Octupole Correlation in Xe-Cs-Ba nuclei

The nuclei around A∼130 mass region below N = 82 shell closure are γ-soft deformed nuclei at low and intermediate spins, and exhibit various intriguing phenomena. Various possible and associated phenomena have been discussed in order to make it more lucid. Octupole correlation represents the structural behavior of the atomic nuclei at high spin which can arise when nucleons near the Fermi surface occupy states of opposite parity with orbital and total angular momentum differing by 3ħ. A nucleus with octupole deformation has reflection asymmetric shape. It has seen that the maximum octupole coupling occur just above the close shells (Z, N = 34, 56, 88 and 134). Octupole correlation is essential property in order to describe the energy of low lying collective negative parity states and E1/E3 transition strengths. Several theoretical calculations and experimental results have suggested the presence of octupole correlation in Ba, Cs and Xe isotopes. This work highlights the absence of any satisfactory conclusion for octupole correlation and reiterates the need for calculations to be performed for the better results about octupole correlation in this mass region Keywords— γ-γ coincidence, spin-parity, fusion evaporation reaction, Electromagnetic transitions, γ-transitions and level energy.


INTRODUCTION
For nuclear structure theory, octupole deformed nuclei have exceptionally importance can be characterized by the the breaking of reflection symmetry. Octupole correlation in atomic nuclei is due to the interaction between the orbitals of opposite parity whose angular momentum differ by 3 units (∆j = ∆l = 3) near Fermi level. This situation is found between an intruder orbital and normal parity sub-shell i.e. for particle number 34 (g 9/2→ p 3/2 ), 56 (h 11/2 →d 5/2 ), 88 (i 13/2 →f 7/2 ) and 134 (j 15/2 →g 9/2 ). The nuclei that have their Fermi surface in close proximity to these pair of orbitals will be particularly susceptible to octupole correlation effect. Such orbital play an important role in generating spin of heavy rotating nuclei and gives rise to the characteristics backbending phenomenon, observed commonly in nuclei with quadrupole deformation.
Quadrupole-octupole coupling is small for quadrupole deformed nuclei, but a more systematic calculation covering spherical or near spherical is in order. One of the interesting point is the observation that these octupole correlation can develop or be enhanced as a consequence of dynamical effects, which cause an energy shift of effective orbitals, like the deformation induced by rapid rotation of excited nuclei. Octupole correlations are essential to describe the energy of low lying collective negative parity states and E1 and E3 strenghts. They also have an impact on binding energy and quantity like nucleon separation energy. Octupole shape has weaker pairing correlation, which increases the momemt of inertia. Also with increasing rotational frequency, the reflection asymmetric minimum shift towards larger values of β 1 and β 2 and smaller β 3 [1]. Hamilton et al. [2] gives the experimental evidence which supporting this fact.
The purpose of the present investigation is to reinvestigate the octupole correlation in isotopes of Xe, Cs Ba nuclei. We have noted in our study that experimental observation of octupole correlation in 117 Xe is not in agreement with the theoretical calculations and calls for further theoretical studies in this region. The theoretical calculations have also predicted the octupole softness in 138−148 Xe, but till date there is no experimental evidence in this region. This work reports the absence of any satisfactory conclusion for octupole correlation and reiterates the need for calculations to be performed for the better results. Furthermore it was noted that only few lifetime data have been published so far. So it needs further investigation.
The paper is organized as follows, Section I contains the introduction of octupole correlation, Section II contain the related work, Section III describes results and discussion and finally Section IV concludes the present work.
in fact long established in proximiting N=88, Z=56 corresponding to 144 Ba and Z=56, N=56 corresponding to 112 Ba. An obvious manifestation of reflection asymmetry in nuclei is the occurrence of low-lying negative-parity states which are collective in nature. States having such properties were first identified in Ra and Th isotopes with N=136 by the Berkeley group [3] using α-spectroscopy. In this mass region the 1and 3states remain energetically higher than the 2 + and 4 + states, respectively, which rules out a simple interpretation in terms of octupole deformation. In 124 Ba [4], the low lying negative parity states have also been observed. For actinide nuclei, the minimum of the energy of negativeparity states is very localized in N, while there are insufficient data to determine the corresponding localization in Z. For the lanthanide region, this minimum value is attained outside the transitional region where octupole effects are strongest (N≥90). The systematic behavior of excited negative-parity states has been discussed by several authors [5,6]. Peker et al. [6] has concluded that a vibrational interpretation is appropriate and that the behavior of the negative-parity states can be explained in terms of Coriolis coupling between the K π = 0 -, 1 -, 2 -, and 3band heads. Zamfir et al., [7] have established a simple parameterization for the energies of 3states in all nuclei with A≥30 and conclude that deviations from normal behavior characterize nuclei, having the strongest octupole correlations (they are in the transitional lanthanide and actinide regions).
A common property of nuclei exhibiting the features of octupole correlation is the occurrence of relatively enhanced E1 and E3 transitions between the yrast positive and negative parity bands. The first observations of such band structure in heavy nuclei were in 218 Ra [8] and 222 Th [9]. In mediummass nuclei, sequences of nuclear states with similar features were observed much earlier, the first connection with static octupole deformation in this mass region was made by Phillips et al. [10], who studied 142,144,146 Ba using fission spectroscopy.

III. RESULTS AND DISCUSSION
In this Section we will discuss results of the isotopes of Ba, Cs and Xe one by one.

A. Octupole correlation in 118,120,122,124,125 Ba
Smith et al. have reported the first observation of excited states in 118 Ba which is the most neutron-deficient barium isotope to which excited states are assigned [11]. The ground-state band and a side band are observed upto spins 20ħ and 17ħ, respectively. The side band decays into the ground-state via three transitions which presumably have E1 character. This structure is suggestive of octupole correlation. Part of band structure of 118 B showing octupole correlation shown in Fig. 3.
The strength of octupole correlation is difficult to quantify experimentally and it is often inferred from the relative excitation energies of the positive and negative parity states, or from the strength of E1 transitions. This suggests that in the lighter barium isotopes the positive-and negativeparity states may form an interleaving sequence with the Istates lying lower in energy than the adjacent (I+1) + states at low spin. The observation of such a band would present a valuable insight into octupole collectivity in this region.
There is no any experimental evidence for octupole correlation in 120 Ba till now. The high spin states of very neutron deficient nucleus of 120 Ba had studied first by Cederwall et al. [12]. The yrast band of 120 Ba is extended up to spin 22ħ and one tentatively assigned negative-parity side band is observed up to spin 15ħ. Nuclear properties at high spin depends on interplay between structures based on proton and neutron h 11/2 configurations in this mass region.
Excited states in 120 Ba were populated via the 92 Mo( 32 S,2p2n) 120 Ba reaction. Due to the relatively low statistics ( 10×10 6 events) only one of the side bands could be firmly connected to the yrast cascade. The part of experimental decay scheme deduced by Cederwall et al. is shown in Fig. 1. TRS calculations have been performed for 120 Ba. In these calculations the ground state deformation is (β 2 ,γ) = (0.27,0 0 ) and the deformation of the ground band goes towards slightly negative γ-values (γ ≈-5 0 ) with increasing rotational frequency. The alignment of h 11/2 protons is predicted at ħ = 0.36 MeV, directly followed by the νh 11/2 alignment at ħ =0.42 MeV. Smith et al. have also studied the high spin states 120 Ba [13]. The high spin states have been extended up to 42ħ.
Smith et al. have also studied the high spin states 120 Ba [13]. The high spin states have been extended up to 42ħ. Smith et al. have reported that, by comparing the experimental properties of a rotational alignment to the predictions of the aligning nucleons. Alignments in the welldeformed and neutron-deficient barium isotopes are particularly interesting because both the neutron and proton Fermi levels lie within the h 11/2 subshell. The proton Fermi levels lies in the low-Ω oblate driving orbitals. As the neutron number decreases from A 130 to 120, the neutron Fermi level successively moves to lower-Ω orbitals. Furthermore, in the very neutron-deficient barium isotopes with A 120, the neutron Fermi level will lie in close proximity to the proton Fermi level, suggesting that a pninteraction may begin to influence the nuclear structure. Smith et al. have reported in their study, two alignments are observed in the heavier even-even barium isotopes, resulting in the apparent forking of the yrast band into two aligned bands. The aligned bands are assigned to have the ν(h 11/2 ) 2 and π(h 11/2 ) 2 configurations, on the basis of CSM calculations.
The neutron-deficient nucleus 122 Ba was studied in 2001 by Jiang et al. [14]. In previous reports, negative-parity side bands have been observed in some even-even nuclei in this region and some of these show evidence for octupole correlations. In the study by Jiang et al. Ref. [14], the ground-state band has been extended up to a spin 20ħ with band crossing. Also, a negative-parity side band extending up to a spin state of 19ħ is observed. States in this side band decay into those of the ground-state band via three transitions with the appearance of E1 transitions. This structure is suggestive of octupole correlations.
The portion of level scheme of 122 Ba is shown in fig. 1 by Jiang et al. The negative-parity band is connected to the ground-state band via three linking transitions with energies of 1123, 938 and 785 keV. The DCO ratio measurements suggest that the 938 keV transition linking between bands (B1) and (B2) has a stretched dipole transition character. Some calculations have predicted that octupole correlation will occur around 112 Ba. The calculations predict that the degree of ground state octupole deformation will decrease rapidly as N increases above 56, but the octupole correlations at about 6 or 8ħ in the heavier N ≈ 60 barium isotopes may also be large since the rotation will enhance the octupole correlation.
Very recently Shivcharan et al. have made an attempt to establish the unknown spin-parity of these bands using the linear polarization measurements [15]. They have also confirmed some linking transitions between negative and positive parity bands. Three tentative linking transitions 504 keV (7 -8 + ), 802 keV (5 -6 + ) and 992 keV have been confirmed. According to Shivcharan et al., the strong E1 transitions 938 keV and 787 keV shows the evidence of octupole correlations.
Level scheme reported by Mason et al. display two major structures (i.e., couples of bands of common parity linked by M1 + E2 transitions) having opposite parities, interpreted as quasi-neutron bands respectively based on the d 5/2 , g 7/2 and h 11/2 orbitals. This interpretation is suggestive of octupole correlations, in that the observation of enhanced E1 transitions linking the two structures would then signify an enhanced interaction between the d 5/2 and h 11/2 orbitals, i.e., an octupole interaction.
To check the enhancement of E1 strengths octupole correlations are expected to produce finally measured branching ratios, which in turn yielding B(E1)/B(E2) values [16]. Results are reported, in which B(E1) estimates that the nucleus 125 Ba has a prolate shape with a somewhat 'cautious' deformation of β=0.2 are also shown. A definite enhancement of E1 strengths, is observed in 125 Ba, pointing to a sizable contribution of octupole correlations to the structure of this nuclide with νd 5/2 (+g 7/2 ), νh 11/2 bands.
Experimental results by Mason et al. in case of 124 Ba are just indicative of octupole correlations [16]. B(E1)/B(E2) ratios were also determined for three levels in this nucleus, namely the J π = 11, 9 -,7ones; [16], along with B(E1) estimates corresponding to the nucleus 124 Ba having an electric quadrupole moment Q 0 =385 efm 2 . The observed enhancement of E1 strengths would not be expected if the negative-parity odd-spin band, yet interpreted as a π(d 5/2 + g 7/2 ) ⊗ πh 11/2 structure, had a purely rotational origin. Their experimental findings, indicate that octupole correlations must be included in a proper description of negative-parity states in 124 Ba at least J~11ħ.
The identification of several new E1 transitions and the measurement of B(E1)/B(E2) ratio indicate that the νd 5/2 , νg 7/2 and νh 11/2 interpretation of two major structures in 125 Ba must be integrated with the inclusion of octupole correlations. correlation in 143,144, [2]. Of particular importance will be the role of nuclear rotation in enhancing stable octupole deformation as the nuclear rotation increases in some cases and quenching (β 3 =0) of stable octupole deformation as the nuclear rotation increases in other cases as theoretically predicted. In their first report [17], new high spin states in [142][143][144][145][146] Ba and the first evidence for octupole deformation in an odd-A nucleus in this region (N = 87), 143 Ba were found. From their previous work, J.H. Hamilton et al. extracted new insights into the importance of stable octupole deformation in these nuclei [2]. The part of new level schemes for 143,144,146 Ba are shown in Fig. 3. Similar level schemes were simultaneously extracted from Eurogam II data in SF of 248 Cm by Urban et al. and Jones et al. [18,19].

B. Octupole
When reflection asymmetric stable octupole deformation occurs in odd-A nuclei, the level structures are similar to rotational bands in reflection-asymmetric molecules including two pairs of parity doublets with the same spins but opposite parities in each doublet, the simplex s=i and -i doublets [20]. Each doublet pair is intertwined by enhanced E1 transitions. The first two, E1 intertwined opposite parity bands were observed in an odd-A nucleus in this region in 143 Ba.
Jones et al. [19] found the s=i doublet pair with the same spins but opposite parities. Their newer data likewise show both parity doublets. B(E1)~1×10 -3 W.u for the s=-i doublet and ~ 0.4×10 -3 W.u for new s=i doublet, values similar to those in 144 Ba. In addition recently they find three new E1 crossing transitions and five new presumably M1 transitions between the s=i and -i bands which were not reported by Urban et al. [18]. These E1 and M1 transitions between the two doublets measure the degree of mixing of the s=i and -i doublets. The levels of 145,147 Ba are strikingly different from those of 143 Ba [2] with their ground bands having quite different structures with no evidence for stable octupole deformation. This difference between 143 Ba and 145 Ba is surprising since the 145 Ba core, 144 Ba has the strongest electric dipole moment D 0 's, most enhanced E1's and largest β 3 = 0.10 in this region. In fact, the average D 0 values are significantly larger for the higher spin states than for the lower spin states, to indicate rotation enhances the stable octupole deformation in 144 Ba in agreement with theory.

C. Octupole correlation in 122 Cs and 124 Cs
In case of the Cs isotopes as the neutron number decreases towards mid-shell N=66, the neutron Fermi level also lowers into the low Ωh 11/2 orbitals and the possibility of the residual interaction between the valence protons and the neutrons increases. The observation of nearly degenerate twin πh 11/2 ⊗ νh 11/2 bands has been cited [21,22] as evidence for the chiral symmetry breaking in these nuclei. The observation of nearly degenerate twin πh 11/2 ⊗ νh 11/2 bands has been cited [21,22] as evidence for the chiral symmetry breaking in these nuclei.
Rajesh Kumar et al. have made an attempt to establish the unknown spin-parity of observed bands using the linear polarization measurements [23]. They have also confirmed some linking transitions between negative and positive parity bands as the evidence of octupole corretion in these nuclei. High-spin states in the 122 Cs nucleus were populated using the 107 Ag( 19 F, p3n) 122 Cs fusion evaporation reaction at a beam energy of 93 MeV. Multipolarity of the de-exciting γ-rays were deduced from the observed γ−γ angular correlation measurements. DCO ratio measurement helps in unambiguous assignment of both spins and parities of nuclear states. The clover detector was used as a polarimeter to measure the polarization of the γ-rays.  The new linking transitions of 547(14 − →13 + ), 678(16 − →15 + ) and 759(18 − →17 + ) keV of E1 or E3 character between the negative-parity band B and the positive-parity band A which indicate the octupole collectivity in this nucleus. It would be of interest to explore the multipolarity of these transitions by lifetime measurements. Because of strong mixing of νd 5/2 orbital (l = 2) of negative parity band B and the νh 11/2 configuration (l = 5) of band A, there is a possibility of ∆l = 3 octupole transition between these two bands. This, however, needs to be further confirmed with the measurement of the transition probability. This is also very fortunate to obtain signature of octupole correlation when neutron number is greater than 56 i.e. N > 56. So need more appropriate theoretical discription of octupole correlation.
For 124 Cs, due to its abundant information in both lowlying and high spin states, much attention has been paid to it in systematic study and theoretical calculation. The 124 Cs nucleus was studied first time by Jing-Bin et al. by performing a 116 Sn( 11 B,3n) fusion evaporation reaction [24]. From Analysis, the five rotational sequences of 124 Cs observed and four of them are involved in figure 4. Linking γ rays, i.e., 576.2, 750.6, 749.2, 893.5, 871.0 keV between side bands (3,4) and yrast bands (1,2) are observed. The connection between the rotational bands and low-lying states fix the level energies of the yrast bands which suggests that there still exist a ~12 keV transition between the 489.8keV, 7 + level and the 478.1 keV, 5 + level (Fig.2).
The DCO ratio of the 270.0kev γ-ray depopulating the 270.0keV level is deduced to be ~1.05, which limits this ray to be a quadrupole transition. The large intensity of the 270.0keV γ-ray in the prompt coincidence measurement fixes it to have the E2 character. Thus, the 270.0keV level is assigned as 3 + . The missing ~31 keV transition should have an E1 character. This nucleus was studied later by Yang Dong et al. and the part of level scheme from their work is shown in Fig. 2. The key of the problem is whether there are linking transitions between bands 1 and 2. Yang Dong et al. have obtained plenty of information in their work proves that they do exist: the first evidence is the coincidence relation observed between the linking and intraband transitions. From the level scheme. in figure 2, 266.7(8 − → 7 + ), 412.2(9 − → 8 + ), 576.2(10 − → 9 + ), 750.6(11 − → 10 + ), 749.5(12 − → 11 + ), 893.5(13 − → 12 + ), and 871.0(14 − → 13 + ) keV transitions connecting bands 1 and 2 can be seen clearly. The second evidence is three linking transitions of 529.4(9 − → 8 + ), 867.9(11 − → 10 + ) and 986.7(13 − → 12 + ) keV found in [25] connecting bands1 and 3. Similar linking transitions have been reported in the isotope 122 Cs [23] providing the fourth evidence which is from the systematic study. Considering the facts mentioned above, the linking transitions have been proved to exist. Then level energies of band 1 are fixed by its connections with bands 2 and 3.
Moreover, a new cascade sequence denoted as band 4 is established in Yang Dong et al.'s work, its decouple character and connection with band 3 indicate that it most likely corresponds to the unfavored signature partner of the πh 11/2 ⊗ νd 3/2 band in figure 2. The E1 linking transitions between the yrast and πh 11/2 ⊗ ν(d 5/2 ,g 7/2 ) bands has been proposed. Such enhanced E1 transitions linking alternateparity bands are the experimental fingerprint of octupole correlations. Very recently work, K. Selvakumar et al., have found evidence for octupole correlation in 124 Cs [26]. Lifetime have been measured using Doppler Shift Attenuation Method (DSAM) for the negative parity, πh 11/2 ⊗ ν(g 7/2 d 5/2 ) and the positive parity, πh11/2 ⊗ νh 11/2 bands of 124 Cs. The B(E1) transition rates have been deduced for the linking transitions between the bands with the above configurations and a possibility of octupole correlation is discussed. The linking transitions proposed in the earlier work [27] was confirmed by Selvakumar et al. [26]. The B(E1) rates for the linking transitions connecting negative parity (band 3) and positive parity (band 1) bands have been deduced. The measured B(E1) rates are of the order of 10 -4 W.u. and are comparable to those in 117 Xe [28], in which octupole correlations were observed. An enhancement in B(E1) rates has been observed with increasing spin, indicating existence of octupole correlations in 124 Cs.

D. Octupole correlation in 141,143 Cs
The theoretical Calculations of Cwiok et al. [29] suggested that the neutron-rich Cs isotopes have an octupole deformation in their ground states. The previous studies from Urban et al. on these nuclei [30], have identified yrast excitations in 141 Cs, 143 Cs, and 145 Cs, interpreted as either decoupled 141,143 Cs and strongly coupled 145 Cs configurations, due to valence protons in the πg 7/2 and πd 5/2 orbitals.
One of the measurement from Urban et al. [31] has uncovered many new γ-transitions in 141 Cs and 143 Cs, extended their excitation schemes and identified levels corresponding to octupole excitations. Fig. 3 shows the level scheme of 141 Cs, as obtained from the work of Urban et al. [31]. They added ten new tentative levels in the level scheme, but enable to confirm the 1577.2 keV level reported, because their data suggest that the 726.7 keV line reported feeds the 1488.8 keV level, rather than the 850.7 keV level. They took spin and parity 7/2 + for the ground state and 5/2 + for the 105.7 keV level from the literature [44]. Since no half-life longer than 10 ns was seen, the quadrupole transitions observed in 141 Cs and 143 Cs are E2. The total conversion coefficient for the 105.7 keV transition, found from the intensity balance, is α T =1.5 (2) . This value can be compared to the theoretical values of 0.2, 0.9 and 1.7 for the E1, M1, and E2 multipolarities, respectively, confirming the M1 + E2 character of the 105.7 keV transition. Fig. 3 shows the level scheme of 143 Cs, as obtained in the work of Urban et al., [31].
They added ten new tentative levels in the level scheme, but enable to confirm the 1577.2 keV level reported, because their data suggest that the 726.7 keV line reported feeds the 1488.8 keV level, rather than the 850.7. keV level. They took spin and parity 7/2 + for the ground state and 5/2 + for the 105.7 keV level from the literature [44]. Since no half-life longer than 10 ns was seen, the quadrupole transitions observed in 141 Cs and 143 Cs are E2. The total conversion coefficient for the 105.7 keV transition, found from the intensity balance, is α T =1.5 (2) . This value can be compared to the theoretical values of 0.2, 0.9 and 1.7 for the E1, M1, and E2 multipolarities, respectively, confirming the M1 + E2 character of the 105.7 keV transition. Fig. 3 shows the level scheme of 143 Cs, as obtained in the work of Urban et al., [31]. To the scheme reported in Refs. [30,31], they add 17 new, non yrast levels, based on the observed coincidence relation. They also add a new band based on the 1182.3 keV level as shown in Fig. 3. An important result of this work is an E1 multipolarity assignment to the 399.6 keV, 523.5 keV, and 628.8 keV transitions, based on the angular correlation and linear polarization. This allows the negative-parity assignment to the bands based on the 816.6 keV and 872.6 keV levels. With a negative-parity assignment to these new bands in 143 Cs a parity-doublet-like structure is found in this nucleus. It is expected that in nuclei with octupole deformation, one should observe electric dipole moments D 0 significantly larger than in nuclei without octupole deformation. The newly found D 0 value in 143 Cs and tentative D 0 value in 141 Cs are significantly smaller than in their Ba isotones, 142 Ba and 144 Ba, respectively. The decrease of octupole effects when approaching the Z=50 line is expected as a consequence of the existence of a shell gap at Z=50, have shown that this is so, when approaching the Z=50 line along the N=85 line. A similar scenario is suggested for the N=86 isotones by this data on 141 Cs.

E. Octupole correlation in 114 Xe and 117 Xe
Angelis et al. [32] have measured gamma ray linear polarization and picoseconds lifetimes for levels in the neutron deficient nucleus 114 Xe using the EUROBALL IV spectrometer and the cologne plunger device. They unambiguously determined the electromagnetic character of mass region. In the vicinity of the N=Z line enhanced polarization can be expected, due to the presence of an isoscalar proton and neutron (π(ν)d 5/2 ν(π)h 11/2 ) 3 term. These dynamical correlations are not taken into account in the mean-field approach. They suggested that such coherent proton-neutron correlations are responsible for the exceptional strong enhancement of the octupole collectivity which is encountered in their study of 114 Xe. A part of level scheme for the 114 Xe nucleus, relevant to this work, is shown in Fig.  4. The high efficiency of the EUROBALL array for high energy γ rays has allowed the identification of two E3, γtransitions of 1549.1(5) and 1623(1)keV, respectively, connecting the 5 − level at 2000 keV to the 2 + at 450.1 keV and the 3at 1623 keV to the ground state.
In the presence of low lying octupole correlation, a large E1 moment may arise in the intrinsic frame due to shift between center of mass and center of charge. Such a dipole moment manifests itself by enhanced electric dipole transitions between members of opposite parity rotational bands, hence these E1 transition are considered as the most prominent experimental feature pointing to existence of octupole correlation, especially for those nuclei having no octupole minimum deep enough on its potential energy surface. Such E1 transitions have been seen in 114 Xe [28] and 110 Te [33]. The previously known υh 11/2 bands (labeled 1,2) and υg 7 [1,34], only the nuclei with N and Z very close to 56 in this region are expected to possess octupole collectivity. The neutron number of 117 Xe differs from 56 by 7 and no octupole softness was predicted for this nucleus. The experiment observation of octupole correlations in 117 Xe is not in agreement with the theoretical calculations and calls for further theoretical studies of octupole effects in this region.

IV. SUMMARY AND CONCLUSION
The theoretical and experimental evidences of octupole correlation of atomic nuclei like Ba, Cs and Xe have been reviewed. The linking transitions between positive and negative parity bands have seen which the evidence for octupole correlation in these nuclei is. In the case of barium, a negative parity band has been observed in all of the eveneven barium isotopes with A˂132. The observation of this low lying negative-parity band, decaying by relatively strong E1 transitions is proposed as possible evidence for octupole correlations. The calculations predict the deformation will be a maximum for 118 Ba which establish a lower limit on the trend of increasing deformation in the neutron-deficient barium isotope. In the case of neutron deficient nucleus 120 Ba even this nucleus have Z=56 there is no any discussion about octupole correlation for this nucleus. So it needs further investigation. The earlier investigations for the level structure of 122 Cs have not reported any signature for octupole but in the later work Rajesh et. al., have made an attempt to establish the unknown spin-parity of these bands using the linear polarization measurement. So it would need more appropriate theoretical description for octupole correlation. One conclude that up to N=86 and the Z=50 gap exist lower limit, in the proton number of the region of octupole deformation but in the neutron rich lanthanides is at Z=55. In the case of 124 Cs, octupole correlation is not predicted for this nucleus, but very recently the octupole correlation was confirmed in 124 Cs. It still remain an open question where is the border line for octupole deformation. Now in the case of Xe, according to theoretical studies only the nuclei with N and Z very close to 56 in this region are expected to possess octupole collectivity, the neutron number in 117 Xe differs from 56 by 7 and no octupole softness was predicted. But experimental observation of octupole correlation in 117 Xe is not in agreement with the theoretical calculations and calls for further theoretical studies of octupole effects in this region. This work highlights the absence of any satisfactory conclusion for octupole correlation and reiterates the need for calculations to be performed for the better results for octupole correlation in this mass region.