Lifetimes of the 15/2-1 and 13/2-1 levels in 129Sn have been measured using gamma -gamma fast timing technique which come out to be 10(3) ps and 6(4) ps, respectively. The excited states were populated through internal transition decay of higher lying mu s isomers in 129Sn produced as fission fragments and mass separated by the Lohengrin separator at Institut Laue-Langevin. The generalized centroid difference method was applied with four LaBr3(Ce) detectors, placed at the focal plane of the separator. The measured lifetimes and absolute transition probabilities are discussed in the light of large scale shell model calculations to interpret the single particle configurations and their mixing.

A positive parity sequence of ΔI=2 γ transitions has been identified above Iπ=9/2+ state (Ex=2019 keV) in 115Sb through in-beam γ ray spectroscopic technique. Rotational features of this sequence are found similar to a low-K decoupled band. Observation of this newly identified low-K decoupled band, along with the earlier reported strongly coupled high-K band in this nucleus, provides the first experimental evidence for prolate-oblate shape coexistence associated with g9/2 proton-hole configuration around Z=50 shell closure. Experimental results are reproduced reasonably well in the frameworks of the projected shell model and the total Routhian surface calculations.

Lifetimes of the $15/{2}_{1}^{\ensuremath{-}}$ and 13/${2}_{1}^{\ensuremath{-}}$ levels in $^{129}\mathrm{Sn}$ have been measured using $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ fast timing technique which come out to be 10(3) ps and 6(4) ps, respectively. The excited states were populated through internal transition decay of higher lying $\textmu{}\mathrm{s}$ isomers in $^{129}\mathrm{Sn}$ produced as fission fragments and mass separated by the Lohengrin separator at Institut Laue-Langevin. The generalized centroid difference method was applied with four ${\mathrm{LaBr}}_{3}$(Ce) detectors, placed at the focal plane of the separator. The measured lifetimes and absolute transition probabilities are discussed in the light of large scale shell model calculations to interpret the single particle configurations and their mixing.

The excited states of odd–odd ^54 Mn ( Z=25, N=29 ) nucleus have been investigated using the fusion evaporation reaction ^55 Mn( α , α n) ^54 Mn at the beam energy of 34 MeV. A new and improved level scheme of ^54 Mn has been proposed in this work with the placement of 22 new γ -ray transitions. Spin and parity (J ^π ) of most of the levels in the revised level scheme have been firmly assigned. The placement of some of the already known γ rays in the level scheme and J ^π assignments of some of the levels reported earlier have also been revised. The new level scheme, which has been extended up to ∼ 6 MeV, provides new insight and interesting structural aspects of the generation of high angular momentum in this odd–odd Mn isotope with neutron number ( N=29 ) just above the N=28 shell gap. Three octupole-phonon-coupled negative parity states have been identified for the first time in this nucleus. E 3 transitions have also been observed to decay from these states. Shell model calculations with two different interactions i.e. kb3gpn and gx1pn have been performed which well reproduced the low-lying, few-particle states but fail to reproduce the higher-lying multi-particle states. These higher-lying states have been understood as resulting from collective excitations. An oblate minimum obtained from the Total Routhian Surface calculations provides support to this conjecture.

Lifetimes have been measured for the low-lying yrast levels of Te-130,Te-132 using gamma - gamma fast timing methods. The excited states were populated in beta(-) and IT decay of fission fragments, mass-separated by the Lohengrin separator at Institut Laue-Langevin. Four LaBr3(Ce) detectors, placed at the focal plane of the spectrometer, were used for the gamma -gamma fast timing measurement. Lifetimes of mu s isomers were measured using coincidence of an ionization chamber with two Clover HPGe detectors. Themeasured lifetimes and absolute transition probabilities are discussed in the light of systematics with the neighboring nuclei. Large basis shell model calculations have been performed to interpret the level structure and transition probabilities in these even mass Te isotopes.

Lifetimes are measured for low lying states of $^{150}\mathrm{Sm}$, populated from ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{150}\mathrm{Pm}$ produced through $(p,n)$ reactions with a $^{150}\mathrm{Nd}$ target. The VENTURE array comprising of eight fast ${\mathrm{CeBr}}_{3}$ detectors is used for lifetime measurement with $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ fast timing technique. The lifetime of ${0}_{3}^{+}$ level of $^{150}\mathrm{Sm}$ is measured for the first time to be 36(10) ps. The ${0}_{3}^{+}$ level is found to have enhanced decay strengths to the ${K}^{\ensuremath{\pi}}={0}_{2}^{+}$ structure compared with ${K}^{\ensuremath{\pi}}={0}_{1}^{+}$. A high ${\ensuremath{\rho}}^{2}(E0)$ strength for the ${0}_{3}^{+}\ensuremath{\rightarrow}{0}_{2}^{+}$ decay confirms shape coexistence and shape mixing in $N=88\phantom{\rule{4pt}{0ex}}^{150}\mathrm{Sm}$.

The nuclei around N = 90 and with proton number close to the Z = 64 subshell closure are known to exhibit deformed structures. A rapid evolution of shapes and deformation are experimentally identified in these nuclei [1,2]. The deformed band structures could be characterized with stable prolate deformation in the ground state along with the presence of octupole shapes at very low excitation [3,4]. The presence of deformation driving orbitals for the mid-shell neutrons along with the J = 3 orbitals for protons, gives rise to the possibility of different degree of deformation to the nuclear surface in this mass region. In addition, the vibrational structures are also observed in these nuclei around stable quadrupole [5] as well as octupole shapes [6]. Till date, the lifetimes have been measured in N = 88 Sm, mostly by using neutron excitation with Doppler Shift and Grid techniques. The measured lifetimes of the negative parity levels [7-9] strongly confirms the existence of octupole shapes and correlation in this nucleus as observed from other spectroscopic results. Another important aspect is the lifetime of the 03 + level that has displayed interesting structure phenomenon in the neighboring Sm nuclei [10]. The literature survey of lifetime data in 150 Sm indicates the need for lifetime measurements in several low lying levels to study the evolution of nuclear structure. In the present work, the lifetime measurement has been attempted in 150 Sm using gamma-gamma fast timing spectroscopy with VENTURE array [11] at VECC, Kolkata. The obtained lifetimes and the corresponding transition probabilities have been systematically compared with those known in the neighboring nuclei. Experiment:

The even-even Xe isotopes in the west of N = 82 neutron shell closure are known to display the transitional behavior from vibrational to rotational as one moves away from the shell closure [1,2,3]. These nuclei around 132 Sn also show octupole correlation, the strength of which decreases with the filling of neutron pairs till N = 82 [4]. The octupole correlation in this mass region may arise either from proton as well as neutron J = 3 orbitals as both the nucleon occupy the same subshell space. Although in most of the cases the coupling between the proton orbitals are found to be responsible, the coherent contribution of both protons and neutrons may bring in enhancement of octupole correlation and B(E3) strengths [5]. The odd-A isotopes of neutron rich Xe around 132 Sn are comparatively less studied and may be interesting in delineating the role of a unpaired neutron in the structure of these nuclei. The lifetime measurements for the low lying states are thus important to explore these rarely studied nuclei, mainly through decay of fission fragments. The experimental data on both 133,135 Xe were limited mainly to beta decay and light ion induced reaction [6]. Recently, multi-nucleon transfer reactions have been used to study the high spin level structure and isomers in these nuclei [7,8]. Level lifetimes are not known for any excited levels in these two nuclei except few long lived isomeric levels, viz., 11/2 and 23/2 . Such lifetime data, especially for the low lying levels developed with the excitation of few neutron holes are of extreme importance to understand the nuclear structure around double shell closure of 132 Sn. In the present work, the level lifetimes for two odd-A Xe nuclei, 133,135 Xe, has been aimed from the decay of radio-chemically separated 133,135 I fission products.