Octupole deformation in the actinide region

Properties of nuclei exhibiting the features of intrinsic reflection asymmetry, identified and studied at ISOLDE and ISOLDE PSB, are reviewed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Self-consistent calculation of the quadrupole-octupole deformation energy surface of 222Ra

The Hartree-Fock + BCS quadrupole-octupole deformation energy surface of ²²²Ra, calculated with the Skyrme SIII interaction, presents a minimum for a non-zero value of the octupole moment. Our results suggest the existence of a quadrupole coupling which may account for the observed differences between the moments of inertia of the positive- and negative-parity bands.     

Hyperdeformation and clusterization in the actinide region

The ²³³U(d,pf)²³⁴U, and the ²³⁵U(d,pf)²³⁶U reactions have been studied with high energy resolution. The observed fission resonances were described as members of rotational bands with rotational parameters characteristic of hyperdeformed nuclear shapes. Information on the K values of the bands and for the J values of the band members has been obtained from fission fragment angular distribution measurements. The level density of the most strongly excited states has been compared to the prediction of the back-shifted Fermi-gas formula and the energy of the ground state in the third minimum has been estimated for ²³⁴U. The fission fragment mass distribution of the hyperdeformed states in ²³⁶U has also been measured. The width of the mass distribution, coincident with the hyperdeformed bands, is significantly smaller than the ones obtained in coincidence with background regions below and above the resonances, which suggests a pear-shaped di-nuclear configuration of ²³⁶U in the third well of the potential barrier.     

Hyperdeformation and clustering in the actinide region

The excitation energy spectrum of fission resonances has been measured with high energy resolution using the ²³⁵U(d,pf) reaction in order to study hyperdeformed (HD) rotational bands and HD nuclear shapes. The moments of inertia of the rotational bands and the energy of the ground state in the third minimum were determined. Another signature of these highly deformed states, their enhanced α decay, was also observed. By studying cold or compact fission in the ²³²Th(n,f) reaction around HD resonances, we obtained data for heavy clustering.     

New modified oscillator potential for nuclei in the actinide region

A modified oscillator potential with a new form of correction term giving the proper value of the dynamical moment of inertia is investigated. A set of parametersκ andμ for nuclei in the actinide region is given. The single particle levels around the Fermi surface obtained here are close to those calculated with the Nilsson potential with the traditional correction term.     

Effect of elastoplastic deformation on the static friction force

A study was made of elastoplastic deformation In surface layers caused by normal and tangential forces. A definite relationship is shown to exist between the external friction force and elastoplastic deformation. Maximum elastoplastic deformation arises in the contact zone when static friction is replaced by moving friction. The maximum elastoplastic deformation corresponds to the static friction force.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 34–37, September, 1969.     

Precision measurements of x-ray energies,natural widths and intensities in the actinide region

A Dumond-type curved crystal spectrometer has been used to measureK x-ray energies, natural widths and relative intensities for the eleven actinides from₈₈Ra to₉₈Cf. The results are compared to the most recent theoretical predictions.     

The determination of hexadecapole deformation parameters in actinide nuclei and their variation near the nuclear surface

By computing self consistently the nuclear density of²³⁸U with the Skyrme SIII effective force, the hexadecapole deformation parameter has been found to vary considerably in the nuclear surface. This suggests an explanation for some discrepancies observed betweenβ ₄ parameters estimated from different inelastic scattering experiments.     

Jumpwise deformation of polymethyl methacrylate in the microplasticity region

The deformation rate with a step of 325 nm has been measured under uniaxial compression at the initial stage of creep and shape recovery of a polymethyl methacrylate (PMMA) sample after unloading. The effect of low γ-ray doses and magnetic fields on the deformation has been studied. It has been shown that a weak pre-exposure of the PMMA sample structure to radiation and magnetic fields can cause a slight hardening in the microplasticity region. The deformation jump sizes have been determined on micro- and nanoscales. The effect of irradiation and magnetic fields manifests itself as redistributed contributions of various jumps to the deformation.     

Possible evidence for static octupole deformation in128,129Ba

It is demonstrated that recent experimental results on high spin states of^128,129Ba offer substantial new evidence for static octupole deformation in these nuclei.     

Photofission of actinide nuclei in the nucleon-resonance region: First photonuclear experiment at the Siberia-2 storage ring

Results of an experiment performed to study ²³⁸U photofission with the aid of the initial section of the GAMMA channel of the Siberia-2 storage ring at the Kurchatov Institute are presented. These results are predominantly of a methodological value, because a photonuclear experiment was conducted for the first time in this channel. However, the data obtained in this way allowed us to evaluate an upper limit on the probability of the fast fission (fragmentation) of ²³⁸U nuclei that was induced by photons of energy up to 2.5 GeV. This is pertinent to the problem of the deviations of the total photoabsorption cross sections for actinide nuclei from a “universal curve.”     

Stress relaxation in the region of microplastic deformation of polycrystals

Stress relaxation equations are derived to predict the relaxation capacity of a material on the basis of studies of microplastic deformation under static loading. The approach was checked experimentally on spring steels LANKMts, ÉI702, ÉP637, and 50KhFA.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 37–41, July, 1987.     

Magnetism of actinide compounds

We review the physical properties of actinide compounds, with particular emphasis on their magnetic characteristics. Because of the complexity of these materials, mainly the simplest compounds are treated, some of which have properties that can be theoretically explained.     

The static generalized susceptibility for a ferromagnet in the critical region

A method of calculating the static generalized susceptibility for the critical region in the constant coupling approximation has been formulated and applied to ferromagnets above the Curie point, leading to an anisotropic susceptibility.     

A new static calculation of the streamer region for long spark gaps

Different electrostatic approximations have been proposed to calculate the streamer region without going in deep details of the behavior of density of particles under the effect of high electric fields; this kind of approximations have been used in numerical calculations of long spark gaps and lightning attachment. The simplifications of the streamer region are achieved by considering it to be a geometrical region with a constant geometrical shape. Different geometrical shapes have been used, such as cones or several parallel filaments. Afterward, to simplify the procedures, the streamer region was approximated by two constants, one denoted K_Q, called the geometrical constant and in other cases K named as geometrical factor.However, when a voltage that varies with time is applied to an arrangement of electrodes (high voltage and grounded electrodes), the background electric field will change with time. Thus, if the background electric field is modified, the streamer zone could cover a larger or smaller area.With the aim of reducing the number of assumptions required in the calculation of long gap discharges, a new electrostatic model to calculate the streamer region is presented. This model considers a variable streamer zone that changes with the electric field variations. The three-dimensional region that fulfills the minimum electric field to sustain a streamer is identified for each time step, and the charge accumulated in that region is then calculated. The only parameter that is being used in the calculation is the minimum electric field necessary for the propagation of streamers.     

Microplastic deformation of polycrystalline and submicrocrystalline titanium during static and cyclic loading

A study is made of the laws governing the accumulation of microplastic strain during the static and cyclic loading of polycrystalline and submicrocrystalline titanium. It is shown that a change from the polycrystalline structure to the submicrocrystalline structure does not change the character of development of microplastic strain for either type of loading, but it does increase fatigue strength and fatigue limit. A correlation between the fatigue strength based on 10⁶ cycles and the macroscopic elastic limit was found to exist for both types of loading. Siberian Physico-Technical Institute (at Tomsk University), Institute of the Physics of Strength and Materials Science (in the Siberian Division of the Russian Academy of Sciences), and the Institute of the Physics of Promising Materials (at Ufa State University of Aeronautical Engineering). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 41, No. 12, pp. 20–25, December, 1998.     

The effect of coarse non-deformable particles on the deformation and static recrystallization of aluminium alloys

The phenomenon of particle-stimulated nucleation (PSN) during recrystallization of commercial aluminium alloys has been widely investigated both from a ;scientific viewpoint and from the industrial perspective. The technological impact of this phenomenon is the finding that, depending upon the thermomechanical processing conditions, the occurrence of PSN may strengthen or weaken the deformation texture during recrystallization, which may or may not be desirable ;for a specific application of the final product. From a scientific standpoint, the mechanics of formation of localized deformation zones in the vicinity of the hard particles and the development of deformation substructures within the ;deformation zone that eventually turn into a recrystallized nucleus are still not ;completely understood. This paper describes the application of a coupled finite-element–Monte Carlo technique to study the phenomenon of PSN during recrystallization of aluminium and the subsequent growth of the nuclei. The deformation and recrystallization textures arising from initial microstructures with and without hard particles are compared to elucidate the particle effect on texture. The simulations have been applied to single crystals, bicrystals and a tricrystal of aluminium of specific crystallographic orientations with and without the hard particles at specific locations such as the grain interior, grain boundary and triple line. The simulation results are compared with existing experimental data on the deformation and recrystallization of particle-containing aluminium alloys.     

Absorption spectra of actinide compounds

From the energy levels of the gaseous ions Ac⁺⁺, Th⁺⁺⁺, and Th⁺⁺, it can safely be extrapolated that the ground electron configuration of all actinide ions with ionic charges at least + 3 contains only 5f-electrons outside the emanation shells. This is further supported by the 5fⁿ → 5f^n-16d transitions observed in Pa(IV), U(III), Np(III) (though their wave numbers are too high to be measured in U(IV) and Np(IV)). The configuration f² has a very characteristic distribution of energy levels between ³H₄ and ³P₂ with ¹S₀ as much higher, isolated level. The absorption spectra of U(IV) complexes and of PuF₆ suggest interelectronic repulsion parameters ～60 per cent of the values in the corresponding lanthanides, while the Landé factors are about twice as large. This would also explain the recent measurements of Cm(III) complexes, compared to Gd(III). The larger average radius of the 5f-shell causes larger perturbation effects from the ligands than in the lanthanides. The J-values will therefore be distributed between several adjacent, observed energy levels without making the general treatment of the fⁿ-configurations impossible. The variation with oxidation numbers in isoelectronic series are discussed, e.g. U(III) and Np(IV); Pu(III) and AmF₄; and Am(III) and CmF₄. Band positions are predicted in Bk(III) and BkF₄. Finally, the chemical properties of the actinide elements are discussed, and it is emphasized that no necessary connections exist between the presence of f-electrons and constant trivalency.     

Volume compressibilities of actinide materials

Abstract

Using an X-ray diffractometer of the Guinier type the bulk moduli B,₀ of NpAs (NaCl structure) and of NpSn₃ (cubic AuCu₃ structure) were measured at room temperature. We find B₀ = (75.3±5.0)GPa, B₀' = (3.7 ± 1.0) for NpAs and B₀ = (72.2 ± 11.6) GPa, B₀' = (5.6 ± 4.1) for NpSn₃. Compared to the results on NpA1₂ and NpOs₂ the B₀ value for NpSn₃ is surprisingly small and supports the interpretation of high pressure Mössbauer data that this intermetallic behaves like a localized 5f electron system. In addition, we report on experimental modifications of the diffractometer which make compressibility measurements possible also at low (down to ～ 10 K) temperatures.