Superheavy Elements Research Articles

Relativistic coupled-cluster calculation of the electric dipole polarizability and correlation energy of Cn, Nh+ , and Og: Correlation effects from lighter to superheavy elements

We employ a fully relativistic coupled-cluster theory to calculate the ground-state electric dipole polarizability and electron correlation energy of superheavy elements Cn, Nh$^+$ and Og. To assess the trend of electron correlation as function of $Z$, we also calculate the correlation energies for three lighter homologs--Zn, Cd and Hg; Ga$^+$, In$^+$ and Tl$^+$; Kr, Xe and Rn--for each superheavy elements. The relativistic effects and quantum electrodynamical corrections are included using the Dirac-Coulomb-Breit Hamiltonian with the corrections from the Uehling potential and the self-energy. The effects of triple excitations are considered perturbatively in the theory. Furthermore, large bases are used to test the convergence of results. Our recommended values of polarizability are in good agreement with previous theoretical results for all SHEs. From our calculations we find that the dominant contribution to polarizability is from the valence electrons in all superheavy elements. Except for Cn and Og, we observe a decreasing contribution from lighter to superheavy elements from the Breit interaction. For the corrections from the vacuum polarization and self-energy, we observe a trend of increasing contributions with $Z$. From energy calculations, we find that the second-order many-body perturbation theory overestimates the electron correlation energy for all the elements considered in this work.

Fair-wind gas cell for the UniCell setup

A novel UniCell setup for studies of superheavy elements (SHE) was proposed recently. Here we deploy the concept of the so called ”Fair-wind gas cell” and suggest a new buffer gas stopping cell, that may serve as an optional main part of the UniCell setup. Advantages of this new optional gas cell compared to the previous version for the UniCell setup consists in the use of an intense compulsory buffer gas flow, as a driving force for ion transport through the high-density gas stopping cell, combined with an RF-only funnel. This allows a fast and highly efficient extraction of ions from the gas stopping cell without application of traditional DC gradient fields. For the reduction of the pure buffer gas consumption the intense flow is recirculating in a loop. The functionality of the proposed new gas stopping cell was explored by detailed gas dynamic and Monte Carlo ion-trajectory simulations, the results of which are presented and discussed. They demonstrate the feasibility of the fair-wind gas stopping cell for the application in SHE research.

Prediction of half-lives of even–even superheavy nuclei

α-decay half-lives (-values) of even–even and superheavy nuclei (SHN) are determined employing interaction potential involving Coulomb and proximity potentials. The obtained results are compared with the experimental ones and to assess the precision of the present model in reproducing the experimental half-lives, a comparison is drawn with the other methods as well. We require disintegration energy (Q α -values) as an input in order to predict the (-values) of an experimentally unknown SHN. So, utilizing periodic-orbit theory within microscopic-macroscopic formalism, we have calculated the binding energies and thereafter, Q α -values of known SHN. The results are found to be in good agreement with the experimental ones. Subsequently, we predict the logarithmic values of ’s for even–even unknown SHN whose atomic numbers lie in 118 ⩽ Z ⩽ 126 regime and compare our results with those calculated employing other theoretical methods. Also, the study of spontaneous fission half-lives and branching ratios leads us to predict the SHN which can be identified through α-decay chains in the laboratories. We believe that this work can play a significant role in the experiments leading to the synthesis and identification of new superheavy elements.

Microscopic calculation of fission product yields with particle-number projection

Fission fragments' charge and mass distribution is an important input to applications ranging from basic science to energy production or nuclear non-proliferation. In simulations of nucleosynthesis or calculations of superheavy elements, these quantities must be computed from models, as they are needed in nuclei where no experimental information is available. Until now, standard techniques to estimate these distributions were not capable of accounting for fine-structure effects, such as the odd-even staggering of the charge distributions. In this work, we combine a fully-microscopic collective model of fission dynamics with a recent extension of the particle number projection formalism to provide the highest-fidelity prediction of the primary fission fragment distributions for the neutron-induced fission of $^{235}$U and $^{239}$Pu. We show that particle number projection is an essential ingredient to reproduce odd-even staggering in the charge yields and benchmark the performance of various empirical probability laws that could simulate its effect. This new approach also enables for the first time the realistic determination of two-dimensional isotopic yields within nuclear density functional theory.

Phenomenological Approach to Extrapolation of Nuclear Binding Energies for Superheavy Elements

Phenomenological Approach to Extrapolation of Nuclear Binding Energies for Superheavy Elements

Ion-optical design and multiparticle tracking in 3D magnetic field of the gas-filled recoil separator SHANS2 at CAFE2

The CAFE2 (China Accelerator Facility for superheavy Elements) is a new facility constructed at IMP-CAS (Institute of Modern Physics, Chinese Academy of Sciences). It is based on the upgrade of a superconducting linear accelerator. A new gas-filled recoil separator SHANS2 (Spectrometer for Heavy Atoms and Nuclear Structure-2) with a total flight length path of 5.85 m at the CAFE2 is designed to synthesize and study the superheavy elements, including their physical and chemical properties. The maximum acceptable divergence angles of the SHANS2 are ±70 mrad and ±113 mrad in horizontal and vertical directions, respectively, and the maximum magnetic rigidity is 2.5 Tm. The ion-optical design and simulation are investigated in detail, including the first and the fifth order beam optics. The magnets design and magnetic field calculation are presented. Using the 3D field maps, a multiparticle tracking study is carried out for the design validation, trajectory analysis, and performance evaluation.

Residual np-interaction and mass predictions in transfermium region

We study the consistency of local mass relation approach in its application to prediction of nuclear masses in the region of superheavy elements. Binding energy calculations are carried out for nuclei with [Formula: see text] using formulas for evaluation of residual [Formula: see text]-interaction. The results are found to be in good agreement with the experimental data AME2016. We also make predictions for characteristics of [Formula: see text]-decay in isotopes [Formula: see text]–106, [Formula: see text]–157.

Unexpectedly enhanced α -particle preformation in Ti48 probed by the ( p,pα ) reaction

The formation of $\alpha$ particle on nuclear surface has been a fundamental problem since the early age of nuclear physics. It strongly affects the $\alpha$ decay lifetime of heavy and superheavy elements, level scheme of light nuclei, and the synthesis of the elements in stars. However, the $\alpha$-particle formation in medium-mass nuclei has been poorly known despite its importance. Here, based on the $^{48}{\rm Ti}(p,p\alpha)^{44}{\rm Ca}$ reaction analysis, we report that the $\alpha$-particle formation in a medium-mass nucleus $^{48}{\rm Ti}$ is much stronger than that expected from a mean-field approximation, and the estimated average distance between $\alpha$ particle and the residue is as large as 4.5 fm. This new result poses a challenge of describing four nucleon correlations by microscopic nuclear models.

Tensor force effect on the neutron shell closure in super-heavy elements

A systematic study of the effect of tensor force on the evolution of shell structure in even-even super-heavy nuclei in the region of proton numbers Z=114, 120 and 126 and in the region of neutron numbers 178 $\le$ N $\le$ 188 is presented. We use, in this investigation, the Hartree-Fock framework by means of different types of Skyrme functionals in two cases with and without tensor force. The Bardeen-Cooper-Schriefer (BCS) approximation has been used to treat the pairing correlations. By investigating structural and decay properties of nuclei under consideration, it is found that N=184 shell gap is more enhanced by the tensor interaction which depends on the isoscalar tensor coupling constant $C_0^J$ of the used Skyrme interactions. In the case without tensor interaction, this gap is significant only for T22, T24, T42 and SLy5. So, it disappears with T46, T64 and T66, and is too weak for T26, T44 and T62. Without exception, the shell gap at N=184 becomes more pronounced when the tensor part is taken into account.

Co-precipitation behaviour of single atoms of rutherfordium in basic solutions.

All superheavy elements (SHEs), with atomic numbers (Z) ≥104, have been artificially synthesized one atom at a time and their chemical properties are largely unknown. Because these heavy nuclei have short lifetimes as well as extremely low production rates, chemical experiments need to be carried out on single atoms and have mostly been limited to adsorption and extraction. We have now investigated the precipitation properties of the SHE Rf (Z = 104). A co-precipitation method with samarium hydroxide had previously established that the co-precipitation behaviour of a range of elements reflected these elements' tendency to form hydroxide precipitates and/or ammine complex ions. Here we investigated co-precipitation of Rf in basic solutions containing NH3 or NaOH. Comparisons between the behaviour of Rf with that of Zr and Hf (lighter homologues of Rf) and actinide Th (a pseudo-homologue of Rf) showed that Rf does not coordinate strongly with NH3, but forms a hydroxide (co)precipitate that is expected to be Rf(OH)4.

Probing precipitation properties.

Superheavy elements are short-lived and only available on a single-atom level, making their chemical properties very challenging to study. Now, through their co-precipitation with samarium, single atoms of rutherfordium have been shown to form hydroxide complexes but not ammine ones.

Quasifission and fusion-fission lifetime studies for the superheavy element Z=120

We study the quasifission and fusion-fission lifetimes for a number of fusion reactions used to synthesize the superheavy element $Z=120$ using a statistical method within the framework of the dinuclear system model. In particular, influence of the target orientation and angular momentum on such lifetimes have been investigated. The quasifission and fusion-fission lifetimes have been compared very well with that of available experiments on successful superheavy element synthesis. We notice further the predicted quasifission and fusion-fission lifetimes of the projectile-target combinations used for the synthesis of the superheavy element $Z=120$ also show the similar trend. Furthermore, the fusion-fission lifetime is seen to somewhat decrease with the increase of the angular momentum as well as beam energy. Little effect is seen on fusion barrier of the reaction and fission barrier of superheavy compound nucleus. Variation of quasifission lifetime is also not much with orientation angle, beam energy and fission barrier of the superheavy compound nuclei. Hence, this lifetime study does not provide any good reason why the attempted reactions have failed to synthesize the superheavy nuclei $Z=120$. Furthermore, consideration of the fusion barrier, fissility, mass asymmetry, deformation parameter, fission barrier, etc., leads us to reveal that optimal colliding energy is important to have the largest evaporation residue cross section for any chosen reaction so that it is well within the measurable limit for a specific experimental set up.

Combination of DGA and LN Columns: A Versatile Option for Isotope Production and Purification at Oak Ridge National Laboratory

ABSTRACT The chromatographic resins DGA and LN have been used sequentially to separate curium, californium, plutonium, and various fission products (FPs) to obtain products with a pure radioisotope or a radioelement with high isotopic purity. This 2-step combination of resins has found applications in the 252Cf and 238Pu campaigns performed at Oak Ridge National Laboratory. Experiments have been carried out in glove boxes, shielded caves, and hot cells, demonstrating that these resins are adequate and maintain their performance in highly radiolytic environments. Using these resins has led to the recovery of curium highly enriched (>95%) in 248Cm, the clean separation of 251Cf for the superheavy element research, and the recovery of 147Pm from the FP stream obtained during the 238Pu production campaign while demonstrating that the raffinate post DGA is essentially free of transuranic elements.

Rapid extraction of short-lived isotopes from a buffer gas cell for use in gas-phase chemistry experiments. Part I: Off-line studies with 219Rn and 221Fr

To study the chemical properties of the heaviest elements, a fast and efficient stopping and extraction of the highly energetic residues from heavy ion fusion reactions into the chemistry setup is essential. Currently used techniques like Recoil Transfer Chambers (RTC) relying on gas flow extraction provide high efficiencies for chemically non-reactive volatile species, but operate at extraction times textr of about 0.5s or more. Buffer Gas Cells (BGC) with electric and Radio-Frequency (RF) fields offer much faster extraction times. Here, we demonstrate the successful coupling of a BGC to a gas chromatography setup as is used for studies of chemical properties of superheavy elements. Using 223Ra and 225Ac recoil ion sources providing 219Rn and 221Fr ions for off-line tests, an extraction time textr = 55(4)ms and an extraction efficiency of 35(3)% were achieved for the non-reactive 219Rn, while 221Fr was retained. The results show a BGC-based setup to be suitable for gas-phase experiments with short-lived volatile transactinide elements like Cn and Fl with half-lives substantially below 1s.

Evaluation of the characteristics of a hybrid power nuclear mini-reactor fueled by super-heavy elements

The concept of a hybrid mini-reactor capable of operating in the mode of a nuclear fission reactor (on fast neurons), in the mode of a radionuclide source and simultaneously in both modes is considered. It is proposed to use the most long-lived isotopes of the 114th, 126th, and possibly 120th elements as fuel for such a mini-reactor. Such nuclides have not yet been obtained in laboratories around the world. The neutron effective cross sections and macroscopic cross sections for the nuclei of super-heavy elements are estimated. A simple and effective mathematical model of the neutron-physical calculation of a mini-reactor with fuel based on super-heavy nuclei is proposed. The model is based on the one-group diffusion approximation. The uncertainties of the cross sections are so great that the use of more accurate and high-precision calculation models can hardly be justified. The results of neutron-physical calculations of a mini-reactor with fuel based on the longest-lived isotopes of the 114th and 126th elements are presented. The critical mass of a ball (without a reflector) made from 114Fl will be 1.492 kg; the critical radius will be less than 2.48 cm. (For element 342126 1.474 kg and less than 2.33 cm respectively.)

A dynamical study of fusion hindrance with the Nakajima–Zwanzig projection method

Abstract A new framework is proposed for the study of collisions between very heavy ions which lead to the synthesis of Super-Heavy Elements (SHE), to address the fusion hindrance phenomenon. The dynamics of the reaction is studied in terms of collective degrees of freedom undergoing relaxation processes with different time scales. The Nakajima–Zwanzig projection operator method is employed to eliminate fast variables and derive a dynamical equation for the reduced system with only slow variables. There, the time evolution operator is renormalised and an inhomogeneous term appears, which represents a propagation of the given initial distribution. The term results in a slip to the initial values of the slow variables. We expect that gives a dynamical origin for the so-called “injection point $s$” introduced by Swiatecki et al. in order to reproduce absolute values of measured cross sections for SHE. A formula for the slip is given in terms of physical parameters of the system, which confirms the results recently obtained with a Langevin equation, and permits us to compare various incident channels.

Gas phase synthesis of 4d transition metal carbonyl complexes with thermalized fission fragments in single-atom reactions

Abstract The formation of carbonyl complexes using atom-at-a-time quantities of short-lived transition metals from fusion and fission reactions was reported in 2012. Numerous studies focussing on this chemical system, which is also applicable for the superheavy elements followed. We report on a novel two-chamber approach for the synthesis of such complexes that allows spatial decoupling of thermalization and gas-phase carbonyl complex synthesis. Neutron induced fission on 235U and spontaneous fission of 248Cm were employed for the production of the fission products. These were stopped inside a gas volume behind the target and flushed with an inert-gas flow into a second chamber. This was flushed with carbon monoxide to allow the gas-phase synthesis of carbonyl complexes. Parameter studies of the transfer from the first into the second chamber as well as on the carbonyl complex formation and transport processes have been performed. High overall efficiencies of more than 50% were reached rendering this approach interesting for studies of superheavy elements. Our results show that carbonyl complex formation of thermalized fission products is a single-atom reaction, and not a hot-atom reaction.

Level structures of the transfermium odd-odd nucleus Md252

Low-energy level scheme of doubly odd transfermium nucleus ${}_{101}^{252}{\mathrm{Md}}_{151}$ is constructed using our well-tested two-quasiparticle rotor model with explicit inclusion of residual n-p interaction contribution. Energy levels thus deduced are examined critically to assign spin-parity ${J}^{\ensuremath{\pi}}K$ and two-quasiparticle (2qp) configurations to the $^{252}\mathrm{Md}$ ground state and other energy levels with ${E}_{x}<400$ keV. Our low-energy level structures are then examined to predict a high-spin $({J}^{\ensuremath{\pi}}={8}^{+})$ long-lived isomer with ${E}_{x}\ensuremath{\approx}125$ keV and possibly also a lower-lying short-lived isomeric state. Comparison with $^{256}\mathrm{Lr}$ $(\ensuremath{\alpha})$ populated $^{252}\mathrm{Md}$ excited states leads to ${J}^{\ensuremath{\pi}}K$ and 2qp assignment to each of these experimentally postulated levels. Further, the five $\ensuremath{\gamma}$'s ascribed to $^{252}\mathrm{Md}$ from $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence experiments are placed in our evaluated levels corresponding to $\mathrm{\ensuremath{\Delta}}I=2$ transition in each case. Additionally, exploration of the upward extended radioactive connection of $^{232}\mathrm{Th}$ heading the $A=4n$ naturally occurring radioactive series to the heaviest known superheavy element with $A=4n$, namely ${}_{111}^{272}{\mathrm{Rg}}_{161}$, has led us to establish landmark position of $^{252}\mathrm{Md}$ in this $^{272}\mathrm{Rg}\text{\ensuremath{-}}^{232}\mathrm{Th}$ extended decay chain.

Enhanced Fusion Mechanisms Towards Synthesizing Superheavy Elements

In nature all of the heavy elements are produced by nuclear fusion reactions, mostly in supernova explosions and neutron star collisions, so, this is to date the only known and proven mechanism to produce heavy elements in usable quantities. In this work we approach a difficult challenge, namely, the possibility of fusion of heavy elements, taking as a test case the heaviest observationally stable element - ²³⁸U, showing that it is feasible, at least in principle with the help of existing technologies. The main idea behind is to show that fusion of lighter - than z=184 - nuclei is conceptually viable examining the tunnel effect assisted by an auxiliary field that will produce a Sauter like effect, and this is the pathway to explore the synthesis of elements higher than z=118. The production of theoretical untested elements like Unoctquadium-184 or close Z species could open a new chapter in the physics of super-heavy elements, and leads to a deeper understanding of nuclear decay channels and stability conditions. Nuclear fusion of heavy elements will open the breach to produce neutron rich elements, so we may obtain a deep insight into the physics of the island of stability. This work will review basic aspects of fusion physics related to the assisted fusion mechanism. An enhanced fusion perspective is found generalizing the work of [1] to space dependent fields and the cases of ²H, ¹⁰⁶Pd and ²³⁸U are presented for several test fields. A final section reviewing laser confinement fusion actual experiments capable of achieving the required energies is also reported.

Enhanced Fusion Mechanisms Towards Synthesizing Superheavy Elements

In nature all of the heavy elements are produced by nuclear fusion reactions, mostly in supernova explosions and neutron star collisions, so, this is to date the only known and proven mechanism to produce heavy elements in usable quantities. In this work we approach a difficult challenge, namely, the possibility of fusion of heavy elements, taking as a test case the heaviest observationally stable element - ²³?U, showing that it is feasible, at least in principle with the help of existing technologies. The main idea behind is to show that fusion of lighter - than z=184 - nuclei is conceptually viable examining the tunnel effect assisted by an auxiliary field that will produce a Sauter like effect, and this is the pathway to explore the synthesis of elements higher than z=118. The production of theoretical untested elements like Unoctquadium-184 or close Z species could open a new chapter in the physics of super-heavy elements, and leads to a deeper understanding of nuclear decay channels and stability conditions. Nuclear fusion of heavy elements will open the breach to produce neutron rich elements, so we may obtain a deep insight into the physics of the island of stability. This work will review basic aspects of fusion physics related to the assisted fusion mechanism. An enhanced fusion perspective is found generalizing the work of [1] to space dependent fields and the cases of ²H, ¹??Pd and ²³?U are presented for several test fields. A final section reviewing laser confinement fusion actual experiments capable of achieving the required energies is also reported.