Spurious Shell Closures in the Relativistic Mean Field Model

Following a previous systematic theoretical study of the ground-state properties of over 7000 nuclei from the proton drip line to the neutron drip line in the relativistic mean field model [Prog. Theor. Phys. 113 （2005） 785], which is in fair agreement with existing experimental data, we observe a few spurious shell closures, i.e. proton shell closures at Z = 58 and Z = 92. These spurious shell closures are found to persist in all the effective forces of the relativistic mean field model, e.g. TMA, NL3, PKDD and DD-ME2.     

Nuclear chart in covariant density functional theory with dynamic correlations: From oxygen to tin

Nuclear masses of even-even nuclei with the proton number 8≤Z≤50(O to Sn isotopes)from the proton drip line to neutron drip line are investigated using the triaxial relativistic Hartree-Bogoliubov theory with the relativistic density functional PC-PK1.Further,the dynamical correlation energies(DCEs)associated with the rotational motion and quadrupole-shaped vibrational motion are taken into account by the five-dimensional collective Hamiltonian(5DCH)method.The root-mean-square deviation with respect to the experimental masses reduces from 2.50 to 1.59 MeV after the consideration of DCEs.The inclusion of DCEs has little influence on the position of drip lines,and the predicted numbers of bound even-even nuclei between proton and neutron drip lines from O to Sn isotopes are 569 and 564 with and without DCEs,respectively.     

Effects of pairing correlation on neutron drop

In this work, the effects of the pairing correlation on the properties of neutron drops N=6-50 trapped in a harmonic oscillator potential with ω = 10 Me V are investigated by comparing the results given by the Skyrme Hartree-Fock and Hartree-FockBogoliubov theories with the density-dependent delta interaction(DDDI) pairing force. The results showed that the pairing correlation slightly made the neutron drops more bound, and increased the central neutron density, the spin-orbit and pseudo spin-orbit splittings. Thus, the pairing correlation must be accounted for to improve the Skyrme functional compared with the ab initio calculations. Furthermore, although the single-particle energy gaps with or without pairing were similar, the shell closures varied due to pair scattering. Here, the shell closures in neutron drops using the Sk M* parameter set and DDDI pairing force were found at N=8, 16, and 32.     

β-delayed proton decays near the proton drip line

Simply speaking, the drip line is the margin in chart of the nuclides where the nu-clides with the lower limits of detectable lifetime survive. The N/Z ratios of the nuclides on the drip line are extreme. Synthesis of the nuclei near the drip line and study of their exotic decays deal with the physics under extreme conditions, and therefore become one of the frontiers in nuclear physics today. The rare-earth nuclei near the proton drip line have been predicted to be highly deformed[1]. They a…     

Shell-model studies of the N=14 and 16 shell closures in neutron-rich nuclei

Shell-model studies on the N =14 and 16 shell closures in neutron-rich Be, C, O and Ne isotopes are presented. We calculate, with the WBT interaction, the excited states in these nuclei. The calculations agree with recent experiment data. Excited energies and B(E2) values are displayed to discuss the shell closures. Our results support the N =16 shell closure in these isotopes, while indicating a disappearance of N =14 shell closure in Be and C isotopes.     

Shell-model studies of the N=14 and 16 shell closures in neutron-rich nuclei

Shell-model studies on the N=14 and 16 shell closures in neutron-rich Be, C, O and Ne isotopes are presented. We calculate, with the WBT interaction, the excited states in these nuclei. The calculations agree with recent experiment data. Excited energies and B(E2) values are displayed to discuss the shell closures. Our results support the N=16 shell closure in these isotopes, while indicating a disappearance of N=14 shell closure in Be and C isotopes.     

Shape transitions in proton-rich Ho and Tm isotopes

Total Routhian Surface (TRS) calculations have been performed for even-even nuclei along proton drip line to study nuclear ground-state deformations, as well as the odd proton nuclei Ho and Tm isotopes. The drip line nuclei show the expected shape transition with the shell e?ects. Ground-state shape changes from prolate to oblate at 143Ho and 145Tm in these two isotopes, which is due to the γ instability around N =76.     

Shape transitions in proton-rich Ho and Tm isotopes

Total Routhian Surface (TRS) calculations have been performed for even-even nuclei along proton drip line to study nuclear ground-state deformations, as well as the odd proton nuclei Ho and Tm isotopes. The drip line nuclei show the expected shape transition with the shell effects. Ground-state shape changes from prolate to oblate at ¹⁴³Ho and ¹⁴⁵Tm in these two isotopes, which is due to the γ instability around N=76.     

Properties and structure of N=Z nuclei within relativistic mean field theory

The axially deformed relativistic mean field theory with the force NLSH has been performed in the blocked BCS approximation to investigate the properties and structure of N=Z nuclei from Z=20 to Z=48. Some ground state quantities such as binding energies, quadrupole deformations, one/two-nucleon separation energies, root-mean-square （rms） radii of charge and neutron, and shell gaps have been calculated. The results suggest that large deformations can be found in medium-heavy nuclei with N=Z=38-42. The charge and neutron rms radii increase rapidly beyond the magic number N=Z=28 until Z=42 with increasing nucleon number, which is similar to isotope shift, yet beyond Z=42, they decrease dramatically as the structure changes greatly from Z=42 to Z=43. The evolution of shell gaps with proton number Z can be clearly observed. Besides the appearance of possible new shell closures, some conventional shell closures have been found to disappear in some region. In addition, we found that the Coulomb interaction is not strong enough to breakdown the shell structure of protons in the current region.     

Structural, electronic, and magnetic properties of boron cluster anions doped with aluminum: BnAl- (2≤n≤9)

The geometrical structures, relative stabilities, electronic and magnetic properties of small B n Al (2 ≤ n ≤ 9) clusters are systematically investigated by using the first-principles density functional theory. The results show that the Al atom prefers to reside either on the outer-side or above the surface, but not in the centre of the clusters in all of the most stable B n Al (2 ≤ n ≤ 9) isomers and the one excess electron is strong enough to modify the geometries of some specific sizes of the neutral clusters. All the results of the analysis for the fragmentation energies, the second-order difference of energies, and the highest occupied-lowest unoccupied molecular orbital energy gaps show that B 4 Al and B 8 Al clusters each have a higher relative stability. Especially, the B 8 Al cluster has the most enhanced chemical stability. Furthermore, both the local magnetic moments and the total magnetic moments display a pronounced odd-even oscillation with the number of boron atoms, and the magnetic effects arise mainly from the boron atoms except for the B 7 Al and B 9 Al clusters.     

Proton Fraction in Neutron Star Matter and Three-Body Force Effects

The three-body force effects on the equation of state and its iso-spin dependence of asymmetric nuclear matter and on the proton fraction in neutron star matter have been investigated[1] within Brueckner Hartree-Fock (BHF) approach by using a microscopic three-body force. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs. isospin asymmetry β=(N-Z)/A is fulfilled in the whole asymmetry range 0 ≤β ≤1 and also up to high density. The three-body force provides a strong enhancement of symmetry energy at high density in agreement with relativistic approaches. Thecalculated proton fraction in β stable neutron star matter is given in Fig.l, where the thick solid line is the BHF prediction using AV18 TBF, while the dotted one is the BHF result using AVis. The thin solid line is the prediction of the Dirac-Brueckner approach taken from Ref.[2]. The results extracted according to the phenomenological paramete rizations of the symmetry energy suggested in Ref.[3] are also plotted. It is seen from     

Structures and Electronic Properties of CuN （N≤13） Clusters

A systematic study on the structures and electronic properties of copper clusters has been performed using the density functional theory. In the calculation, there are many isomers near the ground state for small copper clusters. Our results show that the three-dimensional isomers of copper clusters start from Cu7 cluster and then show a tendency to form more compact structures. The results of the formation energy and the second derivative of binding energy with duster size show that besides N = 8, N =11 is also a magic number. Furthermore, it is the first time to find that the ground state of 11-atom clusters is a biplanar structure as same as the 13-atom cluster. The clear odd-even alternation as cluster size for the formation energy indicates the stability of electronic close shell existed in the range studied.     

K Shell and L Subshell Photoeffect Cross-Sections of Some Elements in the Atomic Range 50≤Z≤65 at 59.5 keV

In this study,K and L shell photoeffect cross-sections were measured for the elements in the range of 50≤Z≤65at 59.5keV.These photoeffect cross-sections were measured by using the experimentalσKαproduction cross-section values measured in this paper and two different K shell fluorescence yield values in the literature.The results were compared with the calculated theoretical values.The values were plotted versus atomic number.     

Calculated Optical Properties of Dielectric Shell Coated Gold Nanorods

Optical absorption spectra of dielectric shell coated gold nanorods are simulated using the discrete dipole ap- proximation method. The influence of the aspect ratio, shell thickness, dielectric constant of the shell, and surrounding medium on the longitudinal resonance mode is investigated. It is found that the coated dielectric shell does not affect the trend in the dependence of resonance position on the aspect ratio, while it broadens the resonant line width and reduces the sensitivity of plasmon resonance in response to changes of the surrounding medium. F~arthermore, the difference of dielectric constants between the shell and surrounding medium plays an important role in determining the resonance position. The screening effect of the dielectric shell tends to be less apparent for a thicker shell thickness.Optical absorption spectra of dielectric shell coated gold nanorods are simulated using the discrete dipole ap- proximation method. The influence of the aspect ratio, shell thickness, dielectric constant of the shell, and surrounding medium on the longitudinal resonance mode is investigated. It is found that the coated dielectric shell does not affect the trend in the dependence of resonance position on the aspect ratio, while it broadens the resonant line width and reduces the sensitivity of plasmon resonance in response to changes of the surrounding medium. F~urthermore, the difference of dielectric constants between the shell and surrounding medium plays an important role in determining the resonance position. The screening effect of the dielectric shell tends to be less apparent for a thicker shell thickness.     

Properties of Zr hypernuclei in deformed Skyrme Hartree-Fock approach

Properties of the even-N Zr isotopes and their corresponding single-Λ and double-Λ hypernuclei are studied in the deformed Skyrme-Hartree-Fock approach. Binding energy, the two-neutron separation energies, radii are studied from beta-stable zone to the neutron drip line in this paper. The neutron drip line nuclei predicted with SLy4 and SkI4 interactions are 122Zr and 138Zr, respectively. The neutron drip line of single-Λ and double-Λ hypernuclei are Λ139Zr and 2Λ142 Zr with SkI4 interaction, respectively. The predicted hyperon drip line hypernuclei with 80Zr and 138Zr cores are 20Λ100Zr and 50Λ188Zr, respectively.     

Structures and electronic properties of AUn-1Cu and AUn （n ≤ 9） clusters

A systematic study on the structure and electronic properties of gold clusters doped each with one copper atom has been performed using the density functional theory. The average bond lengths in the Aun-1Cu （n ≤ 9） bimetallic clusters are shorter than those in the corresponding pure gold clusters. The ionization potentials of the bimetallic clusters Aun-1Cu （n 〈 9） are larger than those of the corresponding homoatomic gold clusters except for Aus. The energy gaps of the Au-Cu binary clusters are narrower than those of the Aun clusters except AuCu and Au3Cu. No obvious even-odd effect exists in the variations of the electron affinities and ionization potentials for the Aun-1Cu （n ≤ 9） clusters, which is in contrast to the case of gold clusters Aun.     

Universality principle and the development of classical density functional theory

The universality principle of the free energy density functional and the ‘test particle' trick by Percus are combined to construct the approximate free energy density functional or its functional derivative. Information about the bulk fluid radial distribution function is integrated into the density functional approximation directly for the first time in the present methodology. The physical foundation of the present methodology also applies to the quantum density functional theory.     

Signatures of shell evolution in alpha decay across the N=126 shell closure

Within the alpha-cluster model, we particularly investigate the alpha decay of exotic nuclei in the vicinity of the N = 126 neutron shell plus the Z = 82 proton shell. The systematics of alpha-preformation probability(P_α),as an indicator of the shell effect, is deduced from the ratio of the experimental decay width to the calculated one.Through the comparative analysis of the P_α trend in the N = 124-130 isotonic chain, the N = 126 and Z = 82 shell closures are believed to strongly affect the formation of the alpha particle before its penetration. Additionally, the P_α variety in Po and Rn isotopes is presented as another proof for such an influence. More importantly, it may be concluded that the expected neutron(or proton) shell effect gradually fades away along with the increasing valence proton(or neutron) number. The odd-even staggering presented in the P_α value is also discussed.     

Electronic band transformation from indirect gap to direct gap in Si-H compound

The electronic band structures of periodic models for Si-H compounds are investigated by the density functional theory.Our results show that the Si-H compound changes from indirect-gap semiconductor to direct-gap semiconductor with the increase of H content.The density of states,the partial density of states and the atomic charge population are examined in detail to explore the origin of this phenomenon.It is found that the Si-Si bonds are affected by H atoms,which results in the electronic band transformation from indirect gap to direct gap.This is confirmed by the nearest neighbour semi-empirical tight-binding (TB) theory.     

Density Functional Study of Cationic and Anionic Ag_mCu_n (m + n ≤ 5) Clusters

The structural and energetic properties of bimetallic Ag m Cu n clusters (m + n ≤ 5) in the cationic and anionic charged states have been investigated by density functional theory with relativistic effective core potentails.The stable cationic pentamers have three-dimensional structures in contrast to anionic clusters assume planar structures.For the given cluster size the electron affinities decrease as the Cu content increases,while no clear trend can be found in adiabatic ionization potentials.The binding energy per atom also increases with the increasing Cu content and follows the order anion cation.The most probable dissociation channels of the clusters considered are also discussed.