New insights into the nuclear structure in n-rich Pd

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New insights into the nuclear structure in
n-rich Pd Ru isotopesY.X. Luo 1,21
Vanderbilt University, 2 LBNL at Berkeley

• Talk at IWNDT, Texas AM University, College
  Station, Texas, August 19-22, 2013

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Search and study of new excitations
Chiral symmetry breaking Wobbling
excitation
Triaxial
Triaxial

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Our systematic search and studies were motivated
by the following

• Hartree-Fock calculations for Ru
• ? shape transition from prolate towards
  triaxial as one goes from A108 to A110 and 112
• J. Aysto et al., Nucl. Phys. A515,
• 365(1990)

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Y.X. Luo et al., Phys. Rev. C74, 024308(2006)
Y.X. Luo et al., J. Phys. G31, 1303(2005)
Y.X. Luo et al., Phys. Rev. C70, 044310(2004)
Y.X. Luo et al., Phys. Rev. C69, 024315(2004)
one quasi-particle plus triaxial rotor
calculations
Axially symmetric
Maximum triaxial
M. Caprio, Phys. Rev. C83, 064309(2011)
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Global search for triaxiality, Möller et al.
predicted Largest lowering of Egs centered
around 108Ru and 110Pd, with energy gain with
regard to axial shape being 0.67 and 0.32 MeV,
respectively.
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Previous understanding of Pd and Ru isotopes

• Anharmonic vibration ? soft rotor Mixed symmetry
  states identified IBM/IBM2 study of even-even Pd
  isotopes
• ( J. Stachel, et al., Phys. Rev. C25,
  650(1982), Ka-Hae Kim et al., Nucl. Phys. A604,
  163(1996)
• Band-crossings and predictions of shape
  transitions from prolate to oblate P.H. Regan et
  al., Phys. Rev. C55, 2305 (1997) G.A. Lalazissis
  et al, At. Data Nucl. Data Tables. 71, 1(1999)
  ---- not proved !
• Rigid rotors, band-crossings, ? band and double ?
  band in Ru isotopes

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Previous experimental studies

• Coulomb excitations, transfer reactions, ß-
  decay, fission etc., J. Äystö et al., Phys. Lett.
  B201, 211(1988) Nucl. Phys. A480, 104(1988)
  H. Penttilä et al., Phys. Rev. C44, 935(1991)30.
  A. Jokinen et al., Eur. Phys. J. A9, 9(2000),
  and the references therein
• Preliminary studies of prompt fission gs
  
• R. Aryaeinejad et al. Phys. Rev. C48,
  566(1993) J. Hamilton et al., Prog. Part. Nucl.
  Phys. 35, 635(1995) M. Houry et al., Eur. Phys.
  J. A6, 43(1999) K. Butler-Moore et al., J Phys.
  G. Nucl. Part. Phys. 25, 2253(1999) T. Kutsarova
  et al., Phys. Rev. C58, 1966(1998) R. Krücken
  et al., Phys. Rev. C60,031302(1999) X. Q. Zhang
  et al., Phys. Rev. C61, 014305(2000) W. Urban et
  al., Eur. Phys. J. A22, 157(2004) R. Krücken et
  al., Eur. Phys. J. A10, 151(2001) S. Lalkovski
  et al., Eur. Phys. J. A18, 589(2003) X. Q. Zhang
  et al., Phys. Rev. C63, 027302(2001) D. Fong et
  al., Phys. Rev. C72, 014315(2005) M. A. Stoyer
  et al., Nucl. Phys. A787, 455c(2007)

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Very weak population - the most serious challenge

• prompt ? rays from 252Cf fission ?
• A gold mine for production and studies
• Accumulation of as high as 5.7 1011 events
• plus ?-?-?-?, ?-? (?) measurements
• 4d Hypercube data

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Identifications of the transitions of Ru and Pd
isotopes are achieved by cross-checking
coincidence relationship of ?s between partners
Ru-Xe and Pd-Te, respectively.
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A triple-gated 4d spectrum showing the
identifications of doublet bands
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Angular correlation for odd-parity band, band 4
of 114Pd
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Angular correlations
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I. Observations and studies of chiral
symmetry breaking inRu and Pd
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The prototype of a triaxial chiral rotor
S. Frauendorf and J. Meng, Nucl. Phys. A617,
131(1997)
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Chirality, or handeness, in nucleus is the study
of right- or left- handed symmetry in nucleus
RZ the rotation about the z axis, T Time
reversal
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Fingerprints of Chiral doublets

• ?I1 doublet bands nearly degenerate in energy
  for the partner levels (Ip)
• Partner level in each doublet having similar
  electromagnetic properties such as similar
  B(E2)/B(M1) ratios similar structure
• Nearly constant signature splitting with spins
  and equal value for partner level

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Level scheme of 112Ru
.
double g band
gb
g band
?I1 odd-parity bands
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First observation of ?I 1 doublet bands in
112Ru

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First observation of ?I 1 doublet bands in
110Ru

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Energy degeneracy Energy differences of partner
levels
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Signature splitting of the odd-parity band 4 5
in 110,112Ru and 112,114,116Pd
E(I) - E(I-1) I(I1) - (I-2)(I-1)
S(I)
- 1
E(I) - E(I-2)I(I1) - (I-1)I
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Signature splitting of the odd-parity band 6 7
in 110,112Ru and 112,114,116Pd
E(I) - E(I-1) I(I1) - (I-2)(I-1)
S(I)
- 1
E(I) - E(I-2)I(I1) - (I-1)I
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Signature splitting of the odd-parity band 4 5
in 110,112Ru and 106,108Mo
E(I) - E(I-1) I(I1) - (I-2)(I-1)
S(I)
- 1
E(I) - E(I-2)I(I1) - (I-1)I
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Best fit for 110,112Ru by rigid triaxial rotor
model IBM1V3
Ex, B(E2), signature splitting
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However, ?-softness was implied in 108Ru

• Fit of IBM1 model to Eexc , B(E2) and
  signature splittings of 108Ru implied
• ?
• a ? soft SU(6) nucleus
• ?
• ? softness disturbing the chiral symmetry
  breaking in 108Ru
• also observed in 106Ag (P. Joshi et al. PRL,
• 98,102501(2007))

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Evolutions of chiral structure

• We suggest chiral symmetry breaking in
  110,112Ru with maximum triaxial deformation
• (energy gain as large as 0.67 MeV)
• Disturbed chirality in 108Ru by ?-softness
• Disturbed chiral symmetry breaking in Pd
• by less-pronounced triaxiality
• (energy gain 0.32 MeV).

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II. Onset and evolutions of triaxial
wobbling motions in Ru and Pd Wobbling
Excitation A revolving motion of J about an
axis of the triaxial nucleus seen in
161,163,165,167Lu and 167Ta at high spinS. W.
Ødegård, et al., Phys. Rev. Lett. 86,
5866(2001) G. Schonwaßer et al, Phys. Lett,
B552, 9(2003) P. Bringel et al., Eur. Phys. J.
A24, 167(2005) H. Amro et al., Phys. Lett.
B553, 197(2003) D. J. Hartley et al, Phys. Rev.
C80, 041304(R)(2009) C83, 064307(2011)
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• Fingerprint of the wobbling excitation (WE)
• Two phonon WE (even-spin) is above the
• one Phonon WE (odd-spin)
• (M. Caprio, 83, 014303(2010)).

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First e-e-wobbler
odd I low
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N64 No WE
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N66 No WE until spin 6 and 10 in 110Ru and
112Pd, respectively
N66
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N68 Onset of WE at low and moderate spins
in 112Ru and 114Pd 114Pd e-e wobbler
N68
Nwobbling 2
Nwobbling 1
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N70 WE may also be seen with small separations
in 114Ru and 116Pd
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Final Remarks

• Evolutions from chiral symmetry breaking with
  maximum triaxiality in Ru to disturbed chiral
  structure with less pronounced triaxiality in Pd
  were identified from Z44 (Ru) to Z46 (Pd), for
  N66 and N68 isotonic chain, respectively.
• Wobbling excitations were identified at low and
  moderate spins in 112Ru and 114Pd, may be also in
  116Pd and 114Ru. Evolution from no WE at N64 to
  onset of WE at N68, with N66 being transitional
  with regard to WE.

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• Maximum triaxiality is reached at N68 for both
  Ru and Pd, 4 more neutrons than the predictions
  by the theories.

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Collaborators Y.X. Luo, J.H.
Hamilton, J.O. Rasmussen, A.V. Ramayya, S.
Frauendorf, J.K. Hwang, N.J. Stone, S.J. Zhu,
N.T. Brewer, E. Wang, I.Y. Lee, S.H. Liu, G.M.
TerAkopian, A.V. Danie, Yu. Ts. Oganessian, M.A.
Stoyer, R. Donangelo, W. C. Ma, J.D. Cole, Yue
Shi, and F.R. Xu
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Thank you very much for your attention!