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International audience; We present a scheme to achieve coherent polarization rotation without multipolar or rotating external magnetic bias nor complex cascaded emitters, by exploiting artificially engineered strong uniaxial anisotropy in intermetallic heterostructures of rare-earth and transition metals. By replacing the FM layer of the spintronic emitter with a carefully designed FeCo/TbCo2/FeCo heterostructure, we demonstrated Stoner-Wolfarth-like coherent rotation of the THz polarization only by a unipolar variation of the strength of the hard axis field. In a second step we demonstrated the magnetoelectric control of the polarization direction. These results improve greatly the feasibility of fast polarization switchable integrated THz sources impacting practical applications such as ultrabroadband THz spectroscopic ellipsometry without rotating elements, or polarization modulated high speed wireless data communications, but also fundamental physical studies into ultrafast terahertz optospintronics.

We report the first ionization potentials (IP1) of the heavy actinides, fermium (Fm, atomic number Z = 100), mendelevium (Md, Z = 101), nobelium (No, Z = 102), and lawrencium (Lr, Z = 103), determined using a method based on a surface ionization process coupled to an online mass separation technique in an atom-at-a-time regime. The measured IP1 values agree well with those predicted by state-of-the-art relativistic calculations performed alongside the present measurements. Similar to the well-established behavior for the lanthanides, the IP1 values of the heavy actinides up to No increase with filling up the 5f orbital, while that of Lr is the lowest among the actinides. These results clearly demonstrate that the 5f orbital is fully filled at No with the [Rn]5f(14)7s(2) configuration and that Lr has a weakly bound electron outside the No core. In analogy to the lanthanide series, the present results unequivocally verify that the actinide series ends with Lr.

We use the well-known Wentzel–Kramers–Brillouin (WKB) barrier penetration probability to calculate α-decay branching ratios for ground and excited states of heavy even–even nuclei of Fermium ( 248 – 254 Fm), Californium ( 244 – 252 Cf), Curium ( 238 – 248 Cm) and Plutonium ( 234 – 244 Pu) with 94 ≤ Z p ≤ 100. We obtained the branching ratios for the excited states of daughter nucleus by the α-decay energy (Qα), the angular momentum of α-particle ( l α ), and the excitation probability of the daughter nucleus with the excitation energy of state l in the daughter nucleus (i.e. E l ⁎ ). α-Decay half-lives have been evaluated by using the proximity potential model for the heavy even–even nuclei. We have reported the half-lives and compared the results with the experimental data. The theoretical branching ratios of α-transitions in our calculation are found to agree with the available experimental data well for 0 → + 0+, 0 → + 2+, 0 → + 4+, 0 → + 6+ and 0+ → 8+ α-transitions.

Research on heavy actinides has experienced an increased interest in the last few years due to new synthetic techniques and recent technological advances that have allowed for obtaining important information even from very small samples. This area presents challenges not only from the experimental point of view but also from the theoretical perspective. This work deals with a multiconfigurational CASSCF and NEVPT2 benchmark study based on a two-step methodology that considers first correlation effects and then the spin-orbit coupling applied to berkelium (Bk), californium (Cf), einsteinium (Es) and fermium (Fm) hexahalides. Optical properties, such as f → d transitions and crystal-field parameters, have been calculated and rationalized. The results for these trivalent actinides indicate that the electronic structure of the low-lying states is reproduced accurately with small basis sets. The ground-state multiplets are isolated, in the same manner as their isoelectronic lanthanide counterparts. In the case of tetravalent berkelium, the picture is different regarding the electronic structure where crystal-field theory fails due to considerable ligand-to-metal charge transfer contributions to the ground state.

This study is focused on the structural, elastic and electronic properties of fermium monopnictide compounds FmX (X = P, As, and Sb) in rock-salt (B1), CsCl (B2), and zinc-blend (B3) structures using the first-principles Full-Potential Linearized Augmented Plane Waves plus local orbitals (FP-L/APW+lo) method, implemented in the WIEN2k code which including the Generalized Gradient Approximation (GGA) and GGA+U as exchange correlation potential. The structural properties were calculated in order to determine the most stable structure and the most stable magnetic phase. Through our structural investigations, we have concluded that these three binaries doesn't exhibit a magnetic nature, certified by nonmagnetic stable phase in nonmagnetic state. The structural obtained results are presented as, lattice constant (a), bulk modulus (B), and its first pressure derivative (B′). The elastic aggregates properties including elastic constants (Cij), Young's modulus (E), shear modulus (G), Poisson's ratio (υ), Keinman parameter (ζ), and anisotropy factor (A). All the compounds are characterized as brittle and anisotropic materials. The electronic structure of these compounds is described by the exhibition of total and partial densities of states (TDOS and PDOS) and band structures. All the compounds are confirmed as metallic materials. The negative values of formation (Ef) reveal that all the compounds are thermodynamically stable.

We use a recently developed version of the configuration method for open shells to study electronic structure of erbium and fermium atoms. We calculate excitation energies of odd states connected to the even ground state by electric dipole transitions, the corresponding transition rates, isotope shift, hyperfine structure, ionization potentials and static scalar polarizabilities. We argue that measuring isotope shift for several transitions can be used to study nuclear deformation in even-even nuclei. This is important for testing nuclear theory and for searching for the hypothetical island of stability. Since erbium and fermium have similar electronic structures, calculations for erbium serve as a guide to the accuracy of the calculations., 10 pages, 1 figure, to be published

The fission of even-even fermium nuclides $^{250\ensuremath{-}260}\mathrm{Fm}$ at low excitation energy was studied using Langevin equations of three-dimensional nuclear-shape parametrization. The mass distributions of fission fragments show a dramatic change from an asymmetric shape for the lighter fermium isotopes to sharp symmetric fission for the heavier isotopes. The time evolution of the nuclear shape on the potential surface reveals that the lighter fermium isotopes showing asymmetric fission are trapped in the second minimum for a substantial length of time before overcoming the second saddle point. This behavior changes dramatically for the compact symmetric fission found in the heavier neutron-rich fermium nuclei that disintegrate immediately after overcoming the first saddle point, without feeling the second barrier, resulting in a fission time two orders of magnitude shorter.

Background: Predicting the properties of neutron-rich nuclei far from the valley of stability is one of the major challenges of modern nuclear theory. In heavy and superheavy nuclei, a difference of only a few neutrons is sufficient to change the dominant fission mode. A theoretical approach capable of predicting such rapid transitions for neutron-rich systems would be a valuable tool to better understand $r$-process nucleosynthesis or the decay of superheavy elements.Purpose: In this work, we investigate for the first time the transition from asymmetric to symmetric fission through the calculation of primary fission yields with the time-dependent generator coordinate method (TDGCM). We choose here the transition in neutron-rich fermium isotopes, which was the first to be observed experimentally in the late 1970s and is often used as a benchmark for theoretical studies.Methods: We compute the primary fission fragment mass and charge yields for $^{254}\mathrm{Fm}, ^{256}\mathrm{Fm}$, and $^{258}\mathrm{Fm}$ from the TDGCM under the Gaussian overlap approximation. The static part of the calculation (generation of a potential energy surface) consists of a series of constrained Hartree-Fock-Bogoliubov calculations based on the D1S, D1M, or D1N parametrization of the Gogny effective interaction in a two-center harmonic oscillator basis. The two-dimensional dynamics in the collective space spanned by the quadrupole and octupole moments $({\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{Q}}_{20},{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{Q}}_{30})$ is then computed with the finite element solver Felix-2.0.Results: The available experimental data and the TDGCM post-dictions are consistent and agree especially on the position in the fermium isotopic chain at which the transition occurs. In addition, the TDGCM predicts two distinct asymmetric modes for the fission of $^{254}\mathrm{Fm}$.Conclusions: Thanks to its intrinsic accounting of shell effects and to its ability to describe the dynamics of the system up to configurations close to scission, the TDGCM is able to describe qualitatively the fission yield transition in the neutron-rich fermium isotopes. This makes it a promising tool to study the evolution of the fission yields far from the valley of stability. The main limitation of the method lies in the presence of discontinuities in the two-dimensional manifold of generator states.

Fission-fragment mass and total-kinetic-energy distributions following fission of the fermium isotopes $^{256,258,260}\text{Fm}$ at low excitation energy have been calculated using the Brownian shape-motion model. A transition from asymmetric fission in $^{256}\text{Fm}$ to symmetric fission in $^{258}\text{Fm}$ is obtained. The total-kinetic-energy distributions for the three isotopes show radically different behaviour due to varying contributions from different fission modes, with a double-humped distribution for $^{258}\text{Fm}$., 2 pages, 3 figures, Contribution to the Proceedings of the IV International Conference on Nuclear Structure and Dynamics (NSD2019), Venice, Italy, 2019

Resonance ionization spectroscopy of nobelium (atomic number 102) reveals its ground-state transition and an upper limit for its ionization potential, paving the way to characterizing even heavier elements via optical spectroscopy. Characterizing the heaviest elements in the periodic table is a gruelling task because they are radioactive, exist only for split seconds at a time and need to be artificially produced in sufficient quantities by complicated procedures. The heaviest element that has been characterized by optical spectroscopy is fermium, which has an atomic number of 100. Mustapha Laatiaoui et al. extend the methods used for fermium to perform optical spectroscopy on nobelium (atomic number 102). Through laser resonance ionization spectroscopy, they identify the ground-state transition of the atom and manage to investigate highly excited states called Rydberg states. This allows them to determine an upper limit for the atomic ionization potential of nobelium. This study opens the door to the characterization of even heavier elements such as lawrencium using optical spectroscopy. Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements1 and theoretical modelling can be performed to high precision2,3, taking into account relativistic effects that scale approximately as the square of the atomic number. However, for the transfermium elements (those with atomic numbers greater than 100), the atomic structure is experimentally unknown. These radioactive elements are produced in nuclear fusion reactions at rates of only a few atoms per second at most and must be studied immediately following their production4, which has so far precluded their optical spectroscopy. Here we report laser resonance ionization spectroscopy of nobelium (No; atomic number 102) in single-atom-at-a-time quantities, in which we identify the ground-state transition 1S0 1P1. By combining this result with data from an observed Rydberg series, we obtain an upper limit for the ionization potential of nobelium. These accurate results from direct laser excitations of outer-shell electrons cannot be achieved using state-of-the-art relativistic many-body calculations5,6,7,8 that include quantum electrodynamic effects, owing to large uncertainties in the modelled transition energies of the complex systems under consideration. Our work opens the door to high-precision measurements of various atomic and nuclear properties of elements heavier than nobelium, and motivates future theoretical work.