Isospin dependence of proton and neutron radii within relativistic mean field theory

The proton and neutron radii of even-even β-stable nuclei with A ⩾ 40 and a few chains of isotopes with Z = 50, 56, 82, 94 protons and isotones with N = 50, 82, 126 neutrons are analyzed. The average isospin dependence of the radii evaluated within the relativistic mean field theory is studied. A simple, phenomenological formula for neutron radii is proposed.     

Magic numbers in superheavy elements

The energy density method is used to study the magic character of neutron and proton numbers corresponding to N > 126 and Z > 82. It is found that N = 184 and N = 228 are the next neutron magic numbers. For the protons, however, no sign of a shell closure appears for 82 < Z ? 130. Some simple criteria for the β^? - and α-stability of N = 184 and N = 228 isotones are also discussed.     

Laserspectroscopic studies of collective properties of neutron deficient Ba Nuclei

Isotope shifts and hyperfine structure of the BaI resonance-line (λ=553.6 nm) have been measured by dye laser induced resonance fluorescence on an atomic beam for^{135m, 129g, 129m, 126}Ba thus extending previous high resolution measurements of neutron deficient Ba nuclides (N<82). The experimental results, now available for 16Ba isotopes and isomers withA=140?126, are used to deduce differences of rms charge radii, magnetic dipole and electric quadrupole moments. While the groundstates display a pronounced odd-even staggering the h 11/2^? isomers^135mBa and^133mBa show a decreased staggering. Conspicuously the isomer shift of theg 7/2⁺ isomer^129m Ba proves to be negative. The nuclear structure information is discussed in the context of gammaspectroscopic studies of transitional nuclei with 50<N,Z<82 and on the basis of a quasi-particle-plus-triaxial rotor model. The isotope shift discrepancy observed is fairly well described by the droplet model.     

Quadrupole moments of spherical semi-magic nuclei within the self-consistent Theory of Finite Fermi Systems

The quadrupole moments of odd neighbors of semi-magic lead and tin isotopes and N = 50 , N = 82 isotones are calculated within the self-consistent Theory of Finite Fermi Systems based on the Energy Density Functional by Fayans et al. Two sets of published functionals are used to estimate systematic errors of the present self-consistent approach. They differ by the spin-orbit and effective tensor force parameters. The functional DF3-a leads to quadrupole moments in reasonable agreement with the experimental ones for most, but not all, nuclei considered.     

Nuclear spins,moments, and changes of the mean square charge radii of140−153Eu

The hyperfine structures and isotope shifts of 14 isotopes of Eu (Z=63) in the mass range 140≦A≦153, partly with isomeric states, have been measured in the atomic transitions at 4,594 Å and 4,627 Å, using the technique of collinear fast-beam laser spectroscopy at the ISOLDE facility at CERN. The nuclear spins, the magnetic dipole and electric quadrupole moments, and the changes in the mean square charge radii have been evaluated. These nuclear parameters clearly reflect the effects of theN=82 neutron-shell closure in the single-proton hole states with respect to the semi-magic gadolinium (Z=64), and theN=88?90 shape transition.     

Alpha decay chains from superheavy nuclei

Magic islands for extra-stable nuclei in the midst of the sea of fission-instability were predicted to be around Z=114, 124 or, 126 with N=184, and Z=120, with N=172. Whether these fission-survived superheavy nuclei with high Z and N would live long enough for detection or, undergo α-decay in a very short time, remains an open question. α-decay half lives of nuclei with 130≥Z≥100 have been calculated in a WKB framework using density-dependent M3Y interaction with Q-values from different mass formulae. The results are in excellent agreement with the experimental data. Fission survived Sg nuclei with Z=106, N=162 is predicted to have the highest α-decay half life (∼3.2 h) in the Z=106-108, N=160-164 region called small island/peninsula. Superheavy nuclei with Z>118 are found to have α-decay half lives of the order of microseconds or less.     

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.     

Is there neutron-proton pairing in medium heavy nuclei?

Present knowledge of the proton and neutron pairing energies Δ_p and Δ_n, deduced from nuclear masses, is reviewed and an attempt is made to find general trends in the data. The analysis shows that, besides the well-known smooth slow decrease with A, the pairing energies also contain a symmetry energy-like dependence on the neutron excess $\text{(N?Z)}\text{A}$. The trends is most pronounced in the shell 50<Z<82, 82<N<126 where both pairing energies decrease by a factor of almost two between the most neutron deficient and the most neutron rich nuclei. The same tendency persists in other mass regions, but is not a universal one. An empirical expression for Δ, that is more accurate than the value $\text{12A}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{MeV}$ usually assumed, is proposed.     

A microscopic explanation of the isotonic multiplet at N = 90 and of the F-spin multiplet in Dy-Hf

The N = 90 isotones of Nd, Sm, Gd and Dy, with almost similar deformed level structure and associated with X (5) symmetry, form the isotonic multiplet in Z = 50?C66, N = 82?C104 quadrant. This is explained microscopically in terms of the Nilsson level diagram. Using the Dynamic Pairing-Plus-Quadrupole model of Kumar-Baranger, the quadrupole deformation and the occupancies of the neutrons and protons in these nuclei in the Nilsson orbits have been calculated, which support the formation of N = 88, 90 isotonic multiplets. The existence of the F-spin multiplets, with almost identical spectra, recognized in earlier works, in Z = 66?C82, N = 82?C104 quadrant, is also explained microscopically in our study.     

Detecting galactic cosmic ray transuranium nuclei in olivine crystals from meteorites

Results from the experimental search for and identification of tracks from the superheavy and transuranium nuclei of galactic cosmic rays in pallacite olivine crystals, conducted as part of project OLIMPIA [1], are presented. To date, 170 crystals from Marjalahti and Eagle Station pallacites have been processed and 6800 tracks corresponding to nuclei with charges Z > 55 have been found; 45 of these are from nuclei with charges of 88 < Z < 92 and three super-long ones were produced by nuclei with Z > 105. The charge of one of these nuclei is estimated in the first approximation as Z = 119(+10,?6). Our data confirm the hypothesis of islands of stability for natural trans-Fermi nuclei.     

A new mass formula and new neutron and proton magic numbers in light nuclei

This mass formula explains gross features of the binding energy curves for all the elements from Li to Bi. It has no shell effects incorporated. Comparisons of separation energies computed from this formula and measured masses show extra-stability at N=6 (Z=3?8), Z=6 (N=6?9), N=14 (Z=7?10), Z=14 (N=14?19), N=16 (Z=7?8), Z=16 (N=24?26), loss of magicity at N=8 (Z=4), N=20 (Z=12?15) and quenching of N=50, 82, 126, Z=50 near driplines. Z=82 magicity rises at N=104 after strong quenching near N=107.     

Shell structure and shapes of superheavy nuclei

Shell structure and shapes of superheavy nuclei are discussed. Both deformed and spherical nuclei are considered. Theoretical results obtained for even-even nuclei with the proton numberZ=82–120 and neutron numberN=126–190 are examined.     

Neutron separation energy for heavy and superheavy nuclei

The neutron separation energy is calculated within a macroscopic-microscopic approach for nuclei with proton and neutron numbers, Z=82?128 and N=126?190, respectively. The results are compared with existing experimental and other theoretical data.     

Atomic masses above146Gd derived from a shell model analysis of high spin states

From a shell model analysis of high-spin states in neutron deficient nuclei above¹⁴⁶Gd we have derived the ground state masses of theN=82 and 83 isotones of Eu, Tb, Dy, Ho, and Er. The results can be used to calculate the energies of aligned multiparticle yrast configurations. They also link ten α-decay chains to the nuclei with known masses, providing many new absolute mass values which are compared with predictions. An examination of the two-proton separation energies atN=82 shows an 0.5 MeV break in the nuclear mass surface atZ=64.     

Spontaneous fission of isomeric states of actinide nuclei

Spontaneous fission half-lives of K-isomeric states are calculated on the basis of microscopic- macroscopic method. The isomeric state is assumed to be a 2-quasiparticle excited state with high angular momentum.The calculations were performed for nuclei with 96 < Z < 110 and 144 < N < 158. It was shown that in the case of K-isomeric states (if they exist) the spontaneous fission half-life time may be comparable to the spontaneous fission half-life time of the ground state. Therefore it was suggested that in measurements of fission half-lives it may be very important to distinguish between both possible components (or more) of the fission decay.     

The effect of the valence nucleons off the shells with <Emphasis Type="Italic">Z</Emphasis> = 82 and <Emphasis Type="Italic">N</Emphasis> = 126 on rotational characteristics of actinide nuclei

Our earlier results obtained for moments of inertia (M) in the case of 54 rotational level bands built on the ground state of actinide nuclei are taken for further analysis. In the current paper, resulting dynamic rotational characteristics, such as a ₀, a ₁, s ₀ and the R _4/2 parameter, are studied from the standpoint of their dependence on the valence nucleon number product N _p N _n and on the variable P = N _p N _n /(N _p + N _n ). New features of the nuclei deformation phenomenon in the actinide area arise when their dynamic rotational characteristics, mentioned above, are plotted in such a way as shown in the current work. The method of analysis presented here makes it possible to reveal nuclei with valence nucleon numbers for which the nuclear interactions are notable and those in which they are inconspicuous. E. g. when N _p N _n < 200 and P < 6 the strength of nuclear interaction gradually decreases with the increase of these variables. The strength of the nuclear interaction does not change significantly for N _p N _n > 200 and P > 6 — the rotational characteristics stabilise. Moreover, it is possible to establish the P variable as representing the effective number of interactions of each valence nucleon with those of the other type.     

Magnetic moments of K isomers as indicators of octupole collectivity

The relation between the quadrupole-octupole deformation and the structure of high-K isomers in heavy even-even nuclei is studied through a reflection asymmetric deformed shell model including a BCS procedure with constant pairing interaction. Two-quasiparticle states with K ^?? = 4^?, 5^?, 6^?, 6⁺ and 7^? are considered in the region of actinide nuclei (U, Pu and Cm) and rare-earth nuclei (Nd, Sm and Gd). The behaviour of two-quasiparticle energies and magnetic dipole moments of these configurations is examined over a wide range in the plane of quadrupole and octupole deformations (?? ₂ and ?? ₃. In all considered actinide nuclei, the calculations show that there is pronounced sensitivity of the magnetic moments to the octupole deformation. In the rare-earth nuclei, the calculations for ^{154, 156}Gd show stronger sensitivity of the magnetic moment to the octupole deformation than in the other considered cases.     

Giant resonance in the total photoabsorption cross section of Z ≈ 90 nuclei

Total photoabsorption cross sections of ²³²Th, ²³⁵U, ²³⁸U and ²³⁹Pu have been measured in the giant resonance region by the absorption method. Measured cross sections were approximated by two Lorentz lines. Lorentz line parameters, integrated cross sections, deformation parameters and quadrupole moments are given. The analysis of the nuclear optical anisotropy evolution with the increase of Z shows that Z ≈ 90 nuclei seem to be transitional, similar to N ≈ 90 nuclei. A comparison of experimental cross sections with dynamic collective model calculations has been performed. The evidence that quadrupole photoabsorption occurs in the 20–25 MeV energy region is also presented.     

Ab initio calculation of double mass differences for near-magic nuclei

Double mass differences between nuclei with a magic number of protons (neutrons) and their neighbors differing from them by one or two protons (neutrons) are calculated within the semimicroscopic model proposed recently for the nuclear pairing problem. The main term in the effective nucleon interaction is calculated on the basis of the realistic Argonne nucleon-nucleon potential v₁₈. This term is supplemented with a small phenomenological term involving one universal parameter common to protons and neutrons. The double mass differences are calculated for the proton neighbors of the Z = 82, 50, 28, and 20 lead, tin, nickel, and calcium isotopic chains and for the neutron neighbors of the N = 126, 82, 50, and 20 isotonic chains. The corrections to the model that are induced by the contribution of low-lying surface vibrations (phonons) are discussed.     

Deformed Hartree-Fock calculation of proton-rich nuclei

We perform Hartree-Fock+BCS calculations for even-even nuclei with 2 ≤ Z ≤ 82 and N ranging from outside the proton drip line to the experimental frontier on the neutron-rich side. The ground state solutions are obtained for 737 nuclei, together with shape-coexistence solutions for 480 nuclei. Our method features the Cartesian-mesh representation of single-particle wavefunctions, which is advantageous in treating nucleon skins and exotic shapes. The results are compared with those of the finite-range droplet model of Møller et al. as well as the experimental values.