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.     

The new isotope 270110 and its decay products 266Hs and 262Sg

The even-even nucleus ²⁷⁰110 was synthesized using the reaction ⁶⁴Ni + ²⁰⁷Pb. A total of eight α-decay chains was measured during an irradiation time of seven days. Decay data were obtained for the ground-state and a high-spin K isomer. The new nuclei ²⁶⁶Hs and ²⁶²Sg were identified as daughter products after α-decay. Spontaneous fission of ²⁶²Sg terminates the decay chain. The measured data are in agreement with calculations using the macroscopic-microscopic model and with self-consistent HFB calculations with Skyrme-Sly4 interaction. Received: 27 November 2000 / Accepted: 16 January 2001     

Calculated properties of superheavy nuclei

Ground-state properties of the heaviest nuclei are analyzed within a macroscopic-microscopic approach. The main attention is paid to such properties as deformation, deformation energy, energy of the first rotational state 2⁺ of a nucleus, and the branching ratio of α decay to this 2⁺ state with respect to the decay to the ground state 0⁺. The analysis concerns the problem of experimental confirmation of theoretically predicted deformed shapes of superheavy nuclei situated in the region around the nucleus ²⁷⁰Hs. A large region of even-even nuclei with proton, Z=82–128, and neutron, N=126–190, numbers is considered.     

Calculated masses of heaviest nuclei

Masses of heaviest nuclei are calculated within a macroscopic-microscopic approach. Even-even, odd-A, and odd-odd nuclides are considered. A large region of nuclei with proton and neutron numbers of Z=82–128 and N=126–192, respectively, is analyzed. The results are compared with those of other macroscopic-microscopic and of recent microscopic Hartree-Fock-BCS calculations. Alpha-decay energies are also given.     

Mass and excited levels of the neutron-rich nuclei 73Zn and 74Zn studied with the 76Ge(14C, 17O) and (14C, 16O) reactions

The ⁷⁶Ge(¹⁴C, ^{16, 17}O)^{74, 73}Zn reactions have been studied at 72 MeV bombarding energy. The mass excesses of ⁷³Zn and ⁷⁴Zn were determined to be ?65.41 ± 0.04 and ?65.62 ± 0.04 MeV, respectively. In addition, previously unknown excited levels were identified in both nuclei. The structure of ⁷³Zn is discussed in terms of HFB calculations.     

Mössbauer study of Zn2+ and Sn4+ additives in Nickel ferrites

The Mössbauer study of Fe⁵⁷ in polycrystalline solid solutions of Ni_{1 + x ? y}Zn_ySn_xFe_{2 ? 2x}O₄ (y = 0.1, 0.3, 0.5 and x = 0.1 to 0.5 with x varying in steps of 0.1) has been made. The present work has been aimed at investigating the variation of isomer shift, nuclear magnetic field at Fe⁵⁷ nuclei and ionic distribution at tetrahedral and octahedral sites when the concentration of Zn²⁺ and Sn²⁺ ions is successively increased in nickel ferrites. The ionic distribution in samples having low tin concentration has been explained on the basis of Neel's molecular field model whereas the ionic distribution of samples having high tin and zinc concentration has been explained on the basis of formation of isolated superparamagnetic clusters at the octahedral site. It has been inferred that a larger substitution of zinc and tin ions enhances relaxation effects.     

Hartree-Fock and Hartree-Bogolyubov calculations inp shell nuclei

Hartree-Fock (HF) and Hartree-Fock-Bogolyubov (HFB) calculations have been performed for the 1p shell nuclei. Nuclear deformations are assumed to be at most axially symmetric. The HFB transformation is restricted to allow forp-p andn-n pairing only.Volkov's force, a soft-core, two-body interaction of semi-realistic nature, is used which does not produce any single-particle spin-orbit splittings. Coulomb force and the usual correction for centre-of-mass motion are taken into account. The calculations are carried out in a single-particle basis including all states up to principle oscillator quantum numberN=3 (in some cases,N=4). Binding energies, rms radii, density distributions, and quadrupole moments are calculated and found to be in reasonable agreement with experiment. Large Hartree-Fock energy gaps are obtained. They prevent the pairing correlations considered from becoming effective in an HFB approach and from changing the HF ground-state properties appreciably. In non-selfconjugate nuclei, the Pauli principle, rather than the Coulomb interaction, yields large differences between the charge and mass distributions. A theorem on selfconsistent symmetries is proved. The coefficients of the HFB transformation turn out to be real, if time-reversal and angular momentum projection flip are selfconsistent symmetries.     

Effects of shell correction on α decay properties

The shell correction effects on the α decay properties of heavy and superheavy nuclei have been studied in a macroscopic-microscopic manner. The macroscopic part is constructed from the generalized liquid drop model(GLDM), whereas the microscopic part, namely, the shell correction energy, brings about certain effects on the potential barriers and half-lives under a WKB approximation, which is emphasized in this work. The results show that the shell effects play a significant role in the estimation of the α decay half-lives within the actinide region.Predictions of the α decay half-lives are then generated for superheavy nuclei, which will provide useful information for future experiments.     

Collective bands in even mass Sn isotopes

Positive parity bands in ^{112, 114, 116, 118}Sn have been excited up to levels with spin and parity J^π = 12⁺ using Cd(α, 2nγ)Sn reactions. The experiments consisted of γ-ray excitation function, γ-γ coincidence, lifetime, γ-ray angular distribution, γ-ray linear polarization and conversion electron measurements. The observed bands show strong resemblances with ground-state bands of transitional nuclei in this mass region. It is pointed out that the J^π = 0⁺ band-heads originate from 2p-2h excitations in the Z = 50 proton shell. The excitation energies of the band-heads are calculated by means of the macroscopic-microscopic renormalization method. Pair correlations between the 2h and 2p configurations are included separately in a phenomenological way by taking into account the pairing energies of the Cd and Te ground states with respect to the Sn ground state.     

Microscopic analysis of the fission barriers in <Superscript>256</Superscript>Fm and <Superscript>258</Superscript>Fm

The fission barriers of ²⁵⁶Fm and ²⁵⁸Fm have been analyzed in the HFB theory. The potential energy and the effective inertia parameter have been calculated in the two-dimensional deformation space of quadrupole and octupole moments. Fission paths for various octupole moments of the exit point from the fission barrier have been determined. The half-life along each path has been calculated. The shortest half-lives have been obtained for the paths with reflection symmetric shapes of nuclei in both the considered isotopes.     

Consistent empirical physical formulas for potential energy curves of 38–66Ti isotopes by using neural networks

Nuclear shape transition has been actively studied in the past decade. In particular, the understanding of this phenomenon from a microscopic point of view is of great importance. Because of this reason, many works have been employed to investigate shape phase transition in nuclei within the relativistic and nonrelativistic mean field models by examining potential energy curves (PECs). In this paper, by using layered feed-forward neural networks (LFNNs), we have constructed consistent empirical physical formulas (EPFs) for the PECs of ^38–66Ti calculated by the Hartree-Fock-Bogoliubov (HFB) method with SLy4 Skyrme forces. It has been seen that the PECs obtained by neural network method are compatible with those of HFB calculations.     

Non-axial shapes in spontaneous fission of superheavy nuclei

We test the importance of non-axial nuclear shapes in spontaneous fission of heavy and superheavy even-even nuclei from the region around a hypothetical doubly magic nucleus ²⁹⁸114. Fission half-lives are calculated by finding dynamical fission paths as dictated by the least WKB action principle with the macroscopic-microscopic energy and the cranking inertial parameters. Results show that the effects of non-axial shapes on the fission process are weakened by the inertia tensor and become important only for the heaviest elements with Z ⩾ 120.     

High-accuracy mass determination of unstable cesium and barium isotopes

Direct mass measurements of short-lived Cs and Ba isotopes have been performed with the tandem Penning trap mass spectrometer ISOLTRAP installed at the on-line isotope separator ISOLDE at CERN. Typically, a mass resolving power of 600 000 and an accuracy of δm ≈ 13 keV have been obtained. The masses of ^123,124,126Ba and ^122mCs were measured for the first time. A least-squares adjustment has been performed and the experimental masses are compared with theoretical ones, particularly in the frame of a macroscopic-microscopic model.     

Mössbauer study of 119Sn hyperfine interactions in the KTi1−x SnxOPO4 system

The first Mössbauer study of hyperfine interactions of ¹¹⁹Sn nuclei in the complex ferroelectric oxides KTi_1?x Sn_xOPO₄ is reported. A one-to-one correspondence between the hyperfine interaction parameters and tin atom arrangement in cis and trans positions of the structure has been established. The electric-field gradient at ¹¹⁹Sn nuclei is shown to be dominated by the contribution of valence electrons in the hybridized p and d orbitals. A linear correlation between the quadrupole displacement of the spectrum components and the average Sn-O distances has been revealed. The Mössbauer line shift data were used to estimate the number of valence s electrons of Sn⁴⁺ ions occupying the cis and trans positions throughout the x range covered.     

Calculations of the β-decay half-lives of neutron-deficient nuclei

In this work,β~+/EC decays of some medium-mass nuclei are investigated within the extended quasiparticle random-phase approximation(QRPA),where neutron-neutron,proton-proton and neutron-proton(np) pairing correlations are taken into consideration in the specialized Hartree-Fock-Bogoliubov(HFB) transformation.In addition to the pairing interaction,the Br¨uckner G-matrix obtained with the charge-dependent Bonn nucleon-nucleon force is used for the residual particle-particle and particle-hole interactions.Calculations are performed for even-even proton-rich isotopes ranging from Z =24 to Z =34.It is found that the np pairing interaction plays a significant role inβ-decay for some nuclei far from stability.Compared with other theoretical calculations,our calculations show good agreement with the available experimental data.Predictions of β-decay half-lives for some very neutron-deficient nuclei are made for reference.     

New isomeric states in 152,154,156Nd produced by spontaneous fission of 252Cf

Isomeric states have been observed in fission-fragments produced by spontaneous fission of ²⁵²Cf. These states are found in neutron rich nuclei of different structure and deformations. About 50 isomeric nuclei have been observed using coincidences between γ-rays identified in EUROGAM II and fission fragments detected in photovoltaic cells (SAPhIR). Lifetimes in the range from 20 ns to 2μs have been measured. Presented calculations based on HFB +D1S force on new measured isomeric states in the ^152,154,156Nd show evidence for K-isomers. Received: 3 November 1997 / Revised version: 15 December 1997     

N=28丰中子核的形变和形状共存研究

利用同位旋依赖的尼尔逊势,在宏观-微观理论框架下,计算了幻数N=28同中子链上原子核的性质,研究了N=28同中子链上原子核的形变和形状共存现象. 研究结果表明,N=28这个幻数在Na,Mg, Al同位素链上有着强的形状共存现象. 此外,计算表明⁴²Si的基态为扁椭球,同时在Si同位素链上的形状共存现象相对较弱. 关键词： 同位旋 幻数 形变 形状共存     

Attenuation of cosmic ray heavy nuclei fluxes in the upper atmosphere by fragmentation

Two plastic stacks containing cellulose nitrate as detector material were flown several times with balloons at 40 g cm^?2 for a total time of 25 hours. From the tracks of 920 heavy nuclei the vertical intensities of the particles of four charge groups (6 ? Z ? 9, 10 ? Z ? 14, 15 ? Z ? 19, 20 ? Z ? 28) have been derived for atmospheric depths from 40 – 100 g cm^?2. Combining these intensities with other results obtained with emulsions and in counter measurements, the fragmentation probabilities in air have been determined by comparison with the primary spectra.     

Possible candidate nuclei for chirality-parity quartet bands

The potential energy surfaces of the even-even~(68-92)Se,~(112-150)Ba,and~(208-230)Ra isotopes are calculated using the macroscopic-microscopic method in a multidimensional space{α_(λ,μ)}including quadrupole(λ=2,μ=0,2)and octupole(λ=3,μ=0,1,2,3)degrees of freedom.The calculated results show that the even-even isotopes~(92)Se,~(112,114,144-150)Ba and~(220-228)Ra can exhibit the coexistence of triaxial and octupole deformations,thereby leading to simultaneous chiral and reflected symmetry breaking.Therefore,chirality-parity quartet bands are expected in these and their neighboring odd-A/odd-odd nuclei.