New insights into the nuclear structure in n-rich Pd Ru isotopes

Y.X. Luo 1,2

1 Vanderbilt University, 2 LBNL at BerkeleyTalk at IWNDT, Texas A&M University, College Station, Texas, August 19-22, 2013

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

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 A=108 to A=110 and 112 J. Aysto et al., Nucl. Phys. A515, 365(1990)

M. Caprio, Phys. Rev. C83, 064309(2011) 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 symmetricMaximum triaxial

Global search for triaxiality, Mller 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.

Previous understanding of Pd and Ru isotopesAnharmonic 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

Previous experimental studies Coulomb excitations, transfer reactions, - decay, fission etc., J. yst et al., Phys. Lett. B201, 211(1988); Nucl. Phys. A480, 104(1988); H. Penttil et al., Phys. Rev. C44, 935(1991)30. A. Jokinen et al., Eur. Phys. J. A9, 9(2000), and the references thereinPreliminary 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. Krcken 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. Krcken 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)

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

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.

A triple-gated 4d spectrum showing the identifications of doublet bands

Angular correlation for odd-parity band, band 4 of 114Pd

Angular correlations

I. Observations and studies of chiral symmetry breaking inRu and Pd

The prototype of a triaxial chiral rotorS. Frauendorf and J. Meng, Nucl. Phys. A617, 131(1997)

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

Fingerprints of Chiral doublets I=1 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

Level scheme of 112Rudouble g bandgbg band

I=1 odd-parity bands.

First observation of I = 1 doublet bands in 112Ru

First observation of I = 1 doublet bands in 110Ru

Energy degeneracy: Energy differences of partner levels

Signature splitting of the odd-parity band 4 & 5 in 110,112Ru and 112,114,116Pd[E(I) - E(I-1)] [I(I+1) - (I-2)(I-1)][E(I) - E(I-2)][I(I+1) - (I-1)I]S(I) = 1

Signature splitting of the odd-parity band 6 & 7 in 110,112Ru and 112,114,116Pd[E(I) - E(I-1)] [I(I+1) - (I-2)(I-1)][E(I) - E(I-2)][I(I+1) - (I-1)I]S(I) = 1

Signature splitting of the odd-parity band 4 & 5 in 110,112Ru and 106,108Mo[E(I) - E(I-1)] [I(I+1) - (I-2)(I-1)][E(I) - E(I-2)][I(I+1) - (I-1)I]S(I) = 1

Best fit for 110,112Ru by rigid triaxial rotor model IBM1+V3 Ex, B(E2), signature splitting

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))

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).

Evolutions of chiral structure

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. degrd, et al., Phys. Rev. Lett. 86, 5866(2001); G. Schnwaer 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)

Fingerprint of the wobbling excitation (WE) Two phonon WE (even-spin) is above the one Phonon WE (odd-spin) (M. Caprio, 83, 014303(2010)).

First e-e-wobblerodd I low

N=64 No WE

N=66 No WE until spin 6 and 10 in 110Ru and 112Pd, respectivelyN=66

N=68 Onset of WE at low and moderate spins in 112Ru and 114Pd 114Pd e-e wobblerNwobbling = 2 Nwobbling = 1N=68

N=70 WE may also be seen with small separations in 114Ru and 116Pd

Final RemarksEvolutions from chiral symmetry breaking with maximum triaxiality in Ru to disturbed chiral structure with less pronounced triaxiality in Pd were identified from Z=44 (Ru) to Z=46 (Pd), for N=66 and N=68 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 N=64 to onset of WE at N=68, with N=66 being transitional with regard to WE.

Maximum triaxiality is reached at N=68 for both Ru and Pd, 4 more neutrons than the predictions by the theories.

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

Thank you very much for your attention!