Narrow Results

In this paper, we have analyzed the ground state structural properties of fermium-isotopes in the mass range $221\le A\le 279$ within the relativistic mean-field with NL3${}^{\ast }$ and Relativistic Hartree–Bogoliubov approach with DD-ME2 parameter sets. The bulk properties, such as binding energy, root mean-square charge radius, quadruple deformation parameter, chemical potentials, two-neutron separation energy and differential two- neutron separation energy, are estimated for the above Fm- isotopic chain. All the calculated observables are compared with finite range droplet model (FRDM) predictions and experimental data wherever available. The analysis predicts the existence of shell closure in the neutron-rich region of the isotopic chain at $A=225$. The decay properties such as the $\alpha$-decay energy and corresponding half-life for three decay chains i.e. ${}^{243}$Fm, ${}^{245}$Fm and ${}^{247}$Fm are studied. Six different empirical formulae, namely; Viola-Seaborg, Royer, modified B. Alex Brown, Parkhomenko–Sobiczewski, Universal decay law and modified universal decay law are employed to ascertain the numerical dependency of the half-life for each decay energy. A comparative study of $Q$-values and half-lives for these decay chains gives a good signature of the calculated results. The half-life calculations of three decay chains suggest that ${}^{231}$Pu, ${}^{233}$Pu, ${}^{235}$Pu are shell closure nuclei having maximum half-lives, whereas ${}^{243}$Fm, ${}^{245}$Fm and ${}^{247}$Fm are shell stabilized with lower half-lives.

We employ the relativistic mean-field plus BCS (RMF+BCS) approach to study the behavior of $sd$-shell by investigating in detail the single particle energies, and proton and neutron density profiles along with the deformations and radii of even–even nuclei. Emergence of new shell closure, weakly bound structure and most recent phenomenon of bubble structure are reported in the $sd$-shell. ${}^{22}$C, ${}^{24}$O and ${}^{26}$S are found to have a weakly bound structure due to particle occupancy in 2$s_{1/2}$ state. On the other hand ${}^{22}$O, ${}^{34}$Ca and ${}^{34,48}$Si are found with depleted central density due to the unoccupied 2$s_{1/2}$ state and hence they are the potential candidates of bubble structure. ${}^{22}$C and ${}^{24}$O emerge as doubly magic with $N=16$ in accord with the recent experiments and ${}^{26}$S emerges as a new proton magic nucleus with $Z=16$. $N=14$ and $Z=14$ are predicted as magic numbers in doubly magic ${}^{22}$O, ${}^{34}$Ca and ${}^{34,48}$Si, respectively. These results are found in agreement with the recent experiments and have consistent with the other parameters of RMF and other theories.

Recent experimental observation of magicity in ${}^{78}$Ni has infused the interest to examine the persistence of the magic character across the $N=50$ shell gap in extremely neutron-rich exotic nucleus ${}^{78}$Ni in ground as well as excited states. A systematic study of Ni isotopes and $N=50$ isotones in ground state is performed within the microscopic framework of relativistic mean-field (RMF) theory and the triaxially deformed Nilsson–Strutinsky model (NSM). Ground state density distributions, charge form factors, radii, separation energies, pairing energies, single-particle energies and the shell corrections show strong magicity in ${}^{78}$Ni. Excited nuclei are treated within the statistical theory of hot rotating nuclei where the variations of level density parameter and entropy show significant magicity with a deep minima at $N=50$, which persists up to the temperatures $\approx$1.5–2MeV and then slowly disappears with increasing temperature. Rotational states are evaluated and effect of rotation on $N=50$ ($Z=20-30$) isotones are studied. Our results agree very well with the available experimental data and few other theoretical calculations.

A fully systematic study of even and odd isotopes $(281\le A\le 380)$ of $Z=121$ superheavy nuclei is presented in theoretical frameworks of Relativistic mean-field plus state dependent BCS approach and macroscopic–microscopic approach with triaxially deformed Nilsson-Strutinsky prescription. The ground state properties namely shell correction, binding energy, two- and one-proton and neutron separation energy, shape, deformation, density profile and the radius are estimated that show strong evidences for magicity in $N=164$, 228. Central depletion in the charge density due to large repulsive Coulomb field indicating bubble like structure is reported. A comprehensive analysis for the possible decay modes specifically $\alpha$-decay and spontaneous fission (SF) is presented and the probable $\alpha$-decay chains are evaluated. Results are compared with Finite Range Droplet Model (FRDM) calculations and the available experimental data which show excellent agreement.

Structural properties and the decay modes of the superheavy elements $Z=122,120$ and 118 are studied in a microscopic framework. We evaluate the binding energy, one- and two- proton and neutron separation energy, shell correction and density profile of even and odd isotopes of $Z=122,120,118$$(284\le A\le 352)$ which show a reasonable match with FRDM results and the available experimental data. Equilibrium shape and deformation of the superheavy region are predicted. We investigate the possible decay modes of this region specifically $\alpha$-decay, spontaneous fission (SF) and the $\beta$-decay and evaluate the probable $\alpha$-decay chains. The phenomena of bubble like structure in the charge density is predicted in ${}^{330}122$, ${}^{292,328}120$ and ${}^{326}118$ with significant depletion fraction around 20–24% which increases with increasing Coulomb energy and diminishes with increasing isospin ($N-Z$) values exhibiting the fact that the coulomb forces are the main driving force in the central depletion in superheavy systems.

By using a nonrelativistic independent particle model, we investigate the mechanism promoting 34 as new magic number. We carried out Hartree–Fock plus Bardeen–Cooper–Schrieffer and Quasi-particle Random Phase Approximation calculations by consistently using the same finite-range interaction in all the three steps of our approach. We used four Gogny-like interactions, with and without tensor terms. We find that the shell closure for $N=34$ neutrons appears in isotones with $Z<26$ protons. The smaller the proton number, the more evident is the shell closure at $N=34$. An ideal nucleus to investigate this effect should be ${}^{48}$Si, as it has been recently suggested. However, some discrepancies occur between the results obtained with the four effective interactions we used concerning the position of the two-neutron drip line and, therefore, the existence of ${}^{48}$Si. The experimental identification of this nucleus could shed light about the shell evolution in nuclei far from the stability valley and put stringent tests on nuclear structure theories.

We present a systematic description of the exotic features in the ground states of light nuclei from the stable valley to the drip lines. A study with the even and odd isotopes of Ne, Mg, Si, S and Ar has been performed using theoretical formalisms (i) Relativistic mean-field plus state-dependent BCS approach and (ii) Macroscopic–Microscopic (MM) approach using the triaxially deformed Nilsson–Strutinsky Method. The computed binding energies and one- and two-neutron separation energies using both the theories show magic character of $N=14,20,28$ and 40. The neutron and proton radii and the neutron densities show a well-developed neutron skin in the neutron-rich isotopes. The exotic phenomena such as weakly bound structures and the central density depletion characterized as bubble effect are explored. Our calculations for the single particle levels, density profiles and the charge form factors indicate bubble-like structures. Few new candidates of bubble nuclei are identified. Most of the nuclei in this region are found deformed with mostly prolate shape and few triaxial shapes while many nuclei exhibit the phenomenon of shape coexistence. Our results display a reasonable agreement between both the theories and the available experimental data.

In this work, we identify a unique and novel feature of central density depletion in both proton and neutron named as doubly bubble nuclei in $50\le Z(N)\le 82$ region. The major role of 2d-3s single-particle (s.p.) states in the existence of halo and bubble nuclei is probed. The occupancy in s.p. state 3s${}_{1/2}$ leads to the extended neutron density distribution or halo while the unoccupancy results in the central density depletion. By employing the Relativistic Mean-Field (RMF) approach along with NL3* parameter, the separation energies, s.p. energies, pairing energies, proton and neutron density profiles along with deformations of even–even nuclei are investigated. Our results are concise with few other theories and available experimental data. Emergence on new shell closure and the magicity of conventional shell closures are explored systematically in this yet unknown region.

We have performed a systematic study for the nuclear structure of superheavy nuclei with a special emphasis on the nuclei with possible central depletion of proton and neutron density in the mass region $\mathrm{\text{A}}\sim 300$ using the Relativistic Hartree–Bogoliubov (RHB) framework. It has been observed that in the case of neutron density distribution, the occurrence of central depletion is related to the occupancy of 4s orbital and it is found to decrease with increasing occupancy of the 4s orbital. On the other hand, in the case of proton density distribution, the central density depletion is mainly due to the lowering of weakly bound p-orbital states close to the continuum as it is energetically favored to lower the Coulomb repulsion in the case of superheavy nuclei. Also, occupation probability of the lower angular momentum states (p-orbitals) lying near the Fermi level is strongly suppressed due to the weak centrifugal barrier and strong Coulomb repulsion in comparison to large angular momentum states (contributing to surface region mainly), resulting in central density depletion. Among the considered cases in the present work, the maximum depletion is observed for ${}^{292}120$ and for ${}^{294}$Og under spherically symmetric and axially deformed cases, respectively.

The present contribution focuses on three recent experimental achievements obtained at the GANIL facility on the study of the N = 28 shell closure south to the doubly magic nucleus . First, the single particle energies of the neutron fp states in ⁴⁷Ar have been determined by transfer (d,p) reaction using a radioactive beam of . A reduction of the N = 28 gap and of the SO splittings of the f and p states is found. Second, an E0 isomer has been discovered in which is suggestive of a shape mixing. Third, the energy of the first 2⁺ state of has been obtained through in-beam γ-ray emission induced by a 2 protons knock-out reaction. Its low value, 770(19) keV, points to a large deformation there. The gradual change from spherical to deformation in the N = 28 isotones from Z = 20 to Z = 14 is ascribed to specific proton-neutron interactions and to enhanced quadrupole correlations. A global description of all the physics involved at N = 28 is derived along with experimental results.