Tetra Nuc Collaboration D Curien Kazimierz Workshop 22

Tetra. Nuc Collaboration D. Curien Kazimierz Workshop 22 -26 September 2010 1

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 D. Curien Kazimierz Workshop 22 -26 September 2010 2

• 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 D. Curien Kazimierz Workshop 22 -26 September 2010 3

Point Groups Tetrahedral Symmetry Proton Single Particle Energies Neutron Wood-Saxon (uni. ) potential 90 70 94 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 D. Curien Kazimierz Workshop 22 -26 September 2010 4

Historical Earliest Criteria • The tetrahedral (a 32) nuclei are predicted around the following new shell closures: (Zt , Nt ) = (32, 40, 56, 64, 70, 90, 112, 136) • • • Oriented object: rotational bands Ideal static symmetry: E ~ I(I+1) Q 2 [tet] = 0 Surface modeled with odd-rank harmonics: Y [l=3] -> p=- Ø Look for negative parity rotational bands with vanishing intraband E 2 -transitions (2006) Ø Question: what about “classic” a 30 octupole symmetry? D. Curien Kazimierz Workshop 22 -26 September 2010 5

Example: Rare-Earth Region Total Potential Energy a 30 No minimum for usual Octupole deformation a 20 a 32 J. Dudek, K. Mazurek 2009 Clear low lying minima for Tetrahedral deformation a 20 D. Curien Kazimierz Workshop 22 -26 September 2010 6

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

First Candidate: JYFL and ILL exp. 156 Gd 64 92 Doan Q. T. Phd Thesis, IPNL Vanishing E 2’s 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 • T 1/2 (5 -)= 220 ps Ø Q 2 ~ 7 b Equivalent to gsb Ø not a tetrahedral band following earliest criteria Negative parity side band with odd-spins: known as a “vibrational“ octupole band Kp=1 - with an even-spin partner D. Curien Kazimierz Workshop 22 -26 September 2010 8

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

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

So: What About Experiments Now? • Create a corpus of specific data with current bestinstruments: – Rare-Earth: 156 Dy Gammasphere (ANL), 156 Gd GAMS (ILL) – Actinides: Orgam (IPNO), Jurogam 2 (JYFL) • Develop specific instrument whenever requested: ELMA project T 1/2 in Actinides D. Curien Kazimierz Workshop 22 -26 September 2010 11

The Actinides: A More Promising Region? “magic numbers” N, Z=90 -94, 136 -142 Elements of interest: thorium uranium plutonium Tetrahedral minimum: • 500 ke. V above GS • significant barrier: 2. 5 Me. V • maximum effect of octahedral symmetry Stronger stability than prolate/oblate/spherical shape coexistence D. Curien Kazimierz Workshop 22 -26 September 2010 12

Previous Actinides Studies of Reflection-Asymmetric Shapes • Theoretical studies of (some) octupole bands: – – – 240 Pu & 248 Cm Cranked RPA Hackman et al. 1998 Collective model Minkov et al. 2006 staggering 224, 226 Ra & 224, 226 Th spdf IBA Zamfir et al. 2003 -05 U, Pu & light actin. Z~88 226 Ra & 226 Th VMI model Lenis & Bonatsos 2006 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 D. Curien Kazimierz Workshop 22 -26 September 2010 13

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

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

Uranium Isotopes: very special Hindrance E 1’s 3*10 -8 No E 2’s B(E 2)/B(E 1) *106 0. 4 1. 3 208 Pb(22 Ne, 4 n) P. Greenlees ) 231 Pa(p, 4 n) ) 231 Pa(p, 2 n) ) 230 Th(a, 2 n) ) 232 Th(a, 2 n) ) 236 U(d, pn) ) multi-Coulex D. Ward P. Zeyen et al. Z. Phys. A 2328, 399 (1987): e-g coincidence D. Curien Kazimierz Workshop 22 -26 September 2010 16

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

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

Comparisons With Mean Fields Predictions 1 : a 32 Uranium isotopes 226 D. Curien a 20 232 228 234 230 236 Kazimierz Workshop 22 -26 September 2010 19

Comparisons With Mean Fields Predictions 2 : a 32 Plutonium isotopes 240 a 20 242 244 D. Curien Kazimierz Workshop 22 -26 September 2010 20

Comparisons With Mean Fields Predictions 3 : a 32 Thorium isotopes a 20 D. Curien 224 230 226 232 228 234 Kazimierz Workshop 22 -26 September 2010 21

Octupole: Permanent Def. versus Vib. a 30 Thorium isotopes a 20 D. Curien 222 224 226 228 230 232 Kazimierz Workshop 22 -26 September 2010 22

Synthesis of The Comparison A Possible Tetra-Island ? Z/N 132 134 136 138 140 Pu 228 240 242 244 U 226 228 230 232 Th 222 224 226 228 230 Ra 220 222 224 226 228 Rn 220 222 Octupole permanent deformation D. Curien Tetrahedral deformation Kazimierz Workshop 22 -26 September 2010 142 144 146 234 236 238 232 234 Octupole vibration 23

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

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 236 U • Measure the lifetime of the states of interest wherever possible to obtain the reduced transition probabilities ELMA project D. Curien (Electron for Lifetimes Measurements in Actinides) Kazimierz Workshop 22 -26 September 2010 25

How to Measure Lifetimes in 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) The Microwave Method D. Curien 3 -50 ps Kazimierz Workshop 22 -26 September 2010 26

Goldring’s Microwave Setup HF Beam chopper and beam sweeping cavity 1 2 Electromagnetic shutter-like device: selection of electrons according to their time of emission 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 D. Curien Kazimierz Workshop 22 -26 September 2010 27

Summary & Conclusions • Since the launch of the Tetra. Nuc 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 156 Gd • More crucial experimental results are expected soon with a plunger experiment at Gammasphere in 156 Dy and new results from Coulex on 156 Gd (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 D. Curien Kazimierz Workshop 22 -26 September 2010 28

List of main Tetra. Nuc collaborators D. Curien, J. Dudek, Ch. Beck, S. Courtin, O. Dorvaux, G. Duchêne, B. Gall, F. Haas, H. Molique, J. Piot, , J. Robin M. Rousseau, L. Sengele IPHC, Strasbourg D. Guinet, N. Redon, O. Stezowski, Q. D. Tuyen, A. Vancraeyenest IPN, Lyon F. Azaiez, F. Ibrahim, C. Petrache, D. Verney IPN, Orsay A. Astier, I. Deloncle, A. Korichi CSNSM, Orsay D. J. Hartley US Naval Academy, Annapolis N. Dubray CEA, Bruyères-le-Châtel J F. Sharpey-Schafer i. THemba, Cape-Town Ch. Schmitt Ganil, Caen J. Gerl GSI, Darmstadt B. Lauss, J. Jentschel, W. Urban ILL, 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 Angelis et al. INFN, Legnaro A. Gozdz, A. Dobrowolski University of Lublin R. P. Singh, S. Muralithar, R. Kumar, et al. IUAC, New Delhi D. Tonev BAS, Sofia L. Riedinger (and the US Gammasphere collaboration), N. Schunck University of Tennessee J. Srebrny, M. Zielinska SLCJ, Warsaw J. Dobaczewski, P. Olbratowski Warsaw University Thank you! D. Curien Kazimierz Workshop 22 -26 September 2010 29