Light Actinides Research Articles

Total kinetic, excitation energy and neutron multiplicity distribution of californium isotopes

The mean total kinetic energy as a function of fission fragments, <TKE>(A), is calculated for neutron-induced fission of 247,249,251,253,255Cf, as well as for spontaneous fission of 248,250,252,254Cf using the scission point model. A comparative analysis is performed between the calculated results and existing experimental data. Investigation into the behavior of <TKE>(A) is conducted, particularly focusing on intermediate and heavy actinides. While nuclear and Coulomb energy evaluations suffice for estimating <TKE> values in light actinides, this approximation proves inadequate for evaluating TKE values for intermediate and heavy actinides. Additionally, an evaluation is made of the total excitation energy as a function of fission fragments, <TXE>(A), concerning spontaneous fission in 247−254Cf. It is found that TXE values sharply increase near the symmetric region across all isotopes and exhibit a gradual increase in heavy fission fragments. Furthermore, an exploration of the total neutron multiplicity as a function of fission fragments, νT(A), is conducted for 252Cf fission using two methods. The νT(A) results obtained through these methods are compared with experimental data, and νT(A) is estimated for unmeasured californium isotopes. The average neutron emission per fission event, ν¯(Ai), is then calculated for spontaneous fission of 251Cf and 253Cf, yielding values of 3.46 and 3.59, respectively.

Axially symmetric quadrupole-octupole incorporating sextic potential

We present an extended application of the analytic quadrupole octupole axially symmetric model, originally employed to study the octupole deformation and vibrations in light actinides using an infinite well potential (IW). In this work, we extend the model's applicability to a broader range of nuclei exhibiting octupole deformation by incorporating a sextic potential instead of the Davidson potential. Similarly to conventional models, such as AQOA-IW (for infinite square potential) and AQOA-D (for the Davidson potential), our proposed model is referred to as AQOA-S. By employing the sextic potential, phenomenologically represented as v(β˜)=a1β˜2+a2β˜4+a3β˜6, we can derive analytical expressions for the energy spectra and transition rates (B(E1), B(E2), B(E3)). The energy spectra of the model are essentially governed by two critical parameters: ϕ0, indicating the balance between octupole and quadrupole strain, and α, a key factor in adjusting the shape and behavior of the spectra through the sextic potential. In terms of applications, the study encompasses five isotopes, namely 222−226Ra and 224,226Th. Significantly, our model demonstrates remarkable agreement with the corresponding experimental data, particularly for the recently determined B(EL) transition rates of 224Ra, surpassing the performance of the model that employs the Davidson potential. The stability of the octupole deformation in 224Ra adds particular significance to these findings.

Microscopic formulation of the interacting boson model for reflection asymmetric nuclei

Reflection asymmetric, octupole shapes in nuclei are a prominent aspect of nuclear structure, and have been recurrently studied over the decades. Recent experiments using radioactive-ion beams have provided evidence for stable octupole shapes. A variety of nuclear models have been employed for the related theoretical analyses. We review recent studies on the nuclear octupole shapes and collective excitations within the interacting boson model. A special focus is placed on the microscopic formulation of this model by using the mean-field method that is based on the framework of nuclear density functional theory. As an illustrative example, a stable octupole deformation, and a shape phase transition as a function of nucleon number that involves both quadrupole and octupole degrees of freedom are shown to occur in light actinides. Systematic spectroscopic studies indicate enhancement of the octupole collectivity in a wide mass region. Couplings between the octupole and additional degrees of freedom are incorporated in a microscopic manner in the boson system, and shown to play a crucial role in the description of the related intriguing nuclear structure phenomena such as the shape coexistence.

Applications of a dual-column technique in actinide separations

Selective separation of an individual actinide of interest from other actinides and accompanying lanthanides is a challenging task in radiochemistry and radioanalytical chemistry. This paper illustrates a dual column technique (i.e., stacked columns of two appropriate resins) to separate an individual actinide of interest, where the selection of two resins and a common effluent running through the stacked columns are key parameters in design of an appropriate dual column. This paper describes the dual column design and practice with two examples, one for a heavy actinide 249Bk and the other for a light actinide 230U. In the former case, stacked columns of anion exchange (AX) resin and LN resin replaced the traditional CX-AHIB method used at Oak Ridge National Laboratory for 60 years. In the latter case, an elution process with an AX column followed with a stacked column of AX resin and a DGA resin was applied, instead of traditional methods, e.g., PUREX or U-TEVA methods. Application results of the dual column method to the two example actinides are displayed, while the considerations in method design and the required conditions are discussed.

Structure of Mass-Yield Distributions of 232Th Photofission Product by Bremsstrahlung at Energy 17.5 MeV

Relevance. One of the most promising areas for studying the fission process is to investigate its features under the action of photon radiation, since the interaction of gamma quanta with the nucleus is completely electromagnetic with well-known characteristics. Information on the yields of 232Th nuclear photofission products is of particular interest from the standpoint of experimental and theoretical studies. The nucleus of this element is located on the border between pre-actinides and light actinides. Purpose. The purpose of this study is to experimentally investigate the structure of the mass distribution of yields of 232Th photofission products at a bremsstrahlung energy of 17.5 MeV (energy close to the threshold of the first-chance fission, where experimental data are not available). Methods. 232Th photofission response was simulated on the electron accelerator of the Institute of Electron Physics NAS of Ukraine – M-30 microtron. The bremsstrahlung spectrum was modelled for the case of electron interaction (E=17.5 MeV) with a tantalum converter (1 mm) using the GEANT4 code 10.7. Yields of 232Th photofission products were measured by gamma-ray spectrometry. The yields of 232Th photofission products were modelled using the GEF 2020 / 1.1 and Talys 1.95 codes. Results. The value of cumulative yields of 23 products (85mKr, 88Kr, 88Rb, 89Rb, 91Sr, 92Sr, 94Y, 95Zr, 97Nb, 99Mo, 101Tc, 131I, 132Te, 133I, 134Te, 135I, 138Cs, 139Ba, 140Ba, 141Ce, 142La, 143Ce, 146Ce) belonging to 22 isobaric mass chains (light: 85; 88; 89; 91; 92; 94; 95; 97; 99; 101, heavy: 131; 132; 133; 134; 135; 138; 139; 140; 141 ; 142; 143; 146 fragments) of the 232Th photofission was measured at a maximum bremsstrahlung energy of 17.5 MeV (average excitation energy ~ 11.3 MeV). The resulting mass distribution of heavy fragments indicates the presence of increased yields of products localized around mass 133-134, 138-139, and 143-144, which is associated with the influence of such a nuclear structure as the proximity of closed nuclear shells and the even-odd effect. Conclusions. The measurement results indicate the presence of a fine structure in the resulting mass distribution of 232Th photofission product yields, which is manifested in increased yields of products localised in the mass regions 133-134, 138-139, and 143-144. The obtained theoretical output values calculated using the GEF 2020 / 1.1 and Talys 1.95 codes describe in general terms and predict the fine structure of the mass distribution of 232Th photofission products

Recent developments in highly basic N-heterocyclic iminato ligands in actinide chemistry.

In the last decade, major conceptual advances in the chemistry of actinide molecules and materials have been made to demonstrate their distinct reactivity profiles as compared to lanthanide and transition metal compounds, but some difficult questions remain concerning the intriguing stability of low-valent actinide complexes, and the importance of the 5f-orbitals in reactivity and bonding. The imidazolin-2-iminato moiety has been extensively used in ligands for the advancement of actinide chemistry owing to its unique capability of stabilizing the reactive and highly electrophilic metal ions by virtue of its strong electron donation and steric tunability. The current review article describes recent developments in the chemistry of light actinide metal ions (thorium and uranium) bearing these N-heterocyclic iminato moieties as supporting ligands. In addition, the effect of ring expansion of the N-heterocycle on the catalytic aptitude of the organoactinides is also described herein. The synthesis and reactivity of actinide complexes bearing N-heterocyclic iminato ligands are presented, and promising apposite applications are also presented. The current review focuses on addressing the catalytic behavior of actinide complexes with oxygen-containing substrates such as in the Tishchenko reaction, hydroelementation processes, and polymerization reactions. Actinide complexes have also found new catalytic applications, as demonstrated by the potent chemoselective carbonyl hydroboration and tandem proton-transfer esterification (TPTE) reaction, featuring coupling between an aldehyde and alcohol.

Octupole correlations in light actinides from the interacting boson model based on the Gogny energy density functional

The quadrupole-octupole coupling and the related spectroscopic properties have been studied for the even-even light actinides $^{218-238}$Ra and $^{220-240}$Th. The Hartree-Fock-Bogoliubov approximation, based on the Gogny-D1M energy density functional, has been employed as a microscopic input, i.e., to obtain (axially symmetric) mean-field potential energy surfaces as functions of the quadrupole and octupole deformation parameters. The mean-field potential energy surfaces have been mapped onto the corresponding bosonic potential energy surfaces using the expectation value of the $sdf$ Interacting Boson Model (IBM) Hamiltonian in the boson condensate state. The strength parameters of the $sdf$-IBM Hamiltonian have been determined via this mapping procedure. The diagonalization of the mapped IBM Hamiltonian provides energies for positive- and negative-parity states as well as wave functions which are employed to obtain transitional strengths. The results of the calculations compare well with available data from Coulomb excitation experiments and point towards a pronounced octupole collectivity around $^{224}$Ra and $^{226}$Th.

Signatures of octupole shape phase transitions in radioactive nuclei

We analyze the octupole deformations and the related collective excitations in medium-heavy and heavy nuclei based on the microscopic framework of the nuclear energy density functional theory. Constrained self-consistent mean-field calculation with a given energy density functional is performed to provide for each nucleus a potential energy surface with axial quadrupole and octupole shape degrees of freedom. Spectroscopic properties are computed by means of the interacting-boson Hamiltonian, which is determined by mapping the fermionic potential energy surface onto the bosonic counterpart. The overall systematics of the calculated spectroscopic observables exhibit phase transitional behaviors between stable octupole deformation and octupole vibration characteristic of the octupole-soft potential within the set of nuclei in light actinide and rare-earth regions, Th, Ra, Sm, Gd, and Ba isotopes, where octupole shapes are most likely to occur.

Kinetic energy distribution for photofission of light actinides

The scission point model has been used to calculate the total kinetic energy (TKE) as a function of fission fragments for photofission reactions. By comparing the calculated TKE values with the available experimental data, the deformation parameters of the fission fragments are obtained in the scission point model. The results show that the deformation parameters of the fission fragments have a large change near the symmetrical region. TKE distribution has been investigated for neutron-induced fission, spontaneous fission, and photofission to predict actinide TKE distribution. This indicates that the TKE distribution depends on the mass and atomic number of compound nuclei and, of course, the excitation energy. The odd-even effect plays an important role in predicting TKE distribution behavior. Also, TKE distribution has a similar trend for all isotopes and the TKE distribution of spontaneous fission is significantly different from the TKE distribution of photofission. At last, the total kinetic energy distributions for the photofission fragments of light actinides are evaluated in the scission point model.

Enhancement of the spin–orbit coupling by strong electronic correlations in transition metal and light actinide compounds

A simple variational argument is presented which indicates that the spin–orbit coupling in itinerant systems can be enhanced by strong electronic correlations. The importance of the enhancement in the formation of the giant magnetic anisotropy found in the metallic paramagnetic and magnetically ordered states of compounds containing transition metal and light actinide elements (such as tetragonal Sr2RhO4, Sr2IrO4, the cubic uranium monochalcogenides and tetragonal URu2Si2) is discussed.

Electronic correlation induced expansion of Fermi pockets inδ-plutonium

Plutonium is a critically important material as the behavior of its 5f-electrons stands midway between the metallic-like itinerant character of the light actinides and localized atomic-core-like character of the heavy actinides. The delta-phase of plutonium (delta-Pu), while still itinerant, has a large coherent Kondo peak and strong electronic correlations coming from its near-localized character. Using sophisticated Gutwiller wavefunction and dynamical mean-field theory correlated theories, we study for the first time the Fermi surface and associated mass renormalizations of delta-Pu together with calculations of the de Haas-van Alphen (dHvA) frequencies. We find a large (200%) correlation-induced volume expansion in both the hole and electron pockets of the Fermi surface in addition to an intermediate mass enhancement. All of the correlated electron theories predict, approximately, the same hole pocket placement in the Brillouin zone, which is different from that obtained in conventional density-functional band-structure theory, whereas the electron pockets from all theories are in, roughly, the same place.

Parameter-free solution of the Bohr Hamiltonian for actinides in the octupole mode

An analytic, parameter-free (up to overall scale factors) solution of the Bohr Hamil- tonian involving axially symmetric quadrupole and octupole deformations, as well as an infinite well potential, is obtained, after separating variables in a way reminiscent of the Variable Moment of Inertia (VMI) concept. Normalized spectra and B(EL) ratios are found to agree with experimental data for 226Ra and 226Th, the nuclei known to lie closest to the border between octupole deformation and octupole vibrations in the light actinide region

"Beat" Patterns of Odd-Even Staggering in Octupole Bands of Light Actinides

The Δ I = 1 staggering (odd-even staggering) in octupole bands of light actinides. is found to exhibit a "beat" behaviour as a function of the angular momentum J, forcing us to revise the traditional belief that this staggering decreases gradually to, zero and then remains at this zero value. Various algebraic models (spf-Interacting Boson Model, spdf-IBM, Vector Boson Model, Nuclear Vibron Model) predict in their su(3) limits constant staggering for this case, being thus unable to describe the "beat" behaviour. An explanation of the "beat" behaviour is given in terms of two Dunham expansions (expansions in terms of powers of I ( I + 1) ) with slightly different sets of coefficients for the ground state band and the negative parity band, the difference in the values of the coefficients being attributed to Coriolis couplings to other negative parity bands.

Assessing Relativistic Effects and Electron Correlation in the Actinide Metals Th to Pu

Density functional theory (DFT) calculations are employed to explore and assess the effects of the relativistic spin–orbit interaction and electron correlations in the actinide elements. Specifically, we address electron correlations in terms of an intra-atomic Coulomb interaction with a Hubbard U parameter (DFT + U). Contrary to recent beliefs, we show that for the ground-state properties of the light actinide elements Th to Pu, the DFT + U makes its best predictions for U = 0. Actually, our modeling suggests that the most popular DFT + U formulation leads to the wrong ground-state phase for plutonium. Instead, extending DFT and the generalized gradient approximation (GGA) with orbital–orbital interaction (orbital polarization; OP) is the most accurate approach. We believe the confusion in the literature on the subject mostly originates from incorrectly accounting for the spin–orbit (SO) interaction for the p1/2 state, which is not treated in any of the widely used pseudopotential plane-wave codes. Here, we show that for the actinides it suffices to simply discard the SO coupling for the p states for excellent accuracy. We thus describe a formalism within the projector-augmented-wave (PAW) scheme that allows for spin–orbit coupling, orbital polarization, and non-collinear magnetism, while retaining an efficient calculation of Hellmann–Feynman forces. We present results of the ground-state phases of all the light actinide metals (Th to Pu). Furthermore, we conclude that the contribution from OP is generally small, but substantial in plutonium.

Protactinium(V) in aqueous solution: a light actinide without actinyl moiety

Abstract This review highlights recent data on the complexation of Pa(V) with inorganic (fluoride and sulphate) and organic (oxalate, nitrilotriacetate, diethylenetriaminepentaacetate) ligands in solution. New thermodynamic parameters relative to the complexation of Pa(V) with sulphate are presented. The review also includes gas phase and theoretical studies focused on the interaction of Pa(V) in the dioxo and oxo forms with water.

Basic Nuclear Structure Features of SHN and Perspectives at S$^{3}$

After more than half a century of research addressing the synthesis and nuclear structure of superheavy nuclei (SHN), a boost for its progress is expected from the advent of new instrumentation. An order of magnitude in beam intensity increase is envisaged to be provided by new powerful accelerators such as the new DC280 cyclotron at the SHE factory of FLNR/JINR or the superconducting linac at SPIRAL2 of GANIL. In addition, new ion-optical installations like the separator-spectrometer set-up S3 with two complementary detection systems SIRIUS and LEB will provide a substantial sensitivity increase for classically pursued routes like decay spectroscopy after separation (DSAS), and alternative and complementary methods such as high precision mass measurements and laser spectroscopy. Decay spectroscopy has proven in the past to be a powerful tool to study the low-lying nuclear structure of heavy and superheavy nuclei. Single particle levels and other structure features like K isomerism, being important in the fermium–nobelium region as well as for the route towards spherical shell stabilised SHN, have been investigated almost up to the limit posed by the sensitivity of the present-day instrumentation. Precision mass measurements and laser spectroscopy will offer the possibility to study alternative features such as binding energies, charge radii and quadrupole moments. At the magnetic spectrometer VAMOS of GANIL with the recently improved mass resolution and the development of Z identification, deep-inelastic reactions like multi-nucleon transfer can be used to reach more neutron-rich nuclei in the region of light actinides, possibly being extended towards higher Z.

Correlating Schiff Moments in the Light Actinides with Octupole Moments.

We show that the measured intrinsic octupole moments of ^{220}Rn, ^{224}Ra, and ^{226}Ra constrain the intrinsic Schiff moments of ^{225}Ra, ^{221}Rn, ^{223}Rn, ^{223}Fr, ^{225}Ra, and ^{229}Pa. The result is a dramatically reduced uncertainty in intrinsic Schiff moments. Direct measurements of octupole moments in odd nuclei will reduce the uncertainty even more. The only significant source of nuclear-physics error in the laboratory Schiff moments will then be the intrinsic matrix elements of the time-reversal noninvariant interaction produced by CP-violating fundamental physics. Those matrix elements are also correlated with octupole moments, but with a larger systematic uncertainty.

Development of nuclear chemistry at Mainz and Darmstadt

Abstract This review describes some key accomplishments of Günter Herrmann such as the establishment of the TRIGA Mark II research reactor at Mainz University, the identification of a large number of very neutron-rich fission products by fast, automated chemical separations, the study of their nuclear structure by spectroscopy with modern detection techniques, and the measurement of fission yields. After getting the nuclear chemistry group, the target laboratory, and the mass separator group established at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, a number of large international collaborations were organized exploring the mechanism of deeply inelastic multi-nucleon transfer reactions in collisions of Xe and U ions with U targets, Ca and U ions with Cm targets, and the search for superheavy elements with chemical separations after these bombardments. After the Chernobyl accident, together with members of the Institute of Physics, a powerful laser technique, the resonance ionization mass spectometry (RIMS) was established for the ultra-trace detection of actinides and long-lived fission products in environmental samples. RIMS was also applied to determine with high precision the first ionization potentials of actinides all the way up to einsteinium. In the late 1980ies, high interest arose in results obtained in fusion-evaporation reactions between light projectiles and heavy actinide targets investigating the chemical properties of transactinide elements (Z≥104). Remarkable was the observation, that their chemical properties deviated from those of their lighter homologs in the Periodic Table because their valence electrons are increasingly influenced by relativistic effects. These chemical results could be reproduced with relativistic quantum-chemical calculations. The present review is selecting and describing examples for fast chemical separations that were successful at the TRIGA Mainz and heavy-ion reaction studies at GSI Darmstadt.

The surface energy and stress of metals

We investigated surface properties of metals by performing first-principles calculations. A systematic database was established for the surface relaxation, surface energy (γ), and surface stress (τ) for metallic elements in the periodic table. The surfaces were modeled by multi-layered slab structures along the direction of low-index surfaces. The surface energy γ of simple metals decreases as the atomic number increases in a given group, while the surface stress τ has its minimum in the middle. The transition metal series show parabolic trends for both γ and τ with a dip in the middle. The dip occurs at half-band filling due to a long-range Friedel oscillation of the surface charge density, which induces a strong stability to the Peierls-like transition. In addition, due to magnetic effects, the dips in the 3d metal series are shallower and deeper for γ and τ, respectively, than those of the 4d and 5d metals. The surface stress of the transition metals is typically positive, only Cr and Mn have a negative τ for the (100) surface facet, indicating that they are under compression. The light actinides have an increasing γ trend according to the atomic number. The present work provides a useful and consistent database for the theoretical modelling of surface phenomena.

The proton microscopic optical potential based on Skyrme interaction

The proton microscopic optical potential (MOP) based on Skyrme interaction has been achieved by the Green function method in the nuclear matter, and given by the local density approximation (LDA) for finite nuclei. The reaction cross-sections, elastic scattering angular distributions, analyzing powers, and spin-rotation functions are predicted by the obtained proton MOP with Skyrme interaction SkC in the mass range of target nuclei 24[Formula: see text][Formula: see text][Formula: see text]A[Formula: see text][Formula: see text][Formula: see text]209 with incident proton energy below 100[Formula: see text]MeV. These observables are further predicted for some light nuclei and actinide nuclei below 100[Formula: see text]MeV. The prediction is compared with existing experimental data. It is revealed that the obtained proton MOP based on Skyrme interaction SkC can satisfactorily describe the proton–nucleus elastic scattering.