arXiv subjects

Subhrajit Sahoo

Publications and source records attributed to Subhrajit Sahoo.

7 recordsLinked to original sources

arXiv2026

Ab initio study of $\beta$-decay and pairing in $N=Z$ nuclei

We investigate the $\beta$-decay properties of $rp$-process waiting-point nuclei $^{72}$Kr, $^{68}$Se, and $^{64}$Ge from realistic nuclear forces based on chiral effective field theory. The \textit{ab initio} valence-space in-medium similarity renormalization group method is employed for this purpose to consistently derive Hamiltonians and Gamow-Teller operators from chiral two- and three-nucleon interactions. The calculated half-lives and branching ratios indicate that nearly the entire decay intensity is confined within 1 MeV of excitation energy in the daughter nuclei. We address the isoscalar and isovector pairing and their impact on ground state properties of these waiting-point nuclei, along with several other $N=Z$ systems in the $fp$-shell. Our results do not provide evidence for an isoscalar condensate or any dominant isovector pairing condensate-like phase in these $N=Z$ nuclei. We present the full $B(\mathrm{GT})$ strength distributions and discuss the influence of pairing correlations on them. The present work provides a microscopic picture of $\beta$-decay strengths and pairing in $N=Z$ nuclei far from the stability line.

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arXiv2025

Ab initio study of island of inversion in odd-$A$ nuclei: Structure of $^{31,33}$Mg

We study the $N=20$ island of inversion region in the odd-$A$ Ne and Mg isotopes from the fundamental nuclear forces based on chiral two- and three-nucleon potentials. The state-of-the-art \textit{ab initio} valence space in medium similarity renormalization method was used for this purpose. Our study focuses on the evolution of single-particle states and discusses their transition into the island of inversion through particle-hole excitations across the $N=20$ shell gap. The computed low-lying states and magnetic moments are in good agreement with the experimental data. We presented the rotational band structures, established via $E2$ transitions, in $^{31}$Mg and $^{33}$Mg, which emerge from both normal and intruder configurations at low excitation energies. Our results suggest the presence of weak, moderate, and strongly prolate-deformed configurations at low energy in both isotopes. The present work offers valuable insights into the configurations and shapes of low-lying states in nuclei within the island of inversion, enhancing our understanding of the structures of exotic nuclei from first principles.

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arXiv2025

Intruder structures in $^{32}$Si and $^{29}$Al

We have studied $^{32}$Si and $^{29}$Al using $^{12}$C($^{22}$Ne,2p) and $^{12}$C($^{22}$Ne,$\alpha$p) fusion-evaporation reactions. In both cases, we observed significant population of high-spin structures distinct from the ground-state yrast bands. In $^{32}$Si, most of the high-energy states feed into a $J^{\pi} = 5^-$ nanosecond isomer. In $^{29}$Al, we identified a rotor-like negative-parity band with a $J^{\pi} = 7/2^-$ band-head. Doppler shift lifetime measurements were performed for all observed states. These results were compared to shell model calculations and interpreted in terms of proton and neutron cross-shell excitation.

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arXiv2024

Nuclear structure properties of $^{193-200}$Hg isotopes within large-scale shell model calculations

Large-scale shell-model calculations have been performed to study the nuclear structure properties of Hg isotopes with mass varying from $A=193$ to $A=200$. The shell-model calculations are carried out in the 50 $\leq Z \leq$ 82 and 82 $ \leq N \leq$ 126 model space using monopole-based truncation. We present detailed studies on low-energy excitation spectra, energy systematics, and collective properties of Hg isotopes, such as reduced transition probabilities, quadrupole, and magnetic moments along the isotopic chain. The evolution of wave function configurations with spin is analyzed in the case of even-$A$ Hg isotopes. The shell-model results are in reasonable agreement with the experimental data and predictions are made where experimental data are unavailable. The shapes of Hg isotopes are also investigated through the energy-surface plots.

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arXiv2024

Evolution of shell structure at $\mathbf{N=32}$ and 34: Insights from realistic nuclear forces

We investigated the evolution of shell structure at $N=32$ and 34 in neutron-rich nuclei beyond the stability line using realistic nuclear forces, employing the state-of-the-art valence-space in-medium similarity renormalization group method. The shell gaps are discussed from the excitation energies of the first $2^+$ states and the evolution of effective single-particle energies. We addressed different components of the nuclear interaction--central, spin-orbit, and tensor--and their roles in the development of shell gaps far from stability. The calculated results align well with the available experimental data and suggest a strengthening of the $N=34$ subshell gap and a weakening of the $N=32$ subshell gap below Ca. Additionally, the low-energy structures of the exotic $N=32$ isotones below Ca revealed that their ground states exhibit large deformation and coexist with a weakly deformed band at low excitation energy. The present work demonstrates essential components of the nuclear force in shaping magic numbers far from stability and provides deeper insights into the structure of exotic nuclei from the underlying nuclear forces.

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arXiv2024

Isoscalar, isovector and orbital contributions in $M1$ transitions from analogous $M1$ and Gamow-Teller transitions in $T=\frac{1}{2}$ mirror nuclei

The isoscalar and isovector components and their contributions to $M1$ transitions are discussed in the odd-$A$, $T=1/2$ mirror nuclei with mass number ranging from $A=23$ to 37. The orbital contributions in various $M1$ transitions and ground state magnetic moments are calculated by comparing analogous $M1$ and Gamow-Teller transitions between mirror pairs. The orbital contributions in different $M1$ transitions are explained on the basis of configurations of the initial and final states involved. In magnetic moments, the orbital contributions are found to be dependent on the deformation and single-particle nature of the states. All the $T=1/2$ mirror pairs are studied using isospin non-conserving interaction. The results are also compared with predictions from \textit{ab initio} effective interaction derived from realistic nuclear forces.

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arXiv2022

Study of structure and radii for $^{20-31}$Na isotopes using microscopic interactions

In this work, Na isotopes with mass varying from $A=$ 20 to 31 have been studied using DJ16A, JISP16 and N3LO microscopic effective interactions in the $sd$-shell. These effective interactions are derived for $sd$-shell using no-core shell model wavefunctions and a unitary transformation method. We have also performed calculation with IMSRG effective interactions targeted for a particular nucleus. The studies include a detailed analysis of ground state binding energy, low-lying spectra, and electromagnetic properties such as reduced electric quadrupole transition strengths, quadrupole and magnetic dipole moments of the Na chain. The results obtained from these microscopic effective interactions were compared with the experimental data as well as with the results of phenomenological interaction USDB. The charge radii of Na isotopes are evaluated using shell model harmonic oscillator wave functions. In addition to charge radii, matter radii and neutron skin thickness in the Na chain are discussed with a focus on neutron-deficient Na isotopes.

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