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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

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Features near A ~ 130

N

Z

N=82

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Nuclei in this region have valance protons

in low orbitals and neutrons in high orbitals

CsBa

XeI

Ce

Nd

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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

Interesting Structure Phenomena near A ~ 130

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

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Experiment hall LINAC

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Experimental setup Clover array with 14 NaI(Tl) multiplicity filter

11B + 124Sn @ 46 MeVAu backed target

150 million events in background subtracted

matrix

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Excitation Function for 9Be + 130Te

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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.

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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].

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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

Motivation and experimental

Details

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Fig. Partial Level Scheme

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

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

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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]

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132XeE(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.

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R4/2 E(0+2,0) E(2+1,1) E(0+3,1) E(2+1,1)

E(0+3,1)E(0+2,0) B(E2; 4+1,2 2+1,1 ) B(E2; 2+1,2 0+1,0 )E(5) 2.20 3.03 3.59 1.18 1.68

132Xe 2.16 2.79 3.73 1.33 1.24(13)134Ba 2.31 3.57 2.91 0.815 1.56(18)

R4/2 E(0+2,0) E(2+1,1) E(0+3,1) E(2+1,1)

E(0+3,1)E(0+2,0) B(E2; 4+1,2 2+1,1 ) B(E2; 2+1,2 0+1,0 )E(5) 2.20 3.03 3.59 1.18 1.68

132Xe 2.16 2.79 3.73 1.33 1.24(13)134Ba 2.31 3.57 2.91 0.815 1.56(18)

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 .

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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.

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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)

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E. Dragulescu et al., Rev. Roum. Phys. 32, 743 (1987)

Previously Known Level Scheme of 135Ba

Shapes co-existences in 135Ba Shapes co-existences in 135Ba

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Gated Spectra

High spin states and shapes co-existences in 135Ba High spin states and shapes co-existences in 135Ba

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New Level Scheme

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Comparison of Band 2 with Tilted Axis Cranking Model

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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.

High spin states and shapes co-existences in 135Ba (to be submitted in PRC).High spin states and shapes co-existences in 135Ba (to be submitted in PRC).

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Ref: S. Kumar, R. Palit, et. al.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.

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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

2/112/11 hh

130Cs

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• 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

Summary of the present experimental results

Previous work: U. Garg et. Al, PRC19 207 (1979), R. Kumar, et. Al., EPJ24, 13 (2005)

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Partial level scheme produced in our experiment

S. Sihotra, R.Palit, Z. Naik, et. al.

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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.

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Hartree-Fock Calculation

Deformed Single Particle HF Orbits

Prolate or Oblate

Intrinsic

Configuration

Angular MomentumProjection

Band-Mixing

Band Structures and

Electromagnetic matrix elements

Z. Naik, C.R. Praharaj, PRC67 054318 (2003)

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Core

ResidualInteraction

Model Spaces

90Zr

Active Protons and Neutrons

Spherical inert core

Surface - Interaction

Interaction strengths 0.336 MeV

)()()( 012 lm

lmlmVrV

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

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

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||π are denoted in the figure.

Each orbit is doubly degenerated.

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Configurations

Band-4 :- (g9/2)-1

Band-5 :- (g7/2)1

Band-6 :- (d5/2)1

2J are indicated in the figure

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2J are indicated in the figure

Favoured FavouredUnfavoured Unfavoured

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

Band 7:- K=5/2+

π(g7/2)1(h11/2)2

Two protons alignment band of bands 5 and 6

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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.

Positive parity doublet bands

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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.

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Continuation of ….. TAC , Systametics for B2 & B3

Comparison with TAC result Systametics of nuclei

K. Singh, et. Al., EPJ A27 321 (2006)

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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

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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.

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Reported gamma bands in 125Cs and 127Cs

K. Singh, et. Al., EPJ A27 321 (2006) Y. Liang, et. Al. PRC 42 890(1990)

Only with h11/2

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Comparison of gamma vibrational bands of 131Cs with 130Xe

B1 (Gamma band built on g7/2) band head 11/2+ is not identified. B9 (Gamma band built on h11/2)

Bands are accordingly normalized for comparisong7/2 h11/2

Staggering in g7/2

is similar to 130Xe

Ref: S. Sihotra, et. al., submitted

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Summary for 131Cs:

Spectroscopic data of the different 1-qp bands & 3-qp rotational aligned bands have been explained.

A pair of closely placedI = 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

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Large Array of Detectors within Indiafor

Nuclear Structure Study

Indian National Gamma Array@IUAC

Charged Particle Detector@TIFR

Collaboration: Universities, TIFR, IUAC, SINP, IUC, SINP, BARC, VECC

2d-plot for ZC & ballastic method

Array will move between Mumbai-Delhi-Kolkata

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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)

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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, India2Department of Physics, IIT, Roorkee, India

3University of Delhi, New Delhi, India4Department of Physics, Guru Nanak Dev University, Amritsar, India

Acknowledgement:Full INGA Collaboration

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Band-10 :- (h11/2)1

Band-11 :- (h11/2)1(h11/2)2

Signature effect observed in these bands are reproduced with calculation.

2J are indicated in the figure

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.

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49

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