Li, Be, B induced reactions to study the yrast and non-yrast states in nuclei with A ~ 130 R. Palit Department of Nuclear and Atomic Physics Tata Institute of Fundamental Research Mumbai Outline of Talk: Motivation Experimental Results Comparison with model calculations Possibilities with INGA

Features near A ~ 130 Nuclei in this region have valance protons in low  orbitals and neutrons in high  orbitals Nd Ce Ba Cs Xe I Z 50 N N=82

Interesting Structure Phenomena near A ~ 130 Different shapes & excitation modes Critical point symmetry Magnetic rotation, Degenerate dipole bands, Highly deformed bands Gamma vibration, Octupole correlation Both yrast and non-yrast spectroscopic studies are needed to probe these features 132Xe: One of the better examples of E(5) symmetry? Quasi-particle structures: Shape co-existence effect in 135Ba dipole bands New degenerate dipole bands & gamma bands in 131Cs

Experiment hall LINAC

Experimental setup Clover array with 14 NaI(Tl) multiplicity filter 11B + 124Sn @ 46 MeV Au backed target 150 million events in background subtracted  matrix

Excitation Function for 9Be + 130Te 6

Critical point symmetry F. Iachello (2000) proposed - Critical point symmetries in shape transition of nucleus. They are E(5) and X(5) symmetries Casten et al (2000) : Best example for E(5) symmetry : 134Ba.

Key experimental signatures for E(5) symmetry: Clark et al. (2004) The energy ratio E(41+) /E(21+) should be approximately 2.20. The B(E2; 41+  21+) value should be approximately 1.5 times the B(E2; 21+  01+) value. There should be two excited 0+ states lying at approximately 3–4 times the energy of the 21+ state. The decay of the 0ξ+ state should also be characteristic of E(5). There is an allowed transition to the 21+ level with strength of approximately 0.5 the B(E2; 21+  01+) value. Fig. Variation of R4/2 with the proton number for N = 78 isotones [ENSDF data].

Motivation and experimental Details The previously known best example for E(5) symmetry 134Ba has been shown to satisfy most of the empirical signatures. The 134Ba nucleus has R4/2 value (2.31), which is slightly more than the ideal value for E(5) symmetry. This suggests that this nucleus lies to the right side [SO(6) side] of critical point. In the case of 132Xe, the R4/2 value (2.16) lies very close to the ideal value for the E(5) symmetry indicating that it lies more towards the U(5) side 9 9

Fig. Partial Level Scheme

Fig. The positions of energy levels for Ba isotopes. [ ENSDF data]

Fig. The positions of energy levels for Xe isotopes. [ ENSDF data]

Fig. The variation of the ratio of the two excited 0+ levels for Te, Xe and Ba with the neutron number. The theoretical value of this ratio predicted for E(5) symmetry is 1.18. [ENSDF data]

132Xe E(5) Theoretical Fig. Comparison of Normalized partial level scheme which is theoretically predicted by Iachello (2000) with that obtained for 132Xe. The * mark represents the transitions obtained in the present work for the first time.

Possible evidence of E(5) symmetry in 132Xe The evidence for state of the ξ = 2 band was obtained for the first time in the experiment for the E(5) Nuclei. The level scheme shown has two excited 0+ levels which are denoted 0τ+and 0ξ+. The 0τ+ state has been deduced from the reaction data [Alford (1979)]. The strong transition of gamma ray with energy 1193.0 keV from the 0+ level to the 21+ suggests that the 0+ level is the 0ξ+ level .

Summary of 132Xe Possible evidence of E(5) symmetry in 132Xe. The evidences for the ξ = 2 band was obtained for the first time in the experiment. Positioning of two 0+ levels plays vital role in describing the critical point symmetry. Further experiments are needed to find the transition probabilities and hence to confirm the E(5) symmetry. Ref: (3He,n) reaction W.P Alford, et. al., NPA323 (1979) 339.

Quasi-particle bands at intermediate spin in 135Ba With spin large change in nuclear shape was observed, e.g., 139,140Nd Little was known on low and intermediate spins for 139Nd and 135Ba Magnetic rotational bands have been identified in neighboring isotopes of Ce, Nd, Sm S. J. Zhu et al. (2000)

Previously Known Level Scheme of 135Ba E. Dragulescu et al., Rev. Roum. Phys. 32, 743 (1987) Shapes co-existences in 135Ba 18

Gated Spectra 19 High spin states and shapes co-existences in 135Ba

New Level Scheme 20

Comparison of Band 2 with Tilted Axis Cranking Model

Existence of Multiple minima in gamma deformation We have established a shape coexistence of near prolate, triaxial, and oblate shapes, which results from the existence of multiple  deformation with  ~ 0.09. 22 High spin states and shapes co-existences in 135Ba (to be submitted in PRC).

Ref: S. Kumar, R. Palit, et. al. PRC (2007), Ph.D. Thesis of S. Kumar The Possible configurations suggested for some states in 139Nd and 135Ba compared to those in N=79 odd Nuclei. Ref: S. Kumar, R. Palit, et. al. PRC (2007), Ph.D. Thesis of S. Kumar

Multiple band structure of 131Cs Chiral twin bands have been identified in odd-odd Cs isotopes based on Ref: T. Kokie PRC67, 044319 (2003) What happens to a similar configuration in 131Cs? Alternative explanation for degenerate dipole bands Triaxial even-even core: Gamma bands built on different quasi-particle configurations 130Cs

Summary of the present experimental results The high spin structure of 131Cs has been extensively investigated through in-beam gamma spectroscopy with the Clover array at BARC-TIFR accelerator facility. High spin states upto 7 MeV excitation energy & 49/2 ћ ~400 transitions, ~ 150 excited states arranged in 15 bands These show a variety of collective structure. degenerated dipole bands, gamma vibrational bands built on one quasi-particle bands Previous work: U. Garg et. Al, PRC19 207 (1979), R. Kumar, et. Al., EPJ24, 13 (2005)

S. Sihotra, R.Palit, Z. Naik, et. al. Partial level scheme produced in our experiment S. Sihotra, R.Palit, Z. Naik, et. al.

Theoretically it is a challenge to give microscopic explanation to all the collective excitation observed in this nuclei. We have used deformed Hartree-Fock and Angular Momentum Projection technique for this purpose. This is a microscopic model which give quantum mechanical description to collective rotation and its coupling with single particle excitations.

Electromagnetic matrix Hartree-Fock Calculation Deformed Single Particle HF Orbits Prolate or Oblate Intrinsic Configuration Band Structures and Electromagnetic matrix elements Band-Mixing Angular Momentum Projection Z. Naik, C.R. Praharaj, PRC67 054318 (2003)

Neutron (Energy in MeV) Active Protons and Neutrons Core 90Zr Spherical inert core Residual Interaction Surface -  Interaction Interaction strengths 0.336 MeV Proton (Energy in MeV) 1g9/2 2d5/2 1g7/2 1h11/2 2d3/2 3s1/2 1h9/2 -6.541 0. 0.64 0.8 3.288 3.654 5.033 Model Spaces Neutron (Energy in MeV) 2d5/2 1g7/2 3s1/2 2d3/2 1h11/2 1f7/2 1h9/2 -6.4 -6.0 -4.848 -4.577 -3.2 1.592 2.106

||π are denoted in the figure. Each orbit is doubly degenerated.

2J are indicated in the figure Configurations Band-4 :- (g9/2)- 1 Band-5 :- (g7/2)1 Band-6 :- (d5/2)1

Two protons alignment band of bands 5 and 6 Band 7:- K=5/2+ π(g7/2)1(h11/2)2 Band 8:- K=3/2+ π(d5/2)1(h11/2)2 Also we have mixed K=5/2+ π(d5/2)1(h11/2)2(h11/2)2 with band 8 Favoured Unfavoured Unfavoured Favoured 2J are indicated in the figure

Positive parity doublet bands Spectra of these two bands B2 & B3 are reproduced with configurations (h11/2)1(h11/2)1(d3/2/s1/2)1 but not with previously suggested configurations ((d5/2/g7/2)1 (h11/2)2). This is also confirmed with TAC calculation and systematic of nuclei.

Comparison of B(M1)/B(E2) values for B2 and B3 We have consider effective charges 1.7 e and 0.7 e for proton and neutron respectively.

Continuation of ….. TAC , Systametics for B2 & B3 Comparison with TAC result Systametics of nuclei K. Singh, et. Al., EPJ A27 321 (2006)

Newly observed three-quasi-particle negative parity bands. Band 12 : - K=11/2- π1/2-(h11/2) 7/2+(g7/2) 3/2+(d3/2) Band 13 : - K=9/2- π1/2-(h11/2) 7/2+(g7/2) 1/2+(s1/2) Band 14 : - K=11/2- π9/2+(g9/2) 1/2+(d5/2) 1/2-(h11/2) We have considered Band 14 as three quasi- proton bands

Comparison of B(M1)/B(E2) values for B12, B13 and B14 We have consider effective charges 1.7 e and 0.7 e for proton and neutron respectively.

Reported gamma bands in 125Cs and 127Cs Only with h11/2 K. Singh, et. Al., EPJ A27 321 (2006) Y. Liang, et. Al. PRC 42 890(1990)

Comparison of gamma vibrational bands of 131Cs with 130Xe Staggering in g7/2 is similar to 130Xe B1 (Gamma band built on pg7/2) band head 11/2+ is not identified. B9 (Gamma band built on ph11/2) Bands are accordingly normalized for comparison g7/2 h11/2 Ref: S. Sihotra, et. al., submitted

further supported by TAC results and systematics Summary for 131Cs: Spectroscopic data of the different 1-qp bands & 3-qp rotational aligned bands have been explained. A pair of closely placedI = 1 bands have been reassigned 3 qp-configurations based on PHF calculation. further supported by TAC results and systematics Configurations have been assigned to newly observed three quasi-particle bands. The PHF calculations based on surface delta interactions seem to be quite successful in explaining many features of large spectroscopic data on high spin states available from large detector array like INGA Gives a microscopic picture of the different dynamics involved in generation of angular momentum in atomic nuclei

Large Array of Detectors within India for Nuclear Structure Study 2d-plot for ZC & ballastic method Indian National Gamma Array @IUAC Charged Particle Detector @TIFR Collaboration: Universities, TIFR, IUAC, SINP, IUC, SINP, BARC, VECC Array will move between Mumbai-Delhi-Kolkata

Conclusion Recent results from spectroscopy of A ~ 130 region have been discussed. Both yrast and non-yrast states were explored with Li, Be & B induced reactions. With the Indian National Gamma Array (24 Clover detectors) coupled with other ancillary devices, the spectroscopy of various nuclei with stable ion beams from Pelletron machine and LINAC will be pursued. Recent experiments Lifetime measurements in A ~ 110, 130 (magnetic & degenerate dipole bands) (TIFR & others) Neutron rich isotopes with 16,18O + 18O reactions (IUC & others)

Full INGA Collaboration S. Kumar2,3, S. Sihotra4, Z. Naik1, A. Raghav1, A.Y. Deo1, P.K. Joshi1, I. Mazumdar1, A.K. Jain2, H.C. Jain1 1Tata Institute of Fundamental Research, Mumbai, India 2Department of Physics, IIT, Roorkee, India 3University of Delhi, New Delhi, India 4Department of Physics, Guru Nanak Dev University, Amritsar, India Acknowledgement: Full INGA Collaboration

Thank You

2J are indicated in the figure Band-10 :- (h11/2)1 Band-11 :- (h11/2)1(h11/2)2 For both bands 10 and 11 we have mixed two more align bands which are obtained by exciting proton from 1/2- to 3/2- and 5/2- orbits respectively. Signature effect observed in these bands are reproduced with calculation.