Dispersive optical potential from an analysis of neutron single-particle energies in the Ti, Cr, and Fe isotopes featuring 20 to 50 neutrons

Neutron single-particle energies in unstable Ti, Cr, and Fe isotopes containing 20 to 26 neutrons were evaluated on the basis of experimental proton energies in the mirror-symmetric nuclei. The neutron single-particle energies in the 20 ? N ? 50 Ti, Cr, and Fe isotopes were calculated on the basis of the mean-field model with a dispersive optical potential, and the results were compared with available experimental data and with the results of estimations and calculations based on the relativistic mean-field model and on the multiparticle shell model with the GXPF1 interaction.     

Calculation of single-particle energies of bound nucleon states in nuclei with 40 ≤ <Emphasis Type="Italic">A</Emphasis> ≤ 208 using global parameters of dispersive optical model potential

Single-particle energies of bound neutron and proton states in nuclei with mass numbers 40 ≤ A ≤ 208 are calculated within the dispersive optical model with different sets of global parameters. The results of the calculation are compared with the experimental data and the predictions of the relativistic mean-field model.     

Nuclear structure investigation of neutron-rich Mn isotopes

Structural evolution of odd-even and odd-odd Mn isotopes from the valley of stability up to neutron dripline is studied in the framework of the self-consistent mean-field theory of Hartree–Fock–Bogoliubov. Three Skyrme effective interactions, namely, SLy4, SLy5 and SLy5T, are employed to investigate the tensor force effect on the ground-state properties. It is shown that the calculated quantities with the SLy4 interaction correctly reproduce the available experimental data and agree well with finite range droplet model and relativistic mean-field predictions. An inconsistency has been observed between the curves of the separation energies and that of the charge radius around N = 40. It is explained by the flatness of the potential energy curves in this region. The SLy5 and SLy5T results point to the necessity to refit all the Skyrme parameters after including the tensor terms.     

Deformed relativistic mean-field calculations on nuclei near Z = 50 with FSUGold

The ground-state properties of Sn, Te, Xe, and Ba isotopes have been systematically investigated in the framework of the deformed relativistic mean-field theory with the new parameter set FSUGold. The results show that FSUGold is as successful as NL3 ^* in reproducing the ground-state binding energies of the nuclei. The calculated two-neutron separation energies, quadrupole deformations, and root-mean-square (rms) charge radii are in good agreement with the experimental data. The parameter set FSUGold can successfully describe the shell effect of the neutron magic number N = 82 . Detailed discussions on the binding energies, two-neutron separation energies, quadrupole deformations, rms charge radii and “binding energies” of the last neutrons are given.     

Estimating the occupation probabilities of single-particle orbits in nuclei

Occupation probabilities of neutron and proton single-particle orbits are estimated for a number of spherical and close to spherical nuclei with 20 ≤ Z ≤ 50 and 20 ≤ N ≤ 82 near the Fermi energy. The estimates are made according to the formula of the BCS theory with single-particle energies calculated using the mean-field model with dispersive optical potential. The closeness of the occupation probabilities to 0 and 1 is demonstrated for nuclei with traditional and new magic numbers.     

Systematics of quadrupolar correlation energies

We calculate correlation energies associated with the quadrupole shape degrees of freedom with a view to improving the self-consistent mean-field theory of nuclear binding energies. Systematic results are presented for 605 even-even nuclei from mass number 16 to the heaviest whose mass has been measured, using the Skyrme SLy4 interaction and the generator coordinate method. Correlation energies range from 0.5 to 6.0 MeV, and their inclusion improves two qualitative deficiencies of the mean-field theory, namely, the exaggerated shell effect at neutron magic numbers and the failure of mean-field theory to describe mutually enhanced magicity. For the mass table as a whole, the quadrupolar correlations improve binding energies, separation energies, and separation energy differences by 20%30%.     

Evaluation and analysis of neutron single-particle energies in 78Ni nucleus

The evaluated single-particle energies of neutron states were obtained for doubly magic neutronrich nucleus ⁷⁸Ni. The evaluations were made by extrapolation of the experimental energies of stable nickel isotopes based on the mass regularities in the results of theoretical calculations of the energies, in particular, using the Koura-Yamada potential. The evaluated energies were analyzed by the mean-field model with dispersive optical potential; a good agreement between the calculated and evaluated energies was achieved.     

Shell structure of even-even nickel isotopes containing twenty to forty neutrons

Shell parameters of even-even nickel isotopes involving twenty to forty neutrons are analyzed, and the results of this analysis are presented. A detailed comparison of the results obtained by calculating, on the basis of the mean-field model with the Koura-Yamada potential and the dispersive optical potential, single-particle energies of proton and neutron subshells with experimental data on the isotopes ^{56,58,60,62,64,68}Ni and with evaluated data on the neutron-deficient isotopes ^48,50,52,54Ni is performed.     

Microscopic Studies on Ground State Properties of the Nucleus 100Sn

The average binding energy,the radius of proton distributions and the radius of neutron distributions for the nucleus ¹⁰⁰Sn have been calculated by the relativistic mean-field theory and the nonrelativistic mean-field theory.The numerical results by two methods have been compared and discussed.This is the first microscopic calculation on ¹⁰⁰Sn.     

Edge localized modes of cold neutrons in periodic condensed media

It is found that for certain energies of discreet cold neutrons, quasi-stationary eigen solutions of the corresponding Schrodinger equation, which are localized in the layer of a periodic medium, exist. The localization time of these solutions is strongly dependent on the layer thickness, being finite for a finite layer thickness and increasing indefinitely upon a infinite growth of the layer thickness as the third power of the layer thickness. The problem has been solved in the two-wave approximation of the dynamic diffraction theory for the neutron propagation direction coinciding with the periodicity axes (normal incidence of the neutron beam on the layer). The expressions for neutron eigenwave functions in a periodic medium, the reflection and transmission coefficients, and the neutron wavefunction in the layer as a function of the neutron energy incident on the layer have been determined. It turns out that for the certain discrete neutron energies, the amplitudes of the neutron wavefunction in the layer reach sharp maxima. The corresponding energies are just outside of the neutron stop band (energies forbidden for neutron propagation in the layer) and determine the energies of neutron edge modes (NEMs) localized in the layer, which are direct analogs of the optical edge modes for photonic crystals. The dispersion equation for the localized neutron edge modes has been obtained and analytically solved for the case of thick layers. A rough estimate for the localization length L is L ~(db N)^–1, where b is the neutron scattering length, d is the crystal period, and N is the density of nuclei in the crystal. The estimates of the localized thermal neutron lifetime show that acheaving of a lifetime close to the free neutron lifetime seems nonrealistic due to absorption of thermal neutrons and requires a perfect large size crystal. Nevertheless, acheaving the localized neutron lifetime exceeding by ~10⁴ times the neutron time of flight through the layer appears as experimentally attainable. The perspectives of the NEM observation are briefly discussed. It is proposed to use NEM for ultrahigh thermal neutron monochromatization by means of NEM excitation in perfect single crystals.     

Preequilibrium proton and α emission from neutron induced reactions in CsI

Angle integrated energy spectra of protons (plus deuterons) andα particles have been obtained from neutron bombardment of a CsI crystal serving both as detector and target. Measurements were performed for neutron energies between 14 and 32 MeV. An explanation of proton andα yields cannot be given by statistical evaporation, but requires the assumption of a preequilibrium mechanism dominating for projectile energies in excess of 20 MeV. For these neutron energies the hard components of the proton andα particle spectra can be described quantitatively with the hybrid and the quasi free scattering preequilibrium model, respectively.     

Scattering of fast neutrons on238U,average energy and angular distributions of fission neutrons

Angular distributions of neutrons elastically and inelastically scattered from²³⁸U have been measured with a time-of-flight spectrometer at seven incident neutron energies between 1.5 and 5.5 MeV. Inelastic angular distributions for groups of unresolved levels are given for incoming neutron energies of 1.5, 1.9 and 2.3 MeV. The corresponding neutron cross-sections were obtained relative to then-p scattering cross-sections. The average energies and angular distributions of the fission neutrons were extracted from the measured fission neutron spectra at 1.5,1.9 and 2.3 MeV. Cross-section calculations based on a spherical optical model have shown to be inadequate to describe the neutron-nucleus interaction in case of strong nuclear deformation. The experimental reality may be better approached, instead, if the calculations are made using a potential which takes into account the deformation of the target nucleus. Some of the present measurements are interpreted in this theoretical perspective.     

Messung des totalen Wirkungsquerschnitts von27Al für schnelle Neutronen mit Si(Li)-Detektoren

The total fast neutron cross section of²⁷Al has been determined by transmission measurements using Si(Li)-solid state detectors for neutron spectroscopy. The energies of the bombarding neutrons have been in the range betweenE _n=5,24 andE _n=7,26 MeV. A comparision has been made between the total cross sections obtained in this experiment and values obtained via the time-of-flight technique. At most neutron energies the agreement was within experimental errors quoted for the works being compared.     

Halo nuclei studied by relativistic mean-field approach

Density distributions of light neutron-rich nuclei are studied by using the relativistic mean-field approach. The effective interaction which parameterizes the recent Dirac-Brueckner-Hartree-Fock calculations of nuclear matter is used. The results are discussed and compared with the experimental observations with special reference to theneutron halo in the drip-line nuclei.     

The neutron drip line in the region of <Emphasis Type="Italic">N</Emphasis>=20 and <Emphasis Type="Italic">N</Emphasis>=28 closures

Experimental studies of neutron drip line nuclei are introduced. The neutron drip line in the oxygen-magnesium region has been explored by the projectile fragmentation of a ⁴⁸Ca beam. New neutron-rich isotopes, ³⁴Ne and ³⁷Na, have been observed together with some evidence for the particle instability of ³³Ne and ³⁶Na. Recent data on mass measurements of neutron-rich nuclei at GANIL and some characteristics of binding energies in this region are discussed. Nuclear binding energies are very sensitive to the existence of nuclear shells, and together with the measurements of instability of doubly magic nuclide ²⁸O, they provide information on changes in neutron shell closures of very neutron-rich isotopes from carbon up to calcium. The conclusion about a rearrangement in neutron shell closures is given. The spectroscopic measurements can reveal details of the underlying microscopic structures; in-beam γ-ray spectroscopy is an effective tool to check for shell closures. The results on the γ-ray energies of the first 2⁺ level in even-even nuclei for the range N=12–32 are discussed. The strength of N=20 and N=28 shells is variable in the region from carbon up to magnesium.     

Gamma-ray competition with neutron emission in the decay of 137I

Gamma-rays with energies above the neutron binding energy in ¹³⁷Xe have been observed at 3907 and 3994 keV in the decay of ¹³⁷I. Their combined intensity amounts to about 25% of the delayed neutron intensity and demonstrates that γ-ray widths are an important factor in defining the magnitude and energy distribution of the delayed neutron spectrum.     

Light nuclei near neutron and proton drip lines in relativistic mean-field theory

We have made a detailed study of the ground-state properties of nuclei in the light-mass region with atomic numbers Z = 10–22 in the framework of the relativistic mean-field (RMF) theory. The nonlinear σω model with scalar self-interaction has been employed. The RMF calculations have been performed in an axially deformed configuration using the force NL-SH. We have considered nuclei about the stability line as well as those close to proton and neutron drip lines. It is shown that the RMF results provide good agreement with the available empirical data. The RMF predictions also show reasonably good agreement with those of the mass models. It is observed that nuclei in this mass region are found to possess strong deformations and exhibit shape changes all along the isotopic chains. The phenomenon of shape coexistence is found to persist near the stability line as well as near the drip lines. It is shown that the magic number N = 28 is quenched strongly, thus enabling the corresponding nuclei to assume strong deformations. Nuclei near the neutron and proton drip lines in this region are also shown to be strongly deformed.     

Ground-state properties of neutron magic nuclei

A systematic study of the ground-state properties of the entire chains of even–even neutron magic nuclei represented by isotones of traditional neutron magic numbers N = 8, 20, 40, 50, 82, and 126 has been carried out using relativistic mean-field plus Bardeen–Cooper–Schrieffer approach. Our present investigation includes deformation, binding energy, two-proton separation energy, single-particle energy, rms radii along with proton and neutron density profiles, etc. Several of these results are compared with the results calculated using nonrelativistic approach (Skyrme–Hartree–Fock method) along with available experimental data and indeed they are found with excellent agreement. In addition, the possible locations of the proton and neutron drip-lines, the (Z, N) values for the new shell closures, disappearance of traditional shell closures as suggested by the detailed analyzes of results are also discussed in detail.     

R-matrix formulation and phase shifts for n-He and p-He scattering for energies up to 20 MeV

An R-matrix formulation for a single level with a background approximation has been used to analyse n-⁴He and p-⁴He elastic scattering data below the inelastic thresholds near 22 MeV. For every partial wave a single level and a distant pole contribution constant with energy has been employed. Simple relations between neutron and proton scattering parameters have been sought to possibly derive more dependable values for neutron phase shifts and analysing powers at energies where little experimental information exists. The R-matrix parameters corresponding to ⁵He and ⁵Li ground and 1st excited states, phase shifts up to 20 MeV and neutron analysing powers up to 15 MeV are given in tabular form and are compared to results of earlier analyses. Differences in n-⁴He phase shifts are discussed and shown to be due to a scarcity of accurate neutron scattering data above 11 MeV. Some typical fits to n-⁴He scattering data are shown.     

On the mechanism of the reactions24,25,26Mg(n,α)21,22,23Ne at neutron energies near 14 MeV

Differential cross sections of the reactions²⁴Mg(n,α)²¹Ne,²⁵Mg(n,α)²²Ne, and²⁶Mg(n,α)²³Ne have been measured at neutron energies of 13.19,13.93 and 14.33 MeV, at 13.93 and 14.33 MeV, and at 13.47 and 13.93 MeV, respectively. In forward direction, differential excitation functions of those reactions have been measured at energies between 12.67 and 16.05 MeV. The results are analysed in terms of direct-reaction and compound-nucleus theories.