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Nuclear level density parameter is one of the fundamental quantities required for finding the nuclear level density. The most essential ingredient for the theoretical analysis of nuclear reactions is nuclear level density. This work is a theoretical study on the variation of collective nuclear level density parameter of certain even-even actinides. This calculations were performed by using phenomenological models of level density. The computational code TALYS 1.9 has been made use of for this purpose. Here, we calculated the collective nuclear level density parameter of 268 - 278 Th, 270 - 280 U, 272 - 282 Pu, 274 - 284 Cm, 278 - 288 Cf, 278 - 288 Fm and 280 - 290 No, at neutron separation energy. Variation of collective level density parameter with different mass number is estimated for these selected nuclei. These studies show that nuclear level density parameter is minimum at neutron number N = 180 and 184 for these systems studied. Apart from that, the level density parameters decrease towards N = 184 . [ABSTRACT FROM AUTHOR]

In this paper, we have analyzed the ground state structural properties of fermium-isotopes in the mass range 2 2 1 ≤ A ≤ 2 7 9 within the relativistic mean-field with NL3 ∗ 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 = 2 2 5. The decay properties such as the α -decay energy and corresponding half-life for three decay chains i.e. 2 4 3 Fm, 2 4 5 Fm and 2 4 7 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 2 3 1 Pu, 2 3 3 Pu, 2 3 5 Pu are shell closure nuclei having maximum half-lives, whereas 2 4 3 Fm, 2 4 5 Fm and 2 4 7 Fm are shell stabilized with lower half-lives. [ABSTRACT FROM AUTHOR]

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 A ∼ 3 0 0 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 2 9 2 1 2 0 and for 2 9 4 Og under spherically symmetric and axially deformed cases, respectively. [ABSTRACT FROM AUTHOR]

The nuclear structure of 51Ar, an uncharted territory so far, was studied by the (p,2p) reaction using γ-ray spectroscopy for the bound states and the invariant mass method for the unbound states. Two peaks were detected in the γ-ray spectrum and six peaks were observed in the 50Ar+n relative energy spectrum. Comparing the results to our shell-model calculations, two bound and six unbound states were established. Three of the unbound states could only be placed tentatively due to the low number of counts in the relative energy spectrum of events associated with the decay through the first excited state of 50Ar. The low cross sections populating the two bound states of 51Ar could be interpreted as a clear signature for the presence of significant subshell closures at neutron numbers 32 and 34 in argon isotopes. It was also revealed that due to the two valence holes, unbound collective states coexist with individual-particle states in 51Ar.

Shell closures and their associated magic numbers of nucleons provide a unique means for studying the structure of exotic nuclei far from stability. An experiment was recently performed at the National Superconducting Cyclotron Laboratory to measure resonant elastic proton scattering on 46Ar in inverse kinematics in the region containing isobaric analogue states of 47Ar, an N=29 nucleus with one neutron above the N=28 shell closure. Four candidate resonances were observed: one corresponding to the 3/2− ground state of 47Ar, another corresponding to its 1/2− first excited state, and two that likely correspond to states in the 47K compound nucleus. The observed properties of the ground state resonance were compatible with values from the literature, but a significantly lower spectroscopic factor was found for the 1/2− state resonance.

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 5 0 ≤ Z (N) ≤ 8 2 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. [ABSTRACT FROM AUTHOR]

There has been plenty of empirical evidence which shows that the single-particle picture holds to a good approximation in atomic nuclei. In this picture, protons and neutrons move independently inside a mean-field potential generated by an interaction among the nucleons. This leads to the concept of nuclear shells, similar to the electronic shells in atoms. In particular, the magic numbers due to closures of the nucleonic shells, corresponding to noble gases in elements, have been known to play an important role in nuclear physics. Here we propose a periodic table for atomic nuclei, in which the elements are arranged according to the known nucleonic shells. The nuclear periodic table clearly indicates that nuclei in the vicinity of the magic numbers can be understood in terms of a shell closure with one or two additional nucleons or nucleon holes, while nuclei far from the magic numbers are characterized by nuclear deformation. [ABSTRACT FROM AUTHOR]

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 = 1 4 , 2 0 , 2 8 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. [ABSTRACT FROM AUTHOR]

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 = 3 4 neutrons appears in isotones with Z < 2 6 protons. The smaller the proton number, the more evident is the shell closure at N = 3 4. An ideal nucleus to investigate this effect should be 4 8 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 4 8 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. [ABSTRACT FROM AUTHOR]

Structural properties and the decay modes of the superheavy elements Z = 1 2 2 , 1 2 0 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 = 1 2 2 , 1 2 0 , 1 1 8 (2 8 4 ≤ A ≤ 3 5 2) 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 α -decay, spontaneous fission (SF) and the β -decay and evaluate the probable α -decay chains. The phenomena of bubble like structure in the charge density is predicted in 3 3 0 1 2 2 , 2 9 2 , 3 2 8 1 2 0 and 3 2 6 1 1 8 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. [ABSTRACT FROM AUTHOR]

We investigate the mass dependence of the nuclear structure and the effective symmetry energy for the Kr and Ba nuclei. The axially deformed self‐consistent relativistic mean field with the nonlinear NL3* parameter set is used in the analysis. The coherent density fluctuation model is adopted to formulate the nuclear matter observables such as symmetry energy, neutron pressure, and symmetry energy curvature of finite nuclei as a function of the radius. We found a notable signature of the shell/subshell closure at N = 50 and 82 for the isotopic chains of Kr and Ba nuclei, respectively. [ABSTRACT FROM AUTHOR]

A fully systematic study of even and odd isotopes (2 8 1 ≤ A ≤ 3 8 0) of Z = 1 2 1 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 = 1 6 4 , 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 α -decay and spontaneous fission (SF) is presented and the probable α -decay chains are evaluated. Results are compared with Finite Range Droplet Model (FRDM) calculations and the available experimental data which show excellent agreement. [ABSTRACT FROM AUTHOR]

Recent experimental observation of magicity in 7 8 Ni has infused the interest to examine the persistence of the magic character across the N = 5 0 shell gap in extremely neutron-rich exotic nucleus 7 8 Ni in ground as well as excited states. A systematic study of Ni isotopes and N = 5 0 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 7 8 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 = 5 0 , which persists up to the temperatures ≈ 1.5–2 MeV and then slowly disappears with increasing temperature. Rotational states are evaluated and effect of rotation on N = 5 0 ( Z = 2 0 − 3 0 ) isotones are studied. Our results agree very well with the available experimental data and few other theoretical calculations. [ABSTRACT FROM AUTHOR]

Shell closures and their associated magic numbers of nucleons provide a unique means for studying the structure of exotic nuclei far from stability. An experiment was recently performed at the National Superconducting Cyclotron Laboratory to measure resonant elastic proton scattering on 46 Ar in inverse kinematics in the region containing isobaric analogue states of 47 Ar, an N = 29 nucleus with one neutron above the N = 28 shell closure. Four candidate resonances were observed: one corresponding to the 3 / 2 − ground state of 47 Ar, another corresponding to its 1 / 2 − first excited state, and two that likely correspond to states in the 47 K compound nucleus. The observed properties of the ground state resonance were compatible with values from the literature, but a significantly lower spectroscopic factor was found for the 1 / 2 − state resonance. [ABSTRACT FROM AUTHOR]

We employ the relativistic mean-field plus BCS (RMF+BCS) approach to study the behavior of -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 -shell. C, O and S are found to have a weakly bound structure due to particle occupancy in 2 state. On the other hand O, Ca and Si are found with depleted central density due to the unoccupied 2 state and hence they are the potential candidates of bubble structure. C and O emerge as doubly magic with in accord with the recent experiments and S emerges as a new proton magic nucleus with . and are predicted as magic numbers in doubly magic O, Ca and Si, respectively. These results are found in agreement with the recent experiments and have consistent with the other parameters of RMF and other theories. [ABSTRACT FROM AUTHOR]

Collinear laser spectroscopy was performed on Zn ( Z = 30 ) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N = 33 – 49 , allowed the measurement of nuclear spins for the ground and isomeric states in odd- A neutron-rich nuclei up to N = 50 . Exactly one long-lived (>10 ms) isomeric state has been established in each 69 – 79 Zn isotope. The nuclear magnetic dipole moments and spectroscopic quadrupole moments are well reproduced by large-scale shell–model calculations in the f 5 pg 9 and fpg 9 d 5 model spaces, thus establishing the dominant term in their wave function. The magnetic moment of the intruder I π = 1 / 2 + isomer in 79 Zn is reproduced only if the ν s 1 / 2 orbital is added to the valence space, as realized in the recently developed PFSDG-U interaction. The spin and moments of the low-lying isomeric state in 73 Zn suggest a strong onset of deformation at N = 43 , while the progression towards 79 Zn points to the stability of the Z = 28 and N = 50 shell gaps, supporting the magicity of 78 Ni. [ABSTRACT FROM AUTHOR]

Evolution of shells has been studied through fluctuations of particle numbers, pairing energies of large number of isotopes and isotones of nuclei evaluated through Skyrme-Hartree-Fock theory after inclusion of optimized tensor interaction. For neutron rich isotopes of Mg, Si, S and Ar no indication of shell closure at N = 28 has been observed. Calculations show occurrence of a doubly shell closed nucleus Fl . [ABSTRACT FROM AUTHOR]

We investigate the nature and impact of shell effects on nuclear level density (NLD) and particle emission probability as a function of temperature in a microscopic theoretical framework of Statistical Model for nuclei ranging from neutron deficient to neutron rich isotopes of Z= 27−35. Critical temperatures are traced for neighbouring even, odd, closed shell and mid−shell nuclei which respond to excitations differently due to their varying stability and structural effects. Importance of the shell effects and shell correction energy is reflected significantly in NLD variation which slowly diminishes with increasing excitation energy indicating the quenching of shell effects. The enhancement of LD parameter with the deformation and rotation and the fade out of enhancement with increasing excitations has been shown. The weakening of magicity of N=28 near the proton drip line has been observed in the inverse level density parameter 'K'(= A/a) and β variation though it is usually uncommon to see this effect in excited nuclei. Variation of our calculated NLD for odd 69As and even 70Ge exhibits structural effects and agrees very well with the variation of experimental values. Our evaluated level density parameter 'a' values are compared with RIPL-2 (Reference Input Parameter Library) data which show good agreement. [ABSTRACT FROM AUTHOR]

The deformed configurations and rotational band structures in N = 50 Ge and Se nuclei are studied by deformed Hartree-Fock with quadrupole constraint and angular momentum projection. Apart from the 'almost' spherical HF solution, a well-deformed configuration occurs at low excitation. A deformed well-mixed Ω = 1/2 neutron orbit comes down in energy (from the shell above N = 50) to break the N = 50 spherical shell closure. A K = 7 isomer is predicted in Se at fairly low excitation energy. At higher excitation energies (8 MeV), a deformed band with Ω = 7/2- 1/2 (based on h) neutron 1p-1h excitation, for Ge and Se, is shown in our calculation. Our study gives insight into possible deformed structures at spherical shell closure. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study of shell closures around N and through beta decay Q-values, one nucleon separation energies and excited states is presented for different isospin chains. Shell closure at is found to be absent in neutron-rich nuclei (contrary to some existing discussions) but is indicated in nuclei with within errors. The persistence of the N and shell closure is observed, together with evidence of sub-shell closure at in neutron-rich nuclei. The sub-shell closure at , that exists for neutron-rich nuclei, is found to disappear for . [Copyright &y& Elsevier]

The TITAN facility at TRIUMF-ISAC will use four ion traps with the primary goal of determining nuclear masses with high precision, particularly for short lived isotopes with lifetimes down to approximately 10 ms. The design value for the accuracy of the mass measurement is 1 ×10 − 8. The four main components in the facility are an RF cooler/buncher (RFCT) receiving the incoming ion beam, an electron beam ion trap (EBIT) to breed the ions to higher charge states, a cooler Penning trap (CPET) to cool the highly charged ions, and finally the measurement Penning trap (MPET) for the precision mass determination. Additional goals for this system are laser spectroscopy on ions extracted from the RFCT and beta spectroscopy in the EBIT (in Penning trap mode) on ions that are purified using selective buffer gas cooling in the CPET. The physics motivation for the mass measurements are manifold, from unitarity tests of the CKM matrix to nuclear structure very far from the valley of stability, nuclear astrophysics and the study of halo-nuclei. As a first measurement the mass of 11Li will be determined. With a lifetime of 8.7 ms and a demonstrated production rate of 4×104 ions/sec at ISAC the goal for this measurement at TITAN is a relative uncertainty of 5×10 − 8. This would check previous conflicting measurements and provide information for nuclear theory and models. [ABSTRACT FROM AUTHOR]

Motivated by much recent discussion of the N=8 neutron shell closure, we review the theoretical description of 12Be within a three-body (n+n+10Be) model with core excitation. Agreement with recently deduced 〈11Be|12Be〉 spectroscopic factors requires a smaller deformation of the 10Be core in 12Be than in 11Be, with a reduced role for core excitation. Observables for the ground state and 2+, 1− and 0+2 excited states of 12Be are presented. Limitations and improvements of the model are discussed. [Copyright &y& Elsevier]

The nuclear structure of 51Ar, an uncharted territory so far, was studied by the (p,2p) reaction using γ -ray spectroscopy for the bound states and the invariant mass method for the unbound states. Two peaks were detected in the γ -ray spectrum and six peaks were observed in the 50Ar+n relative energy spectrum. Comparing the results to our shell-model calculations, two bound and six unbound states were established. Three of the unbound states could only be placed tentatively due to the low number of counts in the relative energy spectrum of events associated with the decay through the first excited state of 50Ar. The low cross sections populating the two bound states of 51Ar could be interpreted as a clear signature for the presence of significant subshell closures at neutron numbers 32 and 34 in argon isotopes. It was also revealed that due to the two valence holes, unbound collective states coexist with individual-particle states in 51Ar. [ABSTRACT FROM AUTHOR]