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In neutron-rich nuclei neighboring 42Si, the quenching of the N = 28 shell gap occurs and is expected to induce shape coexistence in their excitation spectra. We have applied the theoretical framework of antisymmetrized molecular dynamics with the Gogny D1S density functional to describe the shape coexistence in the N = 28 isotones 40Mg, 42Si, and 44S. We show that different nuclear shapes coexist in these nuclei: Rigid shapes with different deformations coexist in 40Mg and 42Si, while 44S exhibits large-amplitude collective motion and does not have any particular shape. These characteristics are reflected well in the monopole transition strengths that can be utilized as a probe for the shape coexistence. [ABSTRACT FROM AUTHOR]

The cross-sections of (d,p), (d,n) and (d,t) transfer reactions are analyzed depending on different density distributions, temperature cases, nuclear potentials and nucleon-nucleon interactions. The calculations are based on the DWBA method. The theoretical results and experimental data are compared, and the analyzes are made about the similarities and differences of the results. Additionally, new potential parameter sets for each transfer reaction are developed. Finally, alternative density, nuclear potential and nucleon-nucleon interactions are proposed for the analysis of (d,p), (d,n) and (d,t) transfer reactions. [ABSTRACT FROM AUTHOR]

The work reports a novel application of the interacting boson model in light-mass region around 48Ca, that takes into account intruder states and configuration mixing. The model is shown to provide a reasonable description of the observed low-lying yrast and yrare states of the N = 28 even–even isotones from Si to Fe, and even–even Ca isotopes. The nature of 0 2 + states is addressed in terms of the competition between spherical and deformed intruder configurations, and the rigidity of the N = 28 shell gap is tested, particularly for 44S. The 0 2 + isomer in 44S is shown to arise from a weak mixing between the two configurations and called as shape isomer. The unresolved low-lying spectra in 46Ar is also approached using the core-excitations across N = 28 shell. The SU(3) structure in 42Si is supported by the present calculation. The nearly spherical nature of 50Ti, 52Cr, 54Fe and 42,44,46Ca isotopes is found, while the core excitations are found to be essential for the description of yrare states. Shell model calculation is also performed for comparison. [ABSTRACT FROM AUTHOR]

We performed ab initio valence-space in-medium similarity renormalization group calculations based on chiral nucleon-nucleon and three-nucleon interactions to study the neutron-rich nuclei around N = 28 , where the experimental and theoretical evidence point to a rapid transition from spherical to rotational regimes. First, the rotational spectra of 40Mg, 42Si, and 44S are established theoretically, anchored by the calculated E 2 transition strength. The results suggest that 40Mg and 42Si exhibit large deformations. After that, the erosion of the N = 28 shell closure, especially the evolutions of shape deformation and the emergence of shape coexistence, are discussed in N = 28 even-even isotones ranging from 40Mg to 48Ca. Finally, the shell evolution of N = 28 in Mg and Si chains is discussed based on the experimental and predicted excitation energies of low-lying states. The results from our ab initio calculations align well with available experimental data, furnishing essential insights into the structure of neutron-rich nuclei, particularly deformations in the vicinity of 40Mg and 42Si. [ABSTRACT FROM AUTHOR]

We performed ab initio valence-space in-medium similarity renormalization group calculations based on chiral nucleon-nucleon and three-nucleon interactions to study the neutron-rich nuclei around N=28, where the experimental and theoretical evidence point to a rapid transition from spherical to rotational regimes. First, the rotational spectra of 40Mg, 42Si, and 44S are established theoretically, anchored by the calculated E2 transition strength. The results suggest that 40Mg and 42Si exhibit large deformations. After that, the erosion of the N=28 shell closure, especially the evolutions of shape deformation and the emergence of shape coexistence, are discussed in N=28 even-even isotones ranging from 40Mg to 48Ca. Finally, the shell evolution of N=28 in Mg and Si chains is discussed based on the experimental and predicted excitation energies of low-lying states. The results from our ab initio calculations align well with available experimental data, furnishing essential insights into the structure of neutron-rich nuclei, particularly deformations in the vicinity of 40Mg and 42Si.

The structure properties of nuclei that reside significantly away from the line of β -stability are currently the focus of both theoretical and experimental studies. Various theoretical methodologies are being employed to explore these nuclear structure properties. In our research, we have calculated several structure properties, including binding energy, charge radii, root mean square (rms) radii and their isotopic variations, two-neutron separation energy, shell gap, chemical potential, quadrupole deformation, density distribution, and single-particle energy for thorium nuclei, which are found both on and off the line of β -stability. Thorium nuclei are particularly intriguing due to their diverse practical applications, including their role in thorium-based nuclear reactors and their involvement at various stages of nucleosynthesis. This study helps us gain insight into how nuclear properties change with the number of neutrons and enables us to predict shell closures and nuclear stability. The estimated values were compared with available experimental and theoretical data and are found to be in good agreement. The departure from a linear trend observed around specific neutron numbers, specifically N = 126, 138, and 184, in graphs depicting various properties against neutron number and single-particle energy gap, can be attributed to the concept of neutron magic numbers. Among these, N = 126 and N = 184 are considered neutron magic numbers, while N = 138 is regarded as a semi-magic number. [ABSTRACT FROM AUTHOR]

The excited states of odd–odd 54 Mn ( Z = 25 , N = 29 ) nucleus have been investigated using the fusion evaporation reaction 55 Mn(α , α n) 54 Mn at the beam energy of 34 MeV. A new and improved level scheme of 54 Mn has been proposed in this work with the placement of 22 new γ -ray transitions. Spin and parity (J π ) of most of the levels in the revised level scheme have been firmly assigned. The placement of some of the already known γ rays in the level scheme and J π assignments of some of the levels reported earlier have also been revised. The new level scheme, which has been extended up to ∼ 6 MeV, provides new insight and interesting structural aspects of the generation of high angular momentum in this odd–odd Mn isotope with neutron number ( N = 29 ) just above the N = 28 shell gap. Three octupole-phonon-coupled negative parity states have been identified for the first time in this nucleus. E3 transitions have also been observed to decay from these states. Shell model calculations with two different interactions i.e. kb3gpn and gx1pn have been performed which well reproduced the low-lying, few-particle states but fail to reproduce the higher-lying multi-particle states. These higher-lying states have been understood as resulting from collective excitations. An oblate minimum obtained from the Total Routhian Surface calculations provides support to this conjecture. [ABSTRACT FROM AUTHOR]

The last decade has seen a rapid growth in our understanding of the microscopic origins of shape coexistence, assisted by the new data provided by the modern radioactive ion beam facilities built worldwide. Islands of the nuclear chart in which shape coexistence can occur have been identified, and the different microscopic particle–hole excitation mechanisms leading to neutron-induced or proton-induced shape coexistence have been clarified. The relation of shape coexistence to the islands of inversion, appearing in light nuclei, to the new spin-aligned phase appearing in N = Z nuclei, as well as to shape/phase transitions occurring in medium mass and heavy nuclei, has been understood. In the present review, these developments are considered within the shell-model and mean-field approaches, as well as by symmetry methods. In addition, based on systematics of data, as well as on symmetry considerations, quantitative rules are developed, predicting regions in which shape coexistence can appear, as a possible guide for further experimental efforts that can help in improving our understanding of the details of the nucleon–nucleon interaction, as well as of its modifications occurring far from stability. [ABSTRACT FROM AUTHOR]

The halo phenomenon in exotic nuclei has long been an important frontier in nuclear physics research since its discovery in 1985. In parallel with the experimental progress in exploring halo nuclei, the covariant density functional theory has become one of the most successful tools for the microscopic study of halo nuclei. Based on spherical symmetry, the relativistic continuum Hartree–Bogoliubov theory describes the first halo nucleus 11 Li self-consistently and predicts the giant halo phenomenon. Based on axial symmetry, the deformed relativistic Hartree–Bogoliubov theory in continuum has predicted axially deformed halo nuclei 42 , 44 Mg and the shape decoupling effects therein. Based on triaxial symmetry, recently the triaxial relativistic Hartree–Bogoliubov theory in continuum has been developed and applied to explore halos in triaxially deformed nuclei. The theoretical frameworks of these models are presented, with the efficacy of exploiting symmetries highlighted. Selected applications to spherical, axially deformed, and triaxially deformed halo nuclei are introduced. [ABSTRACT FROM AUTHOR]

Following the work of Giulio Racah and others from the 1940s onward, the rotational symmetry of atoms and ions, e.g., the conservation of angular momentum, has been utilized in order to efficiently predict atomic behavior, from their level structure to the interaction with external fields, and up to the angular distribution and polarization of either emitted or scattered photons and electrons, while this rotational symmetry becomes apparent first of all in the block-diagonal structure of the Hamiltonian matrix, it also suggests a straight and consequent use of symmetry-adapted interaction amplitudes in expressing the observables of most atomic properties and processes. We here emphasize and discuss how atomic structure theory benefits from exploiting this symmetry, especially if open-shell atoms and ions in different charge states need to be combined with electrons in the continuum. By making use of symmetry-adapted amplitudes, a large number of excitation, ionization, recombination or even cascade processes can be formulated rather independently of the atomic shell structure and in a language close to the formal theory. The consequent use of these amplitudes in existing codes such as Grasp will therefore qualify them to deal with the recently emerging demands for developing general-purpose tools for atomic computations. [ABSTRACT FROM AUTHOR]

The relativistic point-coupling model combined with complex momentum representation method (RMFPC-CMR method) is used to investigate the exotic phenomena in the neutron-rich Si, S, Ar, Ti, Cr, and Fe isotopes. The calculated two-neutron separation energies are compared with the relativistic Hartree–Bogoliubov calculations as well as the available experimental data. It is found that the new magic number N = 34 appears in Si and S isotopes and the traditional magic numbers N = 28 (in Si isotopes) and 50 (in Si, S, Ar, and Ti isotopes) disappear. In addition, the calculated single-particle energies and occupation probabilities of the bound and resonant states support the results and indicate that a neutron halo may occur on the neutron-rich side of Ti, Cr, and Fe isotopes. We also calculate the density distributions of neutrons and protons, and the ratios of the densities of the single-particle levels to the total neutron density. The results show that 76 - 80 Ti ( N = 54 - 58 ), 76 - 82 Cr ( N = 52 - 58 ), and 80 - 84 Fe ( N = 54 - 58 ) isotopes are possible halo nuclei, while Si, S, and Ar isotopes prefer to neutron skin. The prediction on the structure of halo and skin in the neutron-rich Si, S, Ar, Ti, Cr, and Fe isotopes are of referential value for experiment. [ABSTRACT FROM AUTHOR]

In recent years, shell model studies have significantly contributed in improving the nuclear input, required in simulations of the dynamics of astrophysical objects and their associated nucleosynthesis. This review highlights a few examples such as electron capture rates and neutrino-nucleus cross sections, important for the evolution and nucleosynthesis of supernovae. For simulations of rapid neutron-capture (r-process) nucleosynthesis, shell model studies have contributed to an improved understanding of half lives of neutron-rich nuclei with magic neutron numbers and of the nuclear level densities and γ -strength functions that are both relevant for neutron capture rates. [ABSTRACT FROM AUTHOR]

Fully self-consistent study of the charge radii in the long chains of isotopes from Ar to Ti is presented. The neutron-deficient and neutron-rich nuclei with pairing in both neutron and proton sectors, as well as the (semi-) magic nuclei around the closed neutron shells at , 28, 32 are treated within the Energy Density Functional (EDF) approach with the Fayans functional DF3-a. The performance of the DF3-a and its recent option Fy( , HFB) is analyzed in describing the absolute and differential rms radii. The scale of odd–even staggering is compared with one found in the CERN-CRIS experiments for Ca, K isotopes. The DF3-a calculations are consistent with magic behavior of charge radii in K isotopes at . A non-regular -dependent contribution due to the quasiparticle–phonon coupling is responsible for the universal increase of the charge radii after crossing the neutron shell at . Possible effects of deformation and higher power density gradient terms in the surface and pairing parts of the functional are mentioned. [ABSTRACT FROM AUTHOR]

The systematic search of axial ground state and the emergence of new gaps in neutron-rich 4 4 − 5 2 Ar isotopes are the challenging of current calculations of relativistic and nonrelativistic mean field models. For this purpose, we have employed the model based on Relativistic Hartree–Bogoliubov (RHB) with the density-dependent effective interaction of point coupling DD-PCX type. However, the nonrelativistic mean field calculations based on Hartree-Fock model were carried out with Skyrme SV-min parametrization. All the present calculations were performed within axial symmetries. The results provide that most of isotopes show an oblate-deformed ground state. In particular, 5 0 Ar and 5 2 Ar display a spherical shape in their ground states with SV-Min calculations. There is a notable signature of the sub-shell closure at neutron number N = 3 2 , whereas N = 3 4 is expected to be nearly quenched in the spherical ground. Furthermore, coexistence features are predicted in the neutron-rich 4 4 Ar isotope. We have also studied the neutron axial densities and its central depletion in the well-deformed grounds for the first time. In addition to these, the proton single-particle evolution and bubble-like structure at 4 6 Ar are very well reproduced with DD-PCX calculations. [ABSTRACT FROM AUTHOR]

In this paper, the validity of the shell-evolution picture is investigated on the basis of shell-model calculations for the atomic mass number 25 ≲ A ≲ 55 neutron-rich nuclei. For this purpose, the so-called SDPF-MU interaction is used. Its central, two-body spin–orbit, and tensor forces are taken from a simple Gaussian force, the M3Y (Michigan 3-range Yukawa) interaction, and a π + ρ meson exchange force, respectively. Carrying out almost a complete survey of the predicted effective single-particle energies, it is confirmed here that the present scheme is quite effective for describing shell evolution in exotic nuclei. [ABSTRACT FROM AUTHOR]

Inspired by the recent experimental evidences for double magicity in 52,54Ca, we have employed relativistic mean-field (RMF) approach with density-dependent meson-nucleon couplings using DD-ME2 parameter for a systematic study of nuclei with neutron numbers N = 32 and 34 with the help of ground state properties of even–even nuclei. Our extensive calculations include deformation, binding energies, 2p-separation energies, radii, etc. We compare our results with the available experimental data and another parameter of RMF. Our results of potential energy surface, two proton shell gap, isotopic shift, and normalized radius demonstrate signature of double magicity in N = 32 and 34 isotones, in particular for 46,48Si, 60,62Ni along with what found for 52,54Ca. [ABSTRACT FROM AUTHOR]