TetraNuc Collaboration

D. CurienD. Curien Kazimierz Workshop 22-26 September 2010Kazimierz Workshop 22-26 September 2010 11

TetraNuc CollaborationTetraNuc Collaboration


In Search for the Tetrahedral In Search for the Tetrahedral Symmetry Symmetry

in the Actinides: in the Actinides: A possible experimental proof throughA possible experimental proof through

the ELMA Projectthe ELMA Project

D. CurienD. Curien IPHC-DRS IPHC-DRSStrasbourgStrasbourg

Main collaborators for this talk : J. Dudek, K. Mazurek, H. Molique and L. Sengele Main collaborators for this talk : J. Dudek, K. Mazurek, H. Molique and L. Sengele


• Combination of Group-Theory and Mean-Field Combination of Group-Theory and Mean-Field

formalism (formalism (J. Dudek, J. Dudek, A. Gozdz A. Gozdz and collaborators): and collaborators):

effect on nuclear stability?effect on nuclear stability?

• Rare-Earth: earliest experimental criteriaRare-Earth: earliest experimental criteria

• Explore the Actinides regionExplore the Actinides region

• ELMA projectELMA project : possible future experiments: possible future experiments

• Summary and ConclusionsSummary and Conclusions


Point Groups TetrahedralPoint Groups Tetrahedral SymmetrySymmetry

Full lines correspond toFull lines correspond to 4-fold degenerated orbitals 4-fold degenerated orbitals consequence of large number of irreducible representationsconsequence of large number of irreducible representations

Observe Observe huge gapshuge gaps around Z= around Z=56,64,7056,64,70 and N= and N=90-94.90-94. They are comparable to the usual spherical gaps and oftenThey are comparable to the usual spherical gaps and often

larger than the competing quadrupole shell gapslarger than the competing quadrupole shell gaps

ProtoProtonn

NeutroNeutronn

70

56

64

9490

Single Particle EnergiesSingle Particle Energies Wood-Saxon (uni.) potentialWood-Saxon (uni.) potential


Historical Earliest Criteria Historical Earliest Criteria

• The tetrahedral (The tetrahedral (3232) ) nuclei are predicted nuclei are predicted aroundaround the the

following new shell closures:following new shell closures:

(Z(Zt t , N, Nt t ) = (32, 40, 56, ) = (32, 40, 56, 6464, 70, , 70, 9090, 112, 136), 112, 136)

• Oriented object: Oriented object: rotational bands rotational bands E ~ I(I+1)E ~ I(I+1)

• Ideal static symmetry: Ideal static symmetry: QQ2 2 [tet] [tet] = 0= 0

• Surface modeled with odd-rank harmonics: Surface modeled with odd-rank harmonics: Y [Y [=3] =3]

-> -> =-=-

Look for negative parity rotational bands with vanishing Look for negative parity rotational bands with vanishing intra-band E2-transitions (2006)intra-band E2-transitions (2006)

Question:Question: what about “classic” what about “classic” 3030 octupole symmetry? octupole symmetry?


Example: Rare-Earth RegionExample: Rare-Earth Region

20

20

32

30

No minimum for usualNo minimum for usualOctupole deformationOctupole deformation

Clear low lying minima forClear low lying minima forTetrahedral deformationTetrahedral deformation

J. Dudek, K. Mazurek 2009J. Dudek, K. Mazurek 2009

Total Potential EnergyTotal Potential Energy


Our point of viewOur point of view


First Candidate: First Candidate: JYFL and ILL exp.JYFL and ILL exp.

Negative parity side band with odd-spins: Negative parity side band with odd-spins: known as a known as a “vibrational“ octupole band “vibrational“ octupole band KK=1-=1- with an even-spin with an even-spin

partnerpartner

Vanishing E2’s

1561566464GdGd9292

Doan Q.T. Phd Thesis, IPNLDoan Q.T. Phd Thesis, IPNL ILL (n,ILL (n,) results:) results:M. Jentschel et al. M. Jentschel et al. PRL

104, 222502 (2010)

• 5- to 3- transition 5- to 3- transition seen seen in singlein single with with extremely low extremely low intensity ~10intensity ~10-6-6

• TT1/2 1/2 (5-)= 220 ps(5-)= 220 ps QQ22 ~ 7 b ~ 7 b

Equivalent to gsbEquivalent to gsb

not a tetrahedral not a tetrahedral band following band following earliest criteriaearliest criteria


What Is The Usual Criteria ?What Is The Usual Criteria ?

• Fingerprints of the symmetry in molecular physics: Fingerprints of the symmetry in molecular physics: branching ratiosbranching ratios

• In nuclear physics? In nuclear physics? That’s theThat’s the ultimate goal but still means a lot of work for ultimate goal but still means a lot of work for theory theory

Have a look at the Have a look at the complexity of complexity of analyzing the analyzing the branching ratios !branching ratios !


Other Point of ViewOther Point of ViewSelf consistent mean field approachSelf consistent mean field approach

iThemba 160Yb exp.iThemba 160Yb exp.


So: What About Experiments So: What About Experiments Now?Now?

• Create a Create a corpus of specific datacorpus of specific data with with current best-instruments:current best-instruments:– Rare-Earth: Rare-Earth: 156156Dy Gammasphere (ANL),Dy Gammasphere (ANL),

156156Gd GAMS (ILL)Gd GAMS (ILL)– Actinides: Orgam (IPNO), Jurogam2 (JYFL)Actinides: Orgam (IPNO), Jurogam2 (JYFL)

• Develop specific instrument whenever Develop specific instrument whenever requested: requested: ELMA projectELMA project T T1/2 1/2

in Actinidesin Actinides


The Actinides: The Actinides: A More Promising Region?A More Promising Region?

““magic numbers” magic numbers” N,Z=90-94,136-142N,Z=90-94,136-142 Elements of interest:Elements of interest:

thoriumthorium uraniumuranium

plutoniumplutonium

Tetrahedral minimum:Tetrahedral minimum:

• 500 keV above GS500 keV above GS• significant barrier: 2.5 significant barrier: 2.5

MeVMeV• maximum effect of maximum effect of octahedral symmetryoctahedral symmetry

Stronger stability Stronger stability than than

prolate/oblate/prolate/oblate/spherical shape spherical shape

coexistencecoexistence


Previous Actinides Studies ofPrevious Actinides Studies of Reflection-Asymmetric ShapesReflection-Asymmetric Shapes

• Theoretical studies of Theoretical studies of (some)(some) octupole bands: octupole bands:– Cranked RPA Cranked RPA Hackman et al. 1998 Hackman et al. 1998 240240Pu & Pu & 248248CmCm– Collective model Collective model Minkov et al. 2006 staggering Minkov et al. 2006 staggering 224,226224,226Ra Ra &&

224,226224,226ThTh– spdfspdf IBA IBA Zamfir et al. 2003-05 U,Pu Zamfir et al. 2003-05 U,Pu && light actin. Z~88 light actin. Z~88– VMI model VMI model Lenis Lenis && Bonatsos 2006 Bonatsos 2006 226226Ra Ra && 226226ThTh– Alpha-particle model Alpha-particle model Shneidman et al. 2002 staggeringShneidman et al. 2002 staggering– Pb core + exotic cluster model Pb core + exotic cluster model Buck et al. 2008 K>0 bandsBuck et al. 2008 K>0 bands

• Experimental evidence:Experimental evidence:– Butler, Cocks et al. 1999-2000 Butler, Cocks et al. 1999-2000 only even-even Rn, Ra only even-even Rn, Ra & & ThTh

– But nothing is said on But nothing is said on U & Pu isotopesU & Pu isotopes


Octupole Degree of Freedom: Octupole Degree of Freedom: a systematic from the levels energya systematic from the levels energy

• Difference in aligned angular Difference in aligned angular momentum momentum (from VMI)(from VMI)

iixx= i= ixx--- i- ixx+ + at a givenat a given • Two limits:Two limits:

– Permanent octupole deformation: Permanent octupole deformation:

i = Ri = R iixx= 0h= 0h– Octupole vibration: Octupole vibration: when the octupole when the octupole

phonon is alignedphonon is aligned

iixx= 3h= 3hK=0-


P. Butler Phys. Scripta T88, 7, 2000P. Butler Phys. Scripta T88, 7, 2000

N ~ 134N ~ 134

Z = 86Z = 86

Z = 88Z = 88

Z = 90Z = 90

““vibrators”vibrators”

““permanent”permanent”

What about U & Pu?What about U & Pu?

00

33


Uranium Isotopes:Uranium Isotopes: very specialvery special

208Pb(22Ne,4n))P. GreenleesP. Greenlees

231Pa(p,4n)) 231Pa(p,2n)) 230Th(,2n)) 232Th(,2n)) 236U(d,pn)) multi-CoulexD. WardD. Ward

No E2’s B(E2)/B(E1)*106

0.4

0.4

0.4

1.3

Hindrance E1’s 3*10-8

P. Zeyen et al. P. Zeyen et al. Z.Phys.A 2328,399 (1987):Z.Phys.A 2328,399 (1987): e- e- coincidence coincidence


Differential alignment: UraniumDifferential alignment: Uranium


Differential alignment: Differential alignment: PlutoniumPlutonium


Comparisons With Mean Fields Comparisons With Mean Fields Predictions Predictions 1 1 ::

Uranium isotopesUranium isotopes

32

20

226

228

230 236

234

232


Comparisons With Mean Fields Comparisons With Mean Fields Predictions Predictions 2 2 ::

Plutonium isotopesPlutonium isotopes

32

20240

242

244


Comparisons With Mean Fields Comparisons With Mean Fields Predictions Predictions 3 3 : :

32

Thorium isotopesThorium isotopes

20

224

226

228 234

232

230


Octupole: Permanent Def. versus Octupole: Permanent Def. versus Vib. Vib.

Thorium isotopesThorium isotopes

30

20

222 224

228226

230 232


Synthesis of The ComparisonSynthesis of The ComparisonA Possible Tetra-IslandA Possible Tetra-Island ? ?

Z/NZ/N 132132 134134 136136 138138 140140 142142 144144 146146

PuPu 228228 240240 242242 244244

UU 226226 228228 230230 232232 234234 236236 238238

ThTh 222222 224224 226226 228228 230230 232232 234234

RaRa 220220 222222 224224 226226 228228

RnRn 220220 222222

OctupoleOctupolepermanentpermanentdeformationdeformation

TetrahedralTetrahedraldeformationdeformation

OctupoleOctupolevibrationvibration


Uranium Isotopes:Uranium Isotopes:

an hypothesis on old measurementsan hypothesis on old measurements

19981998JurosphereJurosphere

P. GreenleesP. Greenlees

1996

8 D. WardD. Ward

1987 P. Zeyen e and 3 1987 P. Zeyen e and 3 detectors detectors

Octupole deformation Octupole deformation Tetrahedral shape Tetrahedral shape Octupole Octupole vibration ?vibration ?

More data requested !More data requested !


What Can Be Done What Can Be Done Experimentally Nowadays?Experimentally Nowadays?

• Revisit the decay schemes to improve the branching ratio measurements: -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)


How to Measure LifetimesHow to Measure Lifetimes in in Light U?Light U?

• With gamma? impossible Plunger : no recoil velocity with the a, p reactionsFast timing: gating not possible above the states of

interest

• With conversion electrons? May Be! (and most probably the only possibility)

The Microwave Method 3-50 ps3-50 ps


Goldring’s Microwave SetupGoldring’s Microwave SetupHF Beam chopper

and beam sweepingcavity

DC

Electromagnetic shutter-like device: selection of electrons

according to their time of emission

, 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

11 22

33very short bursts


Summary & ConclusionsSummary & Conclusions

• Since the launch of the TetraNuc collaborations, Since the launch of the TetraNuc collaborations, 11 experiments11 experiments have been accepted worldwidehave been accepted worldwide

• The first important results have appeared this year in the Rare-Earth The first important results have appeared this year in the Rare-Earth regions bringing regions bringing some proof in contradiction with the simple some proof in contradiction with the simple historical criteriahistorical criteria of the vanishing quadrupole moment for of the vanishing quadrupole moment for 156156GdGd

• More crucial experimental results are expected soon with a plunger More crucial experimental results are expected soon with a plunger experiment at experiment at Gammasphere in Gammasphere in 156156Dy Dy and new results fromand new results from Coulex on Coulex on 156156Gd Gd (LNL-India-Warsaw-Strasbourg)(LNL-India-Warsaw-Strasbourg)

• Meanwhile, important progresses have been made in the more Meanwhile, important progresses have been made in the more promising region of the Actinides that shows the existence of a promising region of the Actinides that shows the existence of a possible island of tetrahedral nucleipossible island of tetrahedral nuclei..

• This possibility is calling for the This possibility is calling for the creation of a modern dedicated creation of a modern dedicated corpus of datacorpus of data

• A possible way to realize this corpus has been formulated through A possible way to realize this corpus has been formulated through the the ELMA ELMA projectproject


List of main List of main TetraNucTetraNuc collaboratorscollaborators

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, LyonF. Azaiez, F. Ibrahim, C.Petrache, D. Verney IPN, Orsay A. Astier, I. Deloncle, A. Korichi CSNSM, OrsayD.J. Hartley US Naval Academy, AnnapolisN.Dubray CEA, Bruyères-le-ChâtelJ F. Sharpey-Schafer iTHemba, Cape-TownCh. Schmitt Ganil, CaenJ. Gerl GSI, DarmstadtB. Lauss, J. Jentschel, W. Urban ILL,GrenobleP.T. Greenlees, P. Jones, R. Julin, et al. JYFL, JyvaskylaP. Bednarczyk, B. Fornal, A. Maj, K. Mazurek, K. Zuber IFJ-PAN, KrakowT. Bhattacharjee, S. K. Basu et al. VECC, KolkataG. de Angelis et al. INFN, LegnaroA. Gozdz, A. Dobrowolski - University of LublinR.P. Singh, S. Muralithar, R. Kumar, et al. IUAC, New Delhi D. Tonev BAS, SofiaL. Riedinger (and the US Gammasphere collaboration), N. Schunck University of

TennesseeJ. Srebrny, M. Zielinska SLCJ, Warsaw J. Dobaczewski, P. Olbratowski Warsaw University

Thank Thank you!!

TetraNuc Collaboration

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