arXiv subjects

S. P. Rouoof

Publications and source records attributed to S. P. Rouoof.

7 recordsLinked to original sources

arXiv2026

Microscopic investigation of $E2$ matrix elements in atomic nuclei -- II

The present work is a continuation of our earlier investigation with the primary objective to systematically calculate the $E2$ matrix elements using the microscopic approach of the triaxial projected shell model (TPSM). In the earlier work, we studied nine nuclides of $^{72}$Ge, $^{76}$Ge, $^{104}$Ru, $^{168}$Er, $^{186}$Os, $^{188}$Os, $^{190}$Os, $^{192}$Os, and $^{194}$Pt. In the present work six more nuclides of $^{70}$Ge, $^{76,78,80,82}$Se, and $^{100}$Mo have been investigated. The Coulomb excitation data has recently become available for $^{70}$Ge and other nuclides were inadvertently omitted in our earlier investigation. It is demonstrated that TPSM approach provides a good description of the available experimental data and most of the nuclides, except for $^{76}$Se and $^{100}$Mo, are shown to have $γ$ soft behaviour. Further, it is demonstrated that in contrast to the predictions of the phenomenological collective model, TPSM calculations depict no clear correlation between the energy staggering pattern of the $γ$ band and the deduced shape invariant quantities using the Kumar-Cline sum rules.

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arXiv2026

Microscopic investigation of $γ~$ vibrational band structures in odd-mass nuclei

A systematic investigation of the high-spin band structures observed in $^{103,105,107,109}$Nb and $^{103,105,107,109}$Tc nuclides is performed using the triaxial projected shell model (TPSM) approach. For $^{103,105}$Nb isotopes, four bands have been populated with the lowest three bands corresponding to yrast, $γ$ and 2$γ$ bands. The nature of the fourth observed band has remained unresolved as it has been shown from the transition intensity ratios that this band cannot correspond to the expected 3$γ$ band. It is demonstrated in the present work that this fourth band is the second $γ$ band, resulting from the combination, $K=K_0-2$ with $K_0$ being the "$K$" value of the parent configuration. The excitation energy and other properties of this band structure are predicted for all the studied nuclides.

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arXiv2025

Microscopic investigation of $E2$ matrix elements in atomic nuclei

A systematic analysis of $E2$ matrix elements of $^{72}$Ge, $^{76}$Ge, $^{168}$Er, $^{186}$Os, $^{188}$Os, $^{190}$Os, $^{192}$Os and $^{194}$Pt nuclides is performed using the beyond mean-field approach of triaxial projected shell model (TPSM). For these nuclei, large sets of $E2$ matrix elements have been deduced from the multi-step Coulomb excitation experiments, and it is shown that TPSM approach provides a reasonable description of the measured transitions. We have evaluated 1496 $E2$ matrix elements up to spin, $I=10$ for the eight nuclei studied, and tabulate them for future experimental and theoretical comparisons. Further, shape invariant analysis has been performed with the calculated $E2$ transitions using the Kumar-Cline sum rules. It is inferred from the analysis that the resulting shape, after configuration mixing of the quasiparticle states, transforms from $γ$-rigid to that of $γ$-soft for some nuclei, in conformity with the experimental data.

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arXiv2024

Isospin symmetry breaking in atomic nuclei

The importance of the isospin symmetry and its breaking in elucidating the properties of atomic nuclei is reviewed. The quark mass splitting and the electromagnetic origin of the isospin symmetry breaking (ISB) for nuclear many-body problem is discussed. The experimental data on isobaric analogue states cannot be described only with the Coulomb interaction, and ISB terms in the nucleon-nucleon interaction are needed to discern the observed properties. In the present work, the ISB terms are explicitly considered in nuclear energy density functional and spherical shell model approaches, and a detailed investigation of the analogue states and other properties of nuclei is performed. It is observed that isospin mixing is largest for the $N=Z$ system in the density functional approach.

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arXiv2024

Fingerprints of the triaxial deformation from energies and $B(E2)$ transition probabilities of $γ$-bands in transitional and deformed nuclei

The energies and $B(E2)$ transitions involving the states of the ground- and $γ$-bands in thirty transitional and deformed nuclei are calculated using the triaxial projected shell model (TPSM) approach. Systematic good agreement with the existing data substantiates the reliability of the model predictions. The Gamma-rotor version of the collective Bohr Hamiltonian is discussed in order to quantify the classification with respect to the triaxial shape degree of freedom. The pertaining criteria are applied to the TPSM results and the staggering of the energies of the $γ$-bands is analyzed in detail. An analog staggering of the intra-$γ$ $B(E2,I\rightarrow I-2)$ is introduced for the first time. The emergence of the staggering phenomena in the transitions is explained in the terms of interactions between the bands.

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arXiv2023

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

The triaxial projected shell model (TPSM) approach is generalized to investigate the negative parity band structures in even-even systems. In the earlier version of the TPSM approach, the quasiparticle excitations were restricted to one major oscillator shell and it was possible to study only positive parity states in even-even systems. In the present extension, the excited quasiparticles are allowed to occupy two major oscillator shells, which makes it possible to generate the negative parity states. As a major application of this development, the extended approach is applied to elucidate the negative parity high-spin band structures in $^{102-112}$Ru and it is shown that energies obtained with neutron excitation are slightly lower than the energies calculated with proton excitation. However, the calculated aligned angular momentum ($i_x$) clearly separates the two spectra with neutron $i_x$ in reasonable agreement with the empirically evaluated $i_x$ from the experimental data, whereas proton $i_x$ shows large deviations. Furthermore, we have also deduced the transition quadrupole moments from the TPSM wavefunctions along the negative-parity yrast- and yrare- bands and it is shown that these quantities exhibit rapid changes in the bandcrossing region.

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arXiv2022

Microscopic aspects of $γ$-softness in atomic nuclei

The microscopic origin of the $γ$-softness (fluctuations in the triaxiality parameter $γ$ of the nuclear shape) observed in atomic nuclei is studied in the framework of the triaxial projected shell model approach, which is based on the deformed mean-field picture with multi-quasiparticle configuration space. It is demonstrated that the coupling to quasiparticle excitations drives the system from a $γ$-rigid to a $γ$-soft pattern. As an illustrative example for a $γ$-soft nucleus, a detailed study has been performed for the $^{104}$Ru nucleus. The experimental energies and a large sample of measured $E2$ matrix elements available for this nucleus are reproduced quite accurately. The shape invariant analysis of the calculated $E2$ matrix elements elucidates the $γ$-soft nature of $^{104}$Ru.

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