The structure of the unnatural parity bands in 49V, populated through the 48Ti(4He, 2np)49V reaction induced by a 48 MeV α beam, have been studied utilizing the Indian National Gamma Array (INGA) facility. The level scheme up to Jπ = 19/2+ have been confirmed using the results obtained from relative intensity, directional correlation, and linear polarization measurements. Lifetimes of six excited states have been measured using the Doppler shift attenuation method (DSAM). The experimental findings have been compared with the results obtained from shell model calculations.

The low-lying level structure of 80Se was investigated via the 76Ge(9Be,2p3n) reaction at Elab ≈ 31 MeV using a Compton-suppressed HPGe clover array, and level lifetimes were measured with the Doppler-shift attenuation method. Measured excitation energies and B(E2) transition strengths are reasonably well reproduced by Interacting Boson Approximation (IBA) calculations. The observed excitation-energy and transition-strength patterns associated with the σ=5 and σ=3 representations, together with candidate members of the σ=1 representation, exhibit pronounced O(6)-like collective behavior in this five-boson system. The combined experimental observables and finite-boson IBA calculations indicate a surprisingly good correspondence with O(6) expectations for these selected collective structures. At the same time, the presence of low-lying 02+ and 23+ states that are not consistently accommodated within the same classification, together with a finite B(E2;03+→21+) strength, demonstrates that the O(6) limit does not provide a complete description of the low-energy spectrum. We therefore interpret the present results as evidence for pronounced O(6)-like collective structures embedded within a more complex nuclear structure of 80Se.

Low-and intermediate-spin negative-parity band structures have been investigated in the 82Kr nucleus using the fusion-evaporation reaction 76Ge (9Be, 3n) at ELab approximate to 31 MeV. Lifetimes of the states of interest in 82Kr have been measured using the Doppler shift attenuation method with the help of the Indian National Gamma Array, and the parity of the states has been confirmed from polarization measurements. The deduced B(M1) and B(E2) values from the lifetime measurements in comparison with the particle rotor model and the total Routhian surfaces calculations reveal that the bands DB1 and DB2 are based on the collective oblate and prolate deformed core, respectively. The enhanced electric dipole strengths, B(E1)s, and dipole moments, |D0|s, for the parity-changing transitions connecting the negative-parity bands DB1 and DB2 to the ground-state positive-parity band QB1 ensure the octupole correlation in 82Kr.

The K pi = 0+ and K pi = 4+ bands of 52Cr, populated through the 51V(4He, 2np) 52Cr reaction with a 45 MeV 4He beam, have been studied using the Indian National Gamma Array (INGA) facility. The level scheme has been verified utilizing the results of intensity, directional correlation, and linear polarization measurements. Lifetimes of a few excited states in the observed bands have been measured/remeasured using the Doppler shift attenuation method (DSAM). Large basis shell model calculations have been performed within the f p valence space to understand the microscopic origin of these bands. Structural evolution and K mixing throughout the bands in 52Cr have been investigated using the calculated quadrupole moments (Qs) and the results obtained from one-nucleon transfer spectroscopic factor calculations.

We report on experimental evidence for a new, second tetrahedral band in 152 62Sm90. It was populated via fusion evaporation reaction 150Nd(alpha, 2n) 152Sm, employing a 26 MeV beam of alpha particles from the K-130 cyclotron at the Variable Energy Cyclotron Centre, Kolkata, India. The newly observed possible mixed parity sequence with absence of E2 and strong indication of E3 transitions is consistent with the spectroscopic criteria for a tetrahedral-symmetry rotational band that could be constructed from the allowed spin-parity assignments. This structure differs from the structure of the band previously found in the same nucleus, the new one manifesting tetrahedral symmetry not accompanied by the octahedral one. Our new experimental results are interpreted in terms of group representation theory and the collective nuclear-motion theory of Bohr. We propose to generalize the notion of the tetrahedral vibrational bands and believe that our new experimental results support a number of theory predictions related to nuclear tetrahedral symmetry published earlier and bring a new light into the issue of spontaneous symmetry breaking in heavy nuclei.

Spectroscopic properties of the unnatural-parity states of 43Ca populated through the 27Al(19F,2pn)43Ca reaction at 68 MeV beam energy, have been investigated using the Indian National Gamma Array (INGA) facility. The level scheme has been extended up to the J pi = 25/2+, the band-terminating state corresponding to pi(1d3/2)-1(1 f7/2)1 circle times nu (1 f7/2)3 configuration, by adding two new levels and six new transitions to the existing level scheme. The spin-parity assignments for the observed levels were done by RDCO, RADO, and linear polarization measurements. The multipole mixing ratios (delta) for most of the transitions were measured. Large basis shell-model calculations were carried out to explain the microscopic origin of observed levels. Interplay between single-particle and collective mode of excitations in the positive parity levels has also been discussed.

Results of our experimental study of the 24Mg(p,γ)25Al resonance reaction at E=plab223 keV are presented. The proton beam energy is varied from 220 to 265 keV. An evaporated Mg target with thick Ta backing is used. We remeasure a mean lifetime of τ=6.04−2.65+3.03 fs for the E=x2485.3 keV level of 25Al, using Doppler shift attenuation (DSA) method. Three most successfully used empirical effective interactions developed for the sd shell by Wildenthal (w), Chung-Wildenthal (cw) and Preedom-Wildenthal (pw), are utilized to calculate energy spectra, spectroscopic factors, beta decay properties, transition probabilities and the lifetime of the resonance state in 25Al within the framework of nuclear shell model. The theoretical results agree reasonably well with the experimental data. However, a detailed study for each set to identify the most preferred interaction for this nucleus is performed. Calculated lifetimes using two of the interactions (w, cw) agree better with the central value of the experimental lifetime of the resonance state measured in the present work.

High spin states of 40K populated through the 27Al(19F, alpha np) 40K reaction at 68 MeV beam energy were studied using the Indian National Gamma Array (INGA) facility. Six new levels and fourteen new transitions were added to the existing level scheme. The spins and parities of most of the levels were assigned, modified, or confirmed from RDCO, RADO, and linear polarization measurements. The multipole mixing ratios (8) for most of the transitions were measured. Large -basis shell -model calculations were performed to understand the microscopic origin of the levels. Different particle restrictions in sd and pf shell orbitals were used to explain the experimental results.

High-spin positive parity states of $^{50}\mathrm{V}$, populated through the $^{48}\mathrm{Ti}(^{4}\mathrm{He},np)^{50}\mathrm{V}$ reaction with a 48 MeV $\ensuremath{\alpha}$ beam, have been studied using the Indian National Gamma Array (INGA) facility. A few new levels and $\ensuremath{\gamma}$-ray transitions have been added to the level scheme utilizing the results of intensity, directional correlation, and linear polarization measurements. Lifetimes of a few excited states have been measured for the first time using the Doppler shift attenuation method (DSAM). Large basis shell model calculations have been performed within the $fp$ valence space to understand the microscopic origin of the excited states. Apart from the ground state yrast band [having a $\ensuremath{\pi}(1{f}_{7/2}^{3})\ensuremath{\bigotimes}\ensuremath{\nu}(1{f}_{7/2}^{7})$ particle configuration], a non-yrast band with a $\ensuremath{\pi}(1{f}_{7/2}^{3})\ensuremath{\bigotimes}\ensuremath{\nu}(1{f}_{7/2}^{6},2{p}_{3/2}^{1})$ particle configuration has also been identified. The interplay between single-particle and collective modes of excitation have been investigated in the observed bands by analyzing the particle partitions and spectroscopic quadrupole moments, both calculated using large basis shell model calculations.

High spin states of $^{40}\mathrm{K}$ populated through the $^{27}\mathrm{Al}(^{19}\mathrm{F},\ensuremath{\alpha}np)^{40}\mathrm{K}$ reaction at 68 MeV beam energy were studied using the Indian National Gamma Array (INGA) facility. Six new levels and fourteen new transitions were added to the existing level scheme. The spins and parities of most of the levels were assigned, modified, or confirmed from ${R}_{\mathrm{DCO}}$, ${R}_{\mathrm{ADO}}$, and linear polarization measurements. The multipole mixing ratios $(\ensuremath{\delta})$ for most of the transitions were measured. Large-basis shell-model calculations were performed to understand the microscopic origin of the levels. Different particle restrictions in $sd$ and $pf$ shell orbitals were used to explain the experimental results.

The quadrupole transition strength B ( E 2) deduced from the measured level lifetimes using the Doppler shift attenuation method with the help of the Indian National Gamma Array, decreases with increasing spin for the band of interest in 82 Kr. In addition, the ratio of the dynamic moment of inertia with the B ( E 2) value increases along the band. Large basis shell -model calculations have been performed to understand the microscopic origin of the band of interest. The experimental results are reproduced well by the numerical calculations within the framework of a semiclassical geometric model, which conclusively establish the antimagnetic rotation in the shape -phase transition point nucleus 82 Kr in the A approximate to 80 mass region. Present investigation represents the first conclusive evidence of an antimagnetic rotational band based on the valence protons and neutrons in the 1 g 9 / 2 orbitals in an atomic nucleus.

High -spin positive parity states of 50 V, populated through the 48 Ti( 4 He , np ) 50 V reaction with a 48 MeV alpha beam, have been studied using the Indian National Gamma Array (INGA) facility. A few new levels and gamma -ray transitions have been added to the level scheme utilizing the results of intensity, directional correlation, and linear polarization measurements. Lifetimes of a few excited states have been measured for the first time using the Doppler shift attenuation method (DSAM). Large basis shell model calculations have been performed within the f p valence space to understand the microscopic origin of the excited states. Apart from the ground state yrast band [having a pi (1 f 3 7 /2 ) (R) nu (1 f 77 /2 ) particle configuration], a non-yrast band with a pi (1 f 37 /2 ) (R) nu (1 f 6 7 /2 , 2 p 1 3 /2 ) particle configuration has also been identified. The interplay between single -particle and collective modes of excitation have been investigated in the observed bands by analyzing the particle partitions and spectroscopic quadrupole moments, both calculated using large basis shell model calculations.

ΔT = 0 electric dipole transitions in self conjugate nuclei, forbidden by isospin selection rules, are readily seen in nature. This implies that the states participating in these transitions may not be of pure isospin T . This work identifies some of these transitions in a few upper- sd shell self-conjugate nuclei and attempts to calculate the degree of isospin mixing in these nuclei by using the standard two-level mixing formalism in a semi-empirical approach. The physically observed E1 transitions are broken down into two theoretically allowed ΔT = 1 channels. These allowed components have been calculated within the shell model. Our results are consistent with both theoretical and experimental values found in the literature.

High-spin states of neutron-deficient trans-lead nucleus $$^{204}\hbox {At}$$ were populated up to $$\sim 8\,\mathrm{MeV}$$ excitation through the $$^{12}\hbox {C} + ^{197}\hbox {Au}$$ fusion evaporation reaction. Decay of the associated levels through prompt and delayed $$\gamma $$ -ray emissions were studied to evaluate the underlying nuclear structure. The level scheme, which was partly known, was extended further. An isomeric $$16^+$$ level with observed mean lifetime $$\tau =52 \pm 5\, \mathrm{ns}$$ , was established from our measurements. Attempts were made to interpret the excited states based on multi quasiparticle and hole structures involving $$2f_{5/2}$$ , $$1h_{9/2}$$ , and $$1i_{13/2}$$ shell model states, along with moderate core excitation. Magnetic dipole band structure over the spin parity range:  $$16^+$$ – $$23^+$$ was confirmed and evaluated in more detail, including the missing cross-over E2 transitions. Band-crossing along the shears band was observed and compared with the evidence of similar phenomena in the neighbouring $$^{202}\hbox {Bi}$$ , $$^{205}\hbox {Rn}$$ isotones and the $$^{203}\hbox {At}$$ isotope. Based on comparison of the measured B(M1)/B(E2) values for transitions along the band with the semiclassical model based estimates, the shears band of $$^{204}\hbox {At}$$ was established along with the level scheme.

Lifetimes of a few negative parity levels and multipole mixing ratios (delta) for a few dipole transitions in V-49, populated through the Ti-48(He-4, 2np)V-49 reaction with a 48 MeV He-4 beam, were measured. The Indian National Gamma Array (INGA) facility was used to detect gamma rays at three different angles. Large basis shell model calculations were performed to understand the microscopic origin of these levels and to interpret the observations. K mixing between different K bands in V-49 were established from one-nucleon-transfer spectroscopic factor calculations and total Routhian surface (TRS) calculations.

The excited states of odd-odd 154Ho nucleus have been studied by the 141Pr(16O, 3n)154Ho reaction at Elab= 82 MeV utilizing the Indian National Gamma Array (INGA) setup at BARC-TIFR Pelletron facility, Tata Institute of Fundamental Research, Mumbai. Data from γ−γ coincidence, directional correlation (DCO), and polarization measurements have been analyzed to assign and confirm the spins and parities of the levels. The reported level scheme of 154Ho has been improved by including new levels and transitions. Mixing ratios for the mixed transitions extracted from DCO ratios and parity assignments from polarisation data are reported for the first time. The low-lying states in H154o, which are mostly collective, characterized by regularity in the excitation spectra, are proposed to be arising from neutron excitation. At higher excitation, there is a transition from collective to single-particle character, accompanied by the appearance of irregular and complex structure caused by proton excitation. The newly identified E1 gamma transitions connecting the low-lying positive and negative parity bands indicate octupole correlation in 154Ho. These new connections also support the phenomenological analysis to interpret the observed experimental features from a different perspective.

The low-lying states of 117,118Sn have been studied from the decay of 117g,118mSb, and 117mSn. These long-lived species were populated through the reaction 4He + natIn at Elab = 32 MeV. Singles, as well as γ-γ coincidence data, were acquired. The uncertainties in the placement of some of the γ-rays in the excitation spectra of 118Sn observed by previous workers have been removed. A γ-ray (984 keV) previously assigned to 118Sn has been eliminated from the level scheme, based on the present analysis. The decay half-lives of 117g,118mSb have been remeasured. The slope method and deconvolution technique have been used to determine the half-lives of a few isomeric states in 117,118Sn. The results are interpreted in the framework of large scale shell model calculations performed in the 50 - 82 valence shell using truncations. Although the excitation energies were not reproduced well, the theoretical calculations could reasonably reproduce the isomers' transition probabilities due to their nearly pure configuration.

The [Formula: see text]C([Formula: see text]Ne, [Formula: see text]O)[Formula: see text]O reaction has been used for the first time to determine ANC of [Formula: see text]O levels. The [Formula: see text]C([Formula: see text]Ne, [Formula: see text]O)[Formula: see text]O [Formula: see text]-transfer angular distributions are measured at [Formula: see text][Formula: see text]MeV and used to determine the ANC of the ground, 6.05[Formula: see text]MeV ([Formula: see text]), 6.13[Formula: see text]MeV ([Formula: see text]), 6.92[Formula: see text]MeV ([Formula: see text]) and 7.12[Formula: see text]MeV ([Formula: see text]) states of [Formula: see text]O. The ANC values are [Formula: see text] [Formula: see text] [Formula: see text], [Formula: see text] [Formula: see text], [Formula: see text] [Formula: see text], [Formula: see text] [Formula: see text] and [Formula: see text] [Formula: see text]. Astrophysical S-factors at 300[Formula: see text]keV are extracted [Formula: see text]) keV b and [Formula: see text] keV b[Formula: see text] using these ANC values by R-matrix theory.

Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, India Mody University of Science and Technology, Sikar, Rajasthan 332311, India University of Calcutta, Kolkata 700009, India Saha Institute of Nuclear Physics, Bidhannagar, Kolkata 700064, India Department of Physics, Indian Institute of Technology (BHU), Varanasi 221005, India 6 Indian Institute of Technology, Kharagpur-721302, India 7 Inter University Accelerator Centre, New Delhi 110067, India *Email: abijitbisoi@gmail.com