Projected Shell Model Research Articles

Coexistence of low-K oblate and high-K prolate g9/2 proton-hole bands in 115Sb

A positive parity sequence of ΔI=2γ 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.

First-forbidden transition of nuclear β decay by projected shell model

The first-forbidden transition of nuclear β decay is expected to play crucial roles in many aspects in nuclear physics, nuclear astrophysics and particle physics such as the stellar β-decay rates and the reactor anti-neutrino spectra. In this work we develop the projected shell model (PSM) for description of first-forbidden transition of nuclear β decay for the first time. Detailed theoretical framework and logics are provided, and 35 dominant first-forbidden transitions that are expected to be important for the reactor anti-neutrino spectra problems are calculated and compared systematically with the data to test the new development of the PSM. The corresponding experimental Logf0t values are described reasonably, and the quenching factors of nuclear matrix elements are found to affect the Logf0t values as well as the related shape factors, which may be helpful for better understanding of the reactor anti-neutrino spectra problems.

Level structures of 96Tc and their microscopic description

High spin states in the 96Tc nucleus were populated in the 75As(28Si, 4p3n) fusion-evaporation reaction at E lab = 120 MeV and the de-excitations were investigated through in-beam γ-ray spectroscopic techniques using indian national gamma array spectrometer consisting of 18 clover Ge detectors. The present level scheme of the 96Tc nucleus has been extended substantially with the addition of about forty five new γ transitions. The level structures in 96Tc have been established up to excitation energy ∼10 MeV and angular momentum ∼25ℏ. Level structures of 96Tc nucleus are discussed in the framework of triaxial projected shell model calculations.

Systematic Study of Even–Even Hafnium Isotopes by Using Projected Shell Model

Systematic Study of Even–Even Hafnium Isotopes by Using Projected Shell Model

Excited nuclear states and K-isomers in the projected shell model

Excited nuclear states and K-isomers in the projected shell model

Recent progress in configuration–interaction shell model

Since Mayer and Jensen employed the single-particle shell model to interpret the magic numbers, various microscopic nuclear models have been developed to study the nuclear force and structure. The configuration–interaction shell model (CISM), performed in truncated model space with the inclusion of the residual interaction, is one widely-used nuclear structure model. In the last decade, CISM has progressed in investigating the cross-shell excitation in exotic light nuclei, the similarity and difference in mirror nuclei, and the isomerism and seniority conservation in medium and heavy nuclei. Additionally, researchers have attempted to construct effective Hamiltonians for nuclei near [Formula: see text]Sn and [Formula: see text]Pb through a unified way in the CISM framework. In parallel, related models, including the nucleon-pair approximation (NPA) approach, the Monte Carlo shell model (MCSM), the projected shell model (PSM), the Gamow shell model (GSM), etc., have also been extensively developed and validated in the last decade. This paper reviews the recent progress in CISM and some related models.

Stellar weak-interaction rates for rp-process waiting-point nuclei from projected shell model

We propose a projected shell model (PSM) for description of stellar weak-interaction rates between even-even and odd-odd nuclei with extended configuration space where up to six-quasiparticle (qp) configurations are included, and the stellar weak-interaction rates for eight rp-process waiting-point (WP) nuclei, 64Ge, 68Se, 72Kr, 76Sr, 80Zr, 84Mo, 88Ru and 92Pd, are calculated and analyzed for the first time within the model. Higher-order qp configurations are found to affect the underlying Gamow-Teller strength distributions and the corresponding stellar weak-interaction rates. Under rp-process environments with high temperatures and densities, on one hand, thermal population of excited states of parent nuclei tends to decrease the stellar β+ decay rates. On the other hand, the possibility of electron capture (EC) tends to provide increasing contribution to the rates with temperature and density. The effective half-lives of WP nuclei under the rp-process peak condition are predicted to be reduced as compared with the terrestrial case, especially for 64Ge and 68Se.

Triaxial projected shell model approach for negative parity states in even-even nuclei

Triaxial projected shell model approach for negative parity states in even-even nuclei

Projected shell model description of nuclear level density: Collective, pair-breaking, and multiquasiparticle regimes in even-even nuclei

Projected shell model description of nuclear level density: Collective, pair-breaking, and multiquasiparticle regimes in even-even nuclei

Microscopic study of normal deformed bands in 167,169,171Lu

The normal deformed bands of [Formula: see text]Lu isotopes have been studied by using projected shell model approach. The band head spins, configurations and energies of all the normal deformed bands are reproduced well by the above said approach. The present calculations have predicted [Formula: see text] band head spin for [523]7/2− bands of [Formula: see text]Lu. The observed systematics of aligned angular momenta and the experimental differences in frequencies around the backbends for all the normal deformed bands are reproduced well by the theoretical results. Besides this, the observed backbends or upbends in these isotopes may be ascribed to the alignment of a pair of neutrons in the neutron [Formula: see text] orbital. Although the theoretical [Formula: see text] values obtained from the projected shell model wavefunctions overestimate the experimental [Formula: see text] values in [Formula: see text]Lu, yet they are close to the measured values, considering the precision of measurement. The reduction in the theoretical [Formula: see text] values around the band crossing region may be ascribed to change in nuclear structure of yrast bands due to neutron pair alignment in [Formula: see text] orbital.

Three-quasineutron γ-band in 127Xe

Structures of negative parity multi-quasiparticle states in 127Xe have been investigated through in-beam γ-ray spectroscopy. Excited states were populated via the 122Sn(9Be, 4nγ)127Xe fusion-evaporation reaction at E beam = 48 MeV. Two new negative parity bands have been identified and their structures have been discussed using the triaxial projected shell model (TPSM) approach. One of the bands is established above the I π = 27/2− state at 3702 keV and based on the experimental inferences and TPSM results, this band is interpreted as a γ-band built on a three-quasineutron configuration. The second sequence, found above I π = 31/2− state at 4848 keV, is proposed to have a two-proton aligned configuration (), considering the properties of this band with the neighbouring isotopes. The analysis of the TPSM wave function substantiates the proposed interpretation of this band.

Revisiting band structures in 118Xe nucleus via in-beam γ-ray spectroscopy* *The authors are grateful for the pelletron and support staff of IUAC, New Delhi. We would also like to acknowledge the contribution of the INGA collaboration, which is partially funded by the Department of Science and Technology (DST, GoI; project no. IR/S2/PF-03/2003-I) and University Grants Commission (UGC). This work was

The neutron deficient Xe nuclei with A 120 are predicted to have strong octupole correlation at low spins. In the present study, an attempt was made to improve upon the level scheme and also to examine the signatures of octupole correlation in Xe via high spin γ-ray spectroscopy. High spin states in Xe have been populated via the Nb(Si, p2n)Xe fusion-evaporation reaction at a beam energy of 115 MeV provided by the 15 UD pelletron accelerator facility at IUAC, New Delhi. In the experiment, seven new γ-transitions have been found and placed appropriately in the level scheme. A theoretical study using the triaxial projected shell model (TPSM) approach suggests that the first bandcrossing is due to the alignment of two neutrons, and a parallel band tracking the yrast configuration is the γ-band built on the two-quasiparticle state. Enhanced E1 transition rates measured between opposite parity bands involving νh and ν d orbitals having Δj = Δl = 3 indicate the presence of octupole correlation in this nucleus.

Evidence of transverse wobbling motion in Eu151

Transverse wobbling was investigated in the Eu151 nucleus by populating the excited states using Nd148(Li7, 4n)Eu151 at a beam energy of 30 MeV. Three new interconnecting transitions have been placed between the two negative parity bands. The M1/E2 character of the interconnecting ΔI=1 transitions between the negative parity bands was extracted from the mixing ratios using the RDCO and linear polarization method. The spin and parity of the states of different bands have also been assigned. The dominant E2 character of the interlinking transitions between the yrast and first phonon wobbling band and the dominant M1 character between the yrast band and its signature partner band indicate the presence of transverse wobbling in the Eu151 nucleus. It is further demonstrated that the triaxial projected shell model approach describes the observed experimental properties.7 MoreReceived 21 December 2022Revised 22 January 2023Accepted 8 May 2023DOI:https://doi.org/10.1103/PhysRevC.107.054310©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsNuclear structure & decaysProperties150 ≤ A ≤ 189TechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Wobbling Motion in Nuclei

Wobbling motion as an exotic collective mode in nuclei without axial symmetry, was intensively discussed during the last few years. The observation of the newly proposed transverse wobbling, first reported in 135Pr and soon after in nuclei from other mass regions, was considered as a significant discovery in low-spin nuclear structure. However, both the reported experimental results and the proposed theoretical models were actively questioned in work devoted to the study of the low-spin wobbling mode in the same nuclei. We recently re-measured the electromagnetic character of the ΔI=1 transitions connecting the one- to zero-phonon and the two- to one-phonon wobbling bands in 135Pr, showing their predominant M1 magnetic character, which is in contradiction with the wobbling interpretation. These new experimental results, which were reproduced by either the quasiparticle-plus-triaxial-rotor model and interacting boson-fermion model calculations, are against the previously proposed wobbling nature of the low-spin bands in 135Pr. On the other hand, we obtained conclusive experimental evidence for the theoretically proposed transverse wobbling bands at medium spin in 136Nd. The comparison of the experimental data with calculations using the triaxial projected shell model as well as a new particle-rotor model with frozen orthogonal geometry of the active nucleons, supports the description in terms of transverse wobbling of medium-spin bands in triaxial even-even nuclei.

Description of energy spectrum and signature inversion for $${}^{160}\hbox {Tm}$$ and $${}^{161}\hbox {Tm}$$ isotopes using the projected shell model

Description of energy spectrum and signature inversion for $${}^{160}\hbox {Tm}$$ and $${}^{161}\hbox {Tm}$$ isotopes using the projected shell model

Microscopic aspects of γ softness in atomic nuclei

One of the main research themes in quantum many-body systems is the emergence of collective features from microscopic degrees of freedom. Using the microscopic approach of the triaxial projected shell model, the authors demonstrate that admixing a few quasiparticle excitations into the vacuum configuration with a fixed triaxiality parameter $\ensuremath{\gamma}$ provides a quantitative description of the shape fluctuations of the $\ensuremath{\gamma}$-soft nucleus ${}^{104}$Ru. The collective features are elucidated using the quadrupole shape invariant analysis, and also the staggering phase classification of the $\ensuremath{\gamma}$ band.

Stellar β− Decay Rates for 63Co and 63Ni by the Projected Shell Model

β− decay for 63Co-63Ni-63Cu region nuclei play important roles in core-collapse supernovae and the slow neutron-capture (s) process. In this work, the stellar β− decay rates for 63Co and 63Ni are studied within the projected shell model where the effects of thermally populated parent-nucleus excited states are analyzed. For 63Co, the calculated stellar β− decay rates are lower than the results of the conventional shell model. For the s-process branching point 63Ni, the β− decay rate under a terrestrial condition is well described, and the calculated stellar β− decay rates in the s-process condition turn out to increase with stellar temperature due to the contribution from parent-nucleus excited states.

Structural evolution and shape transitions of even-even neutron rich $$^{140-150}$$Ba nuclei using triaxial projected shell model

Structural evolution and shape transitions of even-even neutron rich $$^{140-150}$$Ba nuclei using triaxial projected shell model

Investigation of the high-spin yrast band structure of Pu236–246 isotopes

The available data on some actinide nuclei point to certain significant features of the rotational yrast band and other excited bands. The rotational properties of plutonium isotopes ($^{236--346}\mathrm{Pu}$) were studied via projected shell model (PSM). Calculations are based on the Hamiltonian of the PSM which includes the formed part of a single particle, the $Q\ensuremath{-}Q$ force, and the residual interaction of monopole and quadrupole pairings. The results of the calculated energy levels of the yrast band are then compared with available experimental data and a good agreement has been found. The crossing between two-quasiparticle (2qp) excited bands and the ground state band (g band) in the high-spin regions has been analyzed in terms of band diagrams. The upbendings observed in the kinematic moments of inertia (${j}^{(1)}$ MOI) curves for $^{236--346}\mathrm{Pu}$ isotopes are due to the effect of two aligning nucleons that occupy excited bands and the $\ensuremath{\nu}({j}_{15/2}$), $\ensuremath{\pi}({i}_{13/2}$) high-$j$ intruder orbits. The PSM successfully reproduces the observed upbending in ${j}^{(1)}$ as well as the upturning and downturning in ${j}^{(2)}$. For the $^{240}\mathrm{Pu}$ isotope, the PSM predicts a simultaneous alignment of neutrons ${\ensuremath{\nu}}^{2} [1/2,\ensuremath{-}7/2] {K}^{\ensuremath{\pi}}$ = ${4}^{+}$ and protons ${\ensuremath{\pi}}^{2} [\ensuremath{-}3/2,5/2] {K}^{\ensuremath{\pi}}$ = ${1}^{+}$ bands cross the g band at spin $I=22$. We expect it to be mainly responsible for the disagreement at $I=22$. Furthermore, electric quadrupole transition probabilities $B(E2)$ and the gyromagnetic factor ($g$ factor) for the yrast band energy levels are also studied.

Study of high spin phenomena in even-even dysprosium isotopes by using projected shell model

Study of high spin phenomena in even-even dysprosium isotopes by using projected shell model