Transcript Document

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
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
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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
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Experiment hall
LINAC
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Experimental setup
Clover array with 14 NaI(Tl) multiplicity filter
11B
+ 124Sn @ 46 MeV
Au 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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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
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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.
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[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
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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 .
R4/2
E(0+2,0)
E(0+3,1)
E(0+3,1)
B(E2; 4+1,2  2+1,1 )
E(2+1,1)
E(2+1,1)
E(0+2,0)
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)
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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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Previously Known Level Scheme of 135Ba
E. Dragulescu et al.,
Rev. Roum. Phys. 32, 743 (1987)
Shapes co-existences in 135Ba
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Gated Spectra
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).
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The Possible configurations suggested for some states in
139Nd and 135Ba compared to those in N=79 odd Nuclei.
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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
h11/ 2 h11/ 2
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
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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.
Previous work: U. Garg et. Al, PRC19 207 (1979),
R. Kumar, et. Al., EPJ24, 13 (2005)
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
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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
Band Structures
and
Electromagnetic matrix
elements
Band-Mixing
Intrinsic
Configuration
Angular Momentum
Projection
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Z. Naik, C.R. Praharaj, PRC67 054318 (2003)
Active Protons and
Neutrons
90Zr
Core
Spherical inert
core
Surface -  Interaction
Residual
Interaction


V
(
r
)


V

(

)

(

)

12
0
lm
lm
lm
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
1h9/2
Model
Spaces
Neutron (Energy in MeV)
2d5/2
1g7/2
3s1/2
2d3/2
1h11/2
1f7/2
-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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2J are indicated in the figure
Configurations
Band-4
:(g
)
9/2
1
Band-5 :- (g7/2)1
Band-6 :- (d5/2)1
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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
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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.
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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=11/2π1/2-(h11/2) 7/2+(g7/2)
3/2+(d3/2)
Band 13 : - K=9/2π1/2-(h11/2) 7/2+(g7/2)
1/2+(s1/2)
Band 14 : - K=11/2π9/2+(g9/2) 1/2+(d5/2) 1/2-(h11/2)
We
have
considered
Band 14 as three quasiproton 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
Only with h11/2
K. Singh, et. Al., EPJ A27 321 (2006)
Y. Liang, et. Al. PRC 42 890(1990)
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Comparison of gamma vibrational bands of 131Cs with 130Xe
Staggering in g7/2
is similar to 130Xe
g7/2
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 comparison
h11/2
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Ref: S. Sihotra, et. al., submitted
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
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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
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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, 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
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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
3/2and
5/2orbits
respectively.
Signature effect observed in
these bands are reproduced
with calculation.
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