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The $^{137}\mathrm{La}$ nucleus was populated by the reaction $^{130}\mathrm{Te}(^{11}\mathrm{B}, 4n$) at 40-MeV beam energy and the lifetime of the $11/{2}^{\ensuremath{-}}$ state at $1004.6\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$ was measured using a hybrid array of HPGe clover and ${\mathrm{LaBr}}_{3}$(Ce) detectors by electronic fast-timing technique, providing the value ${T}_{1/2}=263\ifmmode\pm\else\textpm\fi{}12\phantom{\rule{0.28em}{0ex}}\mathrm{ps}$. The reduced transition probability $B(E3)=23.3\ifmmode\pm\else\textpm\fi{}2.4\phantom{\rule{0.28em}{0ex}}\mathrm{W}.\mathrm{u}.$ is found to be significantly larger compared to the values observed in lighter odd-$A$ La isotopes. The experimentally determined $B(E3)$ value is compared with theoretical calculations of random-phase approximation which explains the enhanced transition probability to be arising from higher contribution of the ${g}_{9/2}$ orbital to the proton transition density.

High-spin excited states of $^{135}\mathrm{Pm}$ have been investigated using the $^{107}\mathrm{Ag}(^{32}\mathrm{S}$, $2p2n$) reaction at 145-MeV beam energy. Three negative-parity bands have been investigated up to $\ensuremath{\sim}9.0\ensuremath{-}$, $7.6\ensuremath{-}$, and $6.9\ensuremath{-}\mathrm{MeV}$ excitation energies with spin parities $(55/{2}^{\ensuremath{-}})$, $(49/{2}^{\ensuremath{-}})$, and $(47/{2}^{\ensuremath{-}})\phantom{\rule{4pt}{0ex}}\ensuremath{\hbar}$, respectively. The experimental results have been interpreted using the triaxial projected shell model. It is shown that the observation of the parallel band structures can be explained in terms of crossing of two $s$ bands with the yrast band, which is a rare phenomenon for an odd-$A$ nucleus. Further, the lifetimes of levels in yrast band have been extracted using Doppler shift attenuation method. The evaluated $B(E2)$ values of yrast states show the loss of collectivity at higher spin, attributed to the alignment process.

We have characterized a Cerium doped Lanthanum Bromide (LaBr3(Ce) ) crystal coupled with the position-sensitive photo-multiplier system for the gamma-ray imaging application. One can use this detector set-up for the scanning of high purity germanium detectors for pulse shape analysis in gamma-ray spectroscopy experiments and the image formation of an object by Compton back-scattering . The sensor has been tested for energy, timing and position information of the gamma-rays interacting within the detector crystal. The GEANT4 simulation results are consistent with the experimental results. We have reconstructed the image of irradiation spots in different positions throughout the detector crystal. Position resolution is found to be around 3.5 mm with the 2 mm collimated gamma-rays. The 2-d image of hexagonal Bismuth Germanate (BGO) crystal and a cylindrical LaBr3(Ce) crystal have been reconstructed in coincidence technique. The performance of the detector for imaging application has been investigated by coincidence technique in GEANT4 simulation and compared with the experimental data. We have reconstructed the 2-d images of objects with various geometrical shapes by Compton back-scattered events of the gamma-rays. This position-sensitive detector can be used as an absorber of a Compton camera for the image reconstruction of an extended radioactive source. One can also use this kind of set-up as in radiation imaging and many other applications where the energy and source position of the gamma-ray is the main interest.

We report measurement of the $g$-factor for the ${11/2}^{\ensuremath{-}}$ isomeric state at 535 keV in $^{133}\mathrm{La}$, employing the time differential perturbed angular distribution technique (TDPAD). This isomer was populated in the reaction $^{126}\mathrm{Te}(^{11}\mathrm{B}$, $4n)^{133}\mathrm{La}$ at beam energy of 52 MeV. From the observed nuclear spin precession, analysed through combined, magnetic dipole and electric quadrupole hyperfine interactions, we obtain the $g$ factor for the $11/{2}^{\ensuremath{-}}$ state as $g=1.16\ifmmode\pm\else\textpm\fi{}0.07$. In addition, this analysis provides the spectroscopic quadrupole moment $|Q|=1.71\ifmmode\pm\else\textpm\fi{}0.34\phantom{\rule{3.33333pt}{0ex}}b$, yielding the deformation parameter $\ensuremath{\beta}=0.28\ifmmode\pm\else\textpm\fi{}0.10$. Further, we have performed theoretical calculations using the large-scale shell model and the Monte Carlo shell model. The results successfully describe the low-lying levels and the band structures of $^{133}\mathrm{La}$, and the calculated $g$ factor compares well with the values obtained from our experiment. The dominant configuration of $11/{2}^{\ensuremath{-}}$ isomeric state in $^{133}\mathrm{La}$ is inferred to be $\ensuremath{\pi}({h}_{11/2})\ensuremath{\bigotimes}^{132}\mathrm{Ba}({0}^{+})$.

The low-lying negative parity states in the 133Ba nucleus have been investigated using the 124Sn(13C, 4nγ)133Ba reaction at E l a b = 48 MeV. With the addition of new γ-transitions, n ω = 0 , 1 , 2 wobbling bands were identified in this nucleus. The angular correlations and linear polarization measurements have been performed to confirm the spin and parity of the states. Predominant E2 character was obtained for the inter-linking Δ I = 1 transitions between the successive phonon ( Δ n ω = 1 ) wobbling bands. The transverse nature of the wobbling bands is concluded on the basis of observed decreasing behavior of the wobbling frequency with increasing spin. The quasiparticle triaxial rotor model calculations are found to be in agreement with the experimentally determined wobbling frequency and the transition probability ratios. This letter reports the first observation of transverse wobbling mode associated with a hole-like quasiparticle.

The intermediate and high-spin states of the $^{134}\mathrm{Ba}$ nucleus have been investigated up to spin ${I}^{\ensuremath{\pi}}=({20}^{\ensuremath{-}})$ using the $^{124}\mathrm{Sn}(^{13}\mathrm{C}, 3n)^{134}\mathrm{Ba}$ reaction at a beam energy of 48 MeV. The ${R}_{\mathrm{DCO}}$ and polarization asymmetry measurements were carried out to assign the spin and parity of the levels. Three ($\mathrm{\ensuremath{\Delta}}I=2$) negative parity bands were studied above the 1985.9 keV level having spin ${I}^{\ensuremath{\pi}}={5}^{\ensuremath{-}}$. The two quasiparticle $\ensuremath{\nu}[{h}_{11/2}\ensuremath{\bigotimes}({s}_{1/2}/{d}_{3/2})]$ configuration has been assigned to these bands based on the systematics of the $\mathrm{Ba}$ (even-$N$) isotopes and similarity in the behavior of signature splitting and $B(M1)/B(E2)$ ratios. Further, two ($\mathrm{\ensuremath{\Delta}}I=1$) dipole bands have also been observed starting at the 5677.9 and 5284.5 keV levels with spin ${I}^{\ensuremath{\pi}}={14}^{\ensuremath{-}}$ and ${15}^{+}$, respectively. The configuration of these bands was suggested from the systematics of the similar structure in the neighboring nuclei. Tilted axis cranking (TAC) calculations were carried out using the four quasiparticle $\ensuremath{\pi}[{h}_{11/2}({g}_{7/2}/{d}_{5/2})]\ensuremath{\bigotimes}\ensuremath{\nu}{[{h}_{11/2}]}^{2}$ and $\ensuremath{\pi}[{h}_{11/2}({g}_{7/2}/{d}_{5/2})]\phantom{\rule{4pt}{0ex}}\ensuremath{\bigotimes}\phantom{\rule{4pt}{0ex}}\ensuremath{\nu}[{h}_{11/2}{d}_{3/2}]$ configurations for bands D1 and D2, respectively. The TAC calculations and systematic studies of similar structures in the neighboring $N=78$ isotones suggest that the dipole band (D1) observed at 5677.9 keV level may have the magnetic rotation character.

Lifetimes of excited states of the ground-state rotational band in the $^{136}\mathrm{Sm}$ nucleus have been measured up to ${I}^{\ensuremath{\pi}}={20}^{+}$ using the Doppler-shift attenuation method. The states were populated in the reaction $^{107}\mathrm{Ag}$($^{32}\mathrm{S}$, $1p2n$) at 145-MeV beam energy and the $\ensuremath{\gamma}$ rays emitted from the excited states were detected using the Indian National Gamma Array at the Tata Institute of Fundamental Research, Mumbai. The extracted transitional quadrupole moments indicate a reduction of collectivity with increasing spin after the band crossing. The results have been compared with the predictions of the cranked shell model as well as the triaxial projected shell-model calculations and indicate that the nucleus evolves from prolate $\ensuremath{\gamma}$-soft to a stable triaxially deformed shape after the first and the second crossing involving $\ensuremath{\pi}{h}_{11/2}^{2}$ and $\ensuremath{\pi}{h}_{11/2}^{2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}^{2}$ configurations, respectively.

Background: There has been a considerable interest focused on the study of enhancement or suppression in collectivity of the excited ${2}_{1}^{+}$ states in stable Sn isotopes. Independent measurements of Coulomb excitation cross sections and ${2}_{1}^{+}$ level lifetimes report discrepant transition probabilities. Existing estimates for ${2}_{1}^{+}$ lifetime indicate reduced collectivity.Purpose: A reexamination of lifetime of the ${2}_{1}^{+}$ state in the most abundant $^{120}\mathrm{Sn}$ isotope is thus warranted. The same has been carried out in the present work and the result has been used to determine the transition probability as an indicative of the underlying collectivity.Methods: Low-lying levels in the vibrational $^{120}\mathrm{Sn}$ nucleus have been excited by inelastic scattering with $^{32}\mathrm{S}$ beam at ${E}_{\mathrm{lab}}=120$ MeV. Level lifetime measurements have been carried out using the Doppler shift attenuation method, wherein the Doppler affected $\ensuremath{\gamma}$-ray peaks have been analyzed using updated methodologies.Results: From the measured lifetime of the ${2}_{1}^{+}$ state (${E}_{x}=1171$ keV) in $^{120}\mathrm{Sn}, {\ensuremath{\tau}}_{{2}_{1}^{+}}=0.{863}_{\ensuremath{-}0.036}^{+0.029}$ ps, a value of $B(E2;{0}_{\mathrm{g}.\mathrm{s}.}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})=0.{215}_{+0.009}^{\ensuremath{-}0.007}$ is deduced. An estimate of the ${4}_{1}^{+}$ (feeder) level lifetime, ${\ensuremath{\tau}}_{{4}_{1}^{+}}=1.{77}_{\ensuremath{-}0.089}^{+0.084}$ ps, is also reported from lineshape analysis of $\ensuremath{\gamma}$ rays in cascade.Conclusions: An enhancement in collectivity for the ${2}_{1}^{+}$ state is confirmed, following an improved determination of the level lifetime, with reduced uncertainties. The excited ${2}_{1}^{+}$ state is also found to have a nonvanishing moment of inertia, suggesting anharmonic nature of quadrupole vibrations.

High-spin states in Zr89 were populated in the Se80(C13,4n) reaction, and γ-ray coincidences were measured using the Indian National Gamma Array. The level scheme of Zr89 has been extended up to spin I=49/2 with the observation of a new dipole band. Directional correlation and polarization asymmetries of the γ rays have been measured to determine spin and parity of the levels. Line shapes of several transitions have been analyzed to determine lifetimes of the levels. Possible configurations of the band have been discussed using the cranked Nilsson-Strutinsky model. The calculations suggest a triaxial shape of the nucleus at high spins, and the band may represent rotation of the nucleus about the longest axis.

Evaporated α-spectra have been measured in coincidence with low energy discrete γ-rays from residual nucleus 68Zn populated by αn evaporation from compound nucleus 73Ge produced in the reaction 64Ni(9Be,αn)68Zn at E ( 9 Be) = 30 MeV. Low energy γ-gated α-particle spectra, for the first time, have been used to extract the nuclear level density (NLD) for the intermediate 69Zn nucleus in the excitation energy range of E ≈ 4-20 MeV. The slope of present NLD data as a function of excitation energy for 69Zn matches nicely with the slope determined from RIPL estimates for NLD at low energies and the NLD from neutron resonance data at neutron separation energy S n . The extracted inverse NLD parameter (k = A/ a ˜ ) has been used to determine the nuclear level density parameter value a at neutron separation energy S n for 69Zn. The cross section of 68Zn(n,γ) capture reaction as a function of neutron energy is then estimated employing the derived a ( S n ) in the reaction code TALYS. It is found that the estimated neutron capture cross section agrees well with the available experimental data without any normalization. The present result indicates that experimentally derived nuclear level density parameter can constrain the statistical model description of astrophysical capture cross section and optimize the uncertainties associated with astrophysical reaction rate.

Excited states of the $^{61}\mathrm{Ni}$ ($Z=28,N=33$) nucleus have been probed using heavy-ion-induced fusion evaporation reaction and an array of Compton suppressed germanium (clover) detectors as detection system for the emitted $\ensuremath{\gamma}$ rays. Seventeen new transitions have been identified and placement of six transitions have been modified with respect to the previous measurements, following which the level scheme of the nucleus has been extended up to an excitation energy ${E}_{x}\ensuremath{\approx}7$ MeV and spin $\ensuremath{\approx}10\ensuremath{\hbar}$. Higher excitations involving the ${g}_{9/2}$ orbital in the $fpg$ model space have been established. The experimental results on the level structure of the nucleus have been interpreted in the light of large basis shell model calculations that lead to an understanding of the single particle configurations underlying the level structure of the nucleus. The comparison can be suggestive of further refinements in the shell model interactions for better overlap of the theoretical results with the experimental data.

The g factor of an isomeric state at 2738 keV in La135 has been measured by time differential perturbed angular distribution technique. This isomer was populated in the reaction Te128(B11, 4n)La135 at beam energy of 52 MeV. We performed the large-scale shell-model (LSSM) calculations which successfully describe the low-lying levels and band structures of La135. The measured value of the g factor,−0.049(3), has been compared with the LSSM result to firmly assign the configuration of the isomeric state. The major configuration of 23/2+ state is π(d5/2)⊗ν(h11/2)−2.

Excited states of the $^{64}\mathrm{Cu}\phantom{\rule{4pt}{0ex}}(Z=29,N=35)$ nucleus have been probed using heavy-ion-induced fusion evaporation reaction and an array of Compton-suppressed Clovers as detection system for the emitted $\ensuremath{\gamma}$ rays. More than 50 new transitions have been identified and the level scheme of the nucleus has been established up to an excitation energy ${E}_{x}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}\phantom{\rule{4pt}{0ex}}6$ MeV and spin $\ensuremath{\sim}10\ensuremath{\hbar}$. The experimental results have been compared with those from large-basis shell-model calculations that facilitated an understanding of the single-particle configurations underlying the level structure of the nucleus.

The high-spin states in $^{133}\mathrm{Cs}$, populated using the reaction $^{130}\mathrm{Te}(^{7}\mathrm{Li},4n)$ with 45-MeV beam energy, have been extended up to an excitation energy of 5.265 MeV using the Indian National Gamma Array. The observed one- and three-quasiparticle bands in $^{133}\mathrm{Cs}$, built on the $\ensuremath{\pi}{h}_{11/2},\phantom{\rule{0.28em}{0ex}}\ensuremath{\pi}{g}_{7/2}$, $\ensuremath{\pi}{d}_{5/2}$; and ${(\ensuremath{\pi}{g}_{7/2}\ensuremath{\pi}{d}_{5/2})}^{1}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}2}$ configurations, respectively, have similar structure as seen in the lighter odd-$A$ Cs isotopes. The experimental level scheme has been compared with the large-scale shell model calculation without truncation using the $jj55pna$ interaction, showing a good agreement for both positive- and negative-parity states.