshop 22-26 September 2010

  6. Example: Rare-Earth Region Total Potential Energy a30 No minimum for usual Octupole deformation a32 a20 J. Dudek, K. Mazurek 2009 Clear low lying minima for Tetrahedral deformation a20 Kazimierz Workshop 22-26 September 2010

  7. Our point of view Kazimierz Workshop 22-26 September 2010

  8. First Candidate: JYFL and ILL exp. • ILL (n,g) results: • M. Jentschel et al. PRL 104, 222502 (2010) • 5- to 3- transition seen in single with extremely low intensity ~10-6 • T1/2 (5-)= 220 ps • Q2 ~ 7 b Equivalent to gsb • not a tetrahedral band following earliest criteria 15664Gd92 Doan Q.T. Phd Thesis, IPNL Vanishing E2’s Negative parity side band with odd-spins: known as a “vibrational“ octupole band Kp=1- with an even-spin partner Kazimierz Workshop 22-26 September 2010

  9. What Is The Usual Criteria ? • Fingerprints of the symmetry in molecular physics: branching ratios • In nuclear physics? That’s theultimate goal but still means a lot of work for theory Have a look at the complexity of analyzing the branching ratios ! Kazimierz Workshop 22-26 September 2010

  10. Other Point of View Self consistent mean field approach iThemba 160Yb exp. Kazimierz Workshop 22-26 September 2010

  11. So: What About Experiments Now? • Create a corpus of specific data with current best-instruments: • Rare-Earth: 156Dy Gammasphere (ANL), 156Gd GAMS (ILL) • Actinides: Orgam (IPNO), Jurogam2 (JYFL) • Develop specific instrument whenever requested: ELMA project T1/2 in Actinides Kazimierz Workshop 22-26 September 2010

  12. The Actinides: A More Promising Region? “magic numbers” N,Z=90-94,136-142 Elements of interest: thorium uranium plutonium • Tetrahedral minimum: • 500 keV above GS • significant barrier: 2.5 MeV • maximum effect of octahedral symmetry • Stronger stability than prolate/oblate/spherical shape coexistence Kazimierz Workshop 22-26 September 2010

  13. Previous Actinides Studies ofReflection-Asymmetric Shapes • Theoretical studies of (some) octupole bands: • Cranked RPA Hackman et al. 1998 240Pu & 248Cm • Collective model Minkov et al. 2006 staggering 224,226Ra &224,226Th • spdf IBA Zamfir et al. 2003-05 U,Pu & light actin. Z~88 • VMI model Lenis & Bonatsos 2006 226Ra &226Th • Alpha-particle model Shneidman et al. 2002 staggering • Pb core + exotic cluster model Buck et al. 2008 K>0 bands • Experimental evidence: • Butler, Cocks et al. 1999-2000 only even-even Rn, Ra & Th • But nothing is said on U & Pu isotopes Kazimierz Workshop 22-26 September 2010

  14. Octupole Degree of Freedom: a systematic from the levels energy • Difference in aligned angular momentum (from VMI) D ix= ix-- ix+ at a givenw • Two limits: • Permanent octupole deformation: i = RD ix= 0h • Octupole vibration: when the octupole phonon is aligned D ix= 3h K=0- Kazimierz Workshop 22-26 September 2010

  15. N ~ 134 3 “vibrators” Z = 86 0 “permanent” Z = 88 Z = 90 What about U & Pu? P. Butler Phys. Scripta T88, 7, 2000 Kazimierz Workshop 22-26 September 2010

  16. Uranium Isotopes:very special Hindrance E1’s 3*10-8 No E2’s B(E2)/B(E1) *106 0.4 0.4 0.4 1.3 236U(d,pn) multi-Coulex D. Ward 231Pa(p,2n) 231Pa(p,4n) 232Th(a,2n) 208Pb(22Ne,4n) P. Greenlees 230Th(a,2n) P. Zeyen et al. Z.Phys.A 2328,399 (1987): e-g coincidence Kazimierz Workshop 22-26 September 2010

  17. Differential alignment: Uranium Kazimierz Workshop 22-26 September 2010

  18. Differential alignment: Plutonium Kazimierz Workshop 22-26 September 2010

  19. Comparisons With Mean Fields Predictions 1 : a32 Uranium isotopes a20 232 226 228 234 236 230 Kazimierz Workshop 22-26 September 2010

  20. Comparisons With Mean Fields Predictions 2 : a32 Plutonium isotopes a20 240 242 244 Kazimierz Workshop 22-26 September 2010

  21. Comparisons With Mean Fields Predictions 3 : a32 Thorium isotopes a20 230 224 226 232 228 234 Kazimierz Workshop 22-26 September 2010

  22. Octupole: Permanent Def. versus Vib. a30 Thorium isotopes a20 224 222 228 226 232 230 Kazimierz Workshop 22-26 September 2010

  23. Synthesis of The ComparisonA Possible Tetra-Island ? Octupole permanent deformation Octupole vibration Tetrahedral deformation Kazimierz Workshop 22-26 September 2010

  24. Uranium Isotopes:an hypothesis on old measurements Octupole deformation  Tetrahedral shape  Octupole vibration ? 1998 Jurosphere P. Greenlees 1987 P. Zeyen e and 3 g detectors 1996 8 p D. Ward  More data requested ! Kazimierz Workshop 22-26 September 2010

  25. What Can Be Done Experimentally Nowadays? • Revisit the decay schemes to improve the branching ratio measurements: gg-e coincidences • Search for new negative parity bands where we think the tetrahedral candidates might come as a second excited band: e.g. multicoulex 236U • Measure the lifetime of the states of interest wherever possible to obtain the reduced transition probabilities  ELMA project (Electron for Lifetimes Measurements in Actinides) Kazimierz Workshop 22-26 September 2010

  26. How to Measure Lifetimesin Light U? • With gamma? impossible • Plunger : no recoil velocity with the a, p reactions • Fast timing: gating not possible above the states of interest • With conversion electrons? •  May Be!(and most probably the only possibility) 3-50 ps The Microwave Method Kazimierz Workshop 22-26 September 2010

  27. Goldring’s Microwave Setup Electromagnetic shutter-like device: selection of electrons according to their time of emission HF Beam chopper and beam sweeping cavity 1 2 3 DC very short bursts a, p Changing relative phase between the 2 cavities = modulating the electron energy in function of time  variable time-scale between the production of excited states and their decay via conversion electrons Kazimierz Workshop 22-26 September 2010

  28. Summary & Conclusions • Since the launch of the TetraNuc collaborations, 11 experiments have been accepted worldwide • The first important results have appeared this year in the Rare-Earth regions bringing some proof in contradiction with the simple historical criteria of the vanishing quadrupole moment for 156Gd • More crucial experimental results are expected soon with a plunger experiment at Gammasphere in 156Dy and new results from Coulex on 156Gd (LNL-India-Warsaw-Strasbourg) • Meanwhile, important progresses have been made in the more promising region of the Actinides that shows the existence of a possible island of tetrahedral nuclei. • This possibility is calling for the creation of a modern dedicated corpus of data • A possible way to realize this corpus has been formulated through the ELMA project Kazimierz Workshop 22-26 September 2010

  29. List of main TetraNuc collaborators D. Curien, J. Dudek, Ch. Beck, S. Courtin, O. Dorvaux, G. Duchêne, B. Gall, F. Haas, H. Molique, J. Piot, , J. RobinM. Rousseau, L. SengeleIPHC, Strasbourg D. Guinet, N. Redon,O.Stezowski, Q.D. Tuyen, A. VancraeyenestIPN, Lyon F. Azaiez, F. Ibrahim, C.Petrache, D. VerneyIPN, Orsay A. Astier, I. Deloncle, A. Korichi CSNSM, Orsay D.J. HartleyUS Naval Academy, Annapolis N.DubrayCEA, Bruyères-le-Châtel J F. Sharpey-Schafer iTHemba, Cape-Town Ch. Schmitt Ganil, Caen J. Gerl GSI, Darmstadt B. Lauss, J. Jentschel, W. UrbanILL,Grenoble P.T. Greenlees, P. Jones, R. Julin, et al. JYFL, Jyvaskyla P. Bednarczyk,B. Fornal, A. Maj, K. Mazurek, K. Zuber IFJ-PAN, Krakow T. Bhattacharjee, S. K. Basu et al.VECC, Kolkata G. de Angeliset al.INFN, Legnaro A. Gozdz, A. Dobrowolski - University of Lublin R.P. Singh, S. Muralithar, R. Kumar, et al. IUAC, New Delhi D. TonevBAS, Sofia L. Riedinger(and the US Gammasphere collaboration),N. SchunckUniversity of Tennessee J. Srebrny,M. ZielinskaSLCJ, Warsaw J. Dobaczewski, P. OlbratowskiWarsaw University Thank you! Kazimierz Workshop 22-26 September 2010

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