Fission fragment mass yields of Th to Rf even-even nuclei

Fission properties of the actinide nuclei are deduced from theoretical analysis. We investigate potential energy surfaces and fission barriers and predict the fission fragment mass yields of actinide isotopes. The results are compared with experimental data where available. The calculations were performed in the macroscopic-microscopic approximation with the Lublin-Strasbourg Drop (LSD) for the macroscopic part, and the microscopic energy corrections were evaluated in the Yukawa-folded potential. The Fourier nuclear shape parametrization is used to describe the nuclear shape, including the non-axial degree of freedom. The fission fragment mass yields of the nuclei considered are evaluated within a 3D collective model using the Born-Oppenheimer approximation.     

On the properties of the extended ground rotational bands in actinide even-even nuclei

The energies of the yrast levels extending up to I = 28 in even-even actinide nuclei were analyzed in terms of an angular velocity expansion E_rot(I) = ∑_i=1ⁿα_iω_I²ⁱ with n = 2?7 to test the application of this expansion to high spin. A strong ω²-dependence is observed for the Variable Moment of Inertia model (VMI) with two parameters α_i(ω²), particularly at the higher spins. There is a marked difference in the ω²-dependence, of these parameters between the N = 142 and other nuclei studied in this region to indicate structure effects are present at the higher spin.     

Fission barriers of preactinide nuclei from electrofission experiments

Absolute electrofission cross sections for ^182,184,186W, ^natPt, and ²⁰⁹Bi have been measured using solid-state track detectors and parallel-plate avalanche counters for the detection of the fission fragments. The measured cross sections — together with others known from literature — have been analyzed within an extended statistical model to deduce fission barriers and compared with theoretical calculations. From the derived barrier height for platinum, it is concluded that the pairing strength G most likely does not change with deformation (G = const). All experimental fission barriers agree very well with theoretical predictions for G = const.     

Fission barriers of Pb nuclei at high angular momentum

Fission and evaporation residue excitation functions have been measured after the nuclei ^{192, 195, 198, 200}Pb were formed by the fusion of ^{28, 30}Si with ^{164, 167, 170}Er. The fission probabilities extracted were fitted using the rotating liquid drop/statistical model codes ORNL ALICE and MBII. The range of values of the mass asymmetry, $\text{(N?Z)}\text{A}$, of the fissioning systems allows some restrictions to be placed on the value of the surface asymmetry parameter K_s, used in the liquid drop model, despite the many uncertainties and approximations in the data analysis.     

Fission barriers of super-heavy nuclei produced in cold-fusion reactions

Excitation functions of super-heavy evaporation residues formed in cold-fusion reactions were analyzed with the aim of getting information on the fission barrier height of these nuclei. The method uses the location of the maximum of 1n and 2n excitation functions. The results obtained on nuclei from Z = 104 to 112 are compared to three theoretical predictions.PACS: 25.70.Jj Fusion and fusion-fission reactions - 24.75. + i General properties of fission     

Fission barriers and other characteristics of nuclei from the uranium region

Fission barriers in nuclei belonging to the uranium region and their other characteristics are calculated on the basis of the FaNDF⁰ energy density functional. In particular, the neutron-separation energies S _n and S _2n, the proton-separation energies S _p, and the beta-transition energiesQ _β are calculated for uranium, neptunium, and plutonium isotopes. In addition, the deformation energies and parameters of these nuclei are presented along with their radii. A comparison with the predictions of the Skyrme–Hartree–Fock method implemented with several versions of the Skyrme energy density functionals is performed. The role of the octupole deformation β ₃ is studied for the ²³⁸U nucleus. It is shown that this deformation does not have any significant effect on the first-barrier height B ⁽¹⁾ _f or ground-state properties. At the same time, the second-barrier height B(2) f decreases by a factor of about two upon taking into account β ₃. A phase transition at A ~ 260 is found for the three isotopic chains being considered: this point is a bifurcation point at which B ⁽¹⁾ _f (A) forks into two curves. Of these, the curve B ⁽²⁾ _f (A) splits from it, prolonging the former curve for B ⁽¹⁾ _f (A) almost continuously, whereas the curve for B ⁽¹⁾ _f (A) itself goes down sharply.     

Subthreshold photofission of even-even nuclei

Within quantum-mechanical fission theory, the angular distributions of fragments originating from the subthreshold photofission of the even-even nuclei ²³²Th, ²³⁴U, ²³⁶U, ²³⁸U, ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu are analyzed for photon energies below 7 MeV. Special features of various fission channels are assessed under the assumption that the fission barrier has a two-humped shape. It is shown that the maximum value of the relative orbital angular momentum L _m of fission fragments can be found upon taking into account deviations from the predictions of A. Bohr’s formula for the angular distributions of fission fragments. The result is L _m ≈ 30. The existence of an “isomeric shelf” for the angular distributions of fragments from ²³⁶U and ²³⁸U photofission in the low-energy region is confirmed.     

Descriptive study of the even-even actinide nuclei ~(230-234)Th isotopes using IBM-1

The nuclear structure of the actinide even–even thorium isotopes from A=230-234 have been investigated within the framework of the Interacting Boson Model(IBM-1). Predictions are given for the excited state energies for the ground state, β and γ-bands, the transition probabilities between these states, the rotational moment of inertia, and the energy staggering in the γ-band energies. The results of these calculations are compared with the experimental data on these isotopes.     

An extended phonon projection model for even-even nuclei

An extension of the projection model of Lipas et al. is presented. This extended phonon projection model (EPM) includes diagonalization in a projected-state basis and the extension of the laboratory hamiltonian to include anharmonic terms. The oriented system is used in generating the model space. A comparison of the EPM predictions with those of the six-parameter 1BA-1 model is made for ^148–152Sm.     

Criteria for comparison of bands in even-even nuclei

A cluster model gives a satisfactory reproduction of normal deformed (ND) ground state bands in a wide range of even-even nuclei. We show here that the fractional change of the transition energies in two bands is closely related to the fractional change in the corresponding reduced masses. We compare our predictions to data on ground state ND bands for a series of light rare-earth and actinide isotopes.     

Binding energies of even-even superheavy nuclei

The structure of the even-even superheavy nuclei with the proton number Z=98–110 is studied using the self-consistent relativistic mean-field theory. The calculated binding energies are in good agreement with the available experimental ones. An upper limit and a lower limit on the binding energies are set by the calculations. This is useful for future calculations of properties of superheavy nuclei and for the experimental synthesis of superheavy nuclei. The energy surface of some relevant superheavy nuclei is also given and it confirms the correctness of the calculations.     

On symmetry energy of even-even nuclei

A density dependent contact force whose parameters are derived from the requirements of translational invariance and gauge invariance is applied to spectroscopic studies in²⁰⁸Pb. It is shown that spectroscopic studies of states of natural parity and of electric multipole transitions yield no physically significant, additional information on force parameters compared to the translational invariance subsidiary condition.     

Excited states of deformable even-even atomic nuclei

A method of calculating the collective excited states of even-even atomic nuclei is proposed. A formula depending on three parameters appropriate for calculating the energy ratios of the excited states of deformed and spherical nuclei as well as those in the intermediate region is obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 19–24, November, 1972.     

Excited collective states of heavy even-even nuclei

Quadrupole-type collective excitations of even-even nuclei are analyzed. In this analysis, transverse γ vibrations of the nuclear surface are taken into account effectively, while longitudinal beta vibrations remain free. A potential energy of the exponential form is used for free surface longitudinal beta vibrations. The behavior of the energy levels of excited states in the ground-state, β, and γ bands of heavy nuclei is studied, and the predictive potential of the model used is demonstrated for transfermium nuclei.     

Detailed spectroscopy of superdeformed actinide nuclei

Progress in the experimental techniques used to investigate superdeformed fission isomers in the actinides allowed for detailed spectroscopic results of collective properties as well as for the identification of the rotational structure of multiphonon vibrational excitations. A novel approach could be established to determine the depth of the second potential well.