Superheavy Elements Research Articles

Chemical Elements in Space

Astrophysical observations give scientists the most essential information about the processes and “rates of production” of elements in nature and their abundance in the Universe. The lightest elements of the Periodic Table—hydrogen, helium, and, partially, lithium—appeared in the first seconds after the birth of the Universe. The first stars “gathered” from them; they enriched the Universe with heavier elements during the evolutionary process, with the participation of which “modern” stars subsequently formed. These stars, in turn, serve as natural factories for the synthesis of heavy elements not only throughout their lives but also during their deaths in supernova outbursts. The recent discovery of the fusion of neutron stars and subsequent studies of their afterglow revealed the features of the formation of superheavy elements in the Universe up to gold and uranium.

150th Anniversary of the Periodic Table of the Chemical Elements

The year 2019 was proclaimed by the UN and UNESCO as the International Year of the Periodic Table of the Chemical Elements; by its beginning, the seventh period of the Table was already filled with new, very heavy elements. According to theoretical predictions, isotopes of superheavy elements with increased stability form a large zone in the form of an island with a vertex located near the “magic” numbers of protons Z = 114 and neutrons N = 184 on the nuclide map. New elements with atomic numbers from 114 to 118 were synthesized in the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research (JINR, Dubna), in 2000–2012 by fusion reactions of target nuclei (heavy actinide isotopes (Z = 94–98)) with bombarding 48Ca ions. The experimental results suggest that there may exist nuclei or elements with atomic numbers greater than 118 and mass greater than 300 amu. A new experimental complex, the Factory of Superheavy Elements (SHEF), was created in Dubna to study the nuclear and electronic structures of new elements and their chemical properties and to synthesize elements from the beginning of the eighth period of the Periodic Table. A new DC-280 accelerator has already been launched in the SHEF, and experiments are planned to begin. The introductory and final parts of my speech at the scientific session of the General Meeting of the Members of the Russian Academy of Sciences are related to the discovery of the Periodic Law published by D.I. Mendeleev 150 years ago. The action of this law in the properties of the heaviest elements represents today one of the most urgent and interesting problems of the natural sciences.

Fusion Dynamics of Low-Energy Heavy-Ion Collisions for Production of Superheavy Nuclei

One of the major motivation of low energy heavy-ion collision is the synthesis of superheavy nuclei. Based on the following two main aspects, various theoretical and experimental research have been performed to study the fusion dynamical process of superheavy nuclei production. The first reason is to elucidate and analyze the synthesis mechanism of superheavy nuclei; the other is to search the favorable incident energy and the best combination of projectile and target to produce new superheavy elements and isotopes of superheavy elements.

Quasifission Dynamics in Microscopic Theories

In the search for superheavy elements quasifission reactions represent one of the reaction pathways that curtail the formation of an evaporation residue. In addition to its importance in these searches quasifission is also an interesting dynamic process that could assist our understanding of many-body dynamical shell effects and energy dissipation thus forming a gateway between deep-inelastic reactions and fission. This manuscript gives a summary of recent progress in microscopic calculations of quasifission employing time-dependent Hartree-Fock (TDHF) theory and its extensions.

Solvent Extraction of Zr and Hf from HCl by Aliquat 336 using a Flow-Type Extraction Apparatus Toward Online Chemical Studies of Element 104, Rutherfordium

ABSTRACTChemical studies of transactinide elements (atomic number Z ≥ 104) are of great importance to understand the relativistic effects; however, the experimental methodology is limited owing to the single atom situation and short lifetimes of the heavy atoms. Herein, we report the successful establishment of a new solvent extraction method for transactinide elements using a flow-type solvent extraction apparatus. The developed apparatus has a reaction unit in which PTFE chips are packed to shorten the time required for the transfer of metal complexes between the aqueous and organic phases. Equilibrium distribution ratios were obtained for Zr and Hf: the homologues of element 104, rutherfordium (Rf), in a short time considering the half-life of 261Rf as 68 s. In addition, the developed extraction apparatus was connected to an online transportation system for the nuclear reaction products at an accelerator, and online solvent extraction experiments were conducted with the short-lived nuclear reaction products of 89m,gZr and 173Hf. Distribution ratios consistent with the equilibrium ratios were successfully acquired. The solvent extraction system for experiments on Rf was thus established, and the optimal experimental conditions were determined.

Improvement of the detection efficiency of a time-of-flight detector for superheavy element search

A time-of-flight (TOF) detector with a large entrance foil (effective area of 154 cm2) was developed as part of the detection system to search for new elements of Z = 119 and beyond at RIKEN. We obtained a detection efficiency of approximately 100% for charged particles passing through the center region of the entrance foil. On the other hand, the detection efficiency decreased to approximately 23% in the edge region of the entrance foil. In this study, the modification of the internal electric field of the TOF detector is considered and realized to improve the detection efficiency. The validity of the modification is investigated by simulation. Furthermore, the detection efficiency is investigated through offline and beam experiments while modifying the internal electric field. The obtained results establish that the detection efficiency is improved by modifying the internal electric field.

Study of Quasielastic Barrier Distributions as a Step towards the Synthesis of Superheavy Elements with Hot Fusion Reactions.

The excitation functions for quasielastic scattering of ^{22}Ne+^{248}Cm, ^{26}Mg+^{248}Cm, and ^{48}Ca+^{238}U are measured using a gas-filled recoil ion separator. The quasielastic barrier distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg (Z=106), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. A new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.

Study of neutron-rich isotopes near N=152 shell closure using Timepix type detectors integrated into the mass separator MASHA

The MASHA facility [1–3] was developed as a high precision mass-spectrometer for heavy and super heavy elements with masses up to 450 a.m.u. It uses ISOL (Isotope Separation On-Line) method. Its unique properties opens great prospective for the investigation of neutron-rich nuclei produced in multinucleon transfer reactions. Mainly nuclei near the neutron N = 126 and N = 152 shell closures are of great interest. This region of nuclei is not so far thoroughly enough investigated while its research has direct relation to the synthesis of super heavy elements. As is known the island of stability close to super heavy elements (Z = 112–118) exists due to the shell effects in nuclei. More detailed investigation of these shell effects can greatly help in the synthesis of next super heavy elements. Heavy neutron rich radon isotopes were produced in the multinucleon transfer reaction 40Ar + 232Th at Flerov Laboratory of Nuclear Reactions, Dubna. Radon isotopes with given masses were detected using two types of detectors: a multi-strip well-type detector (made in Canberra) and a position-sensitive quantum counting hybrid pixel detector of the Timepix type [1]. The latter detector has an array of 256×256 square pixels each with a pitch size of 55 μm for the full sensitive area 14×14 mm2. Radon isotopes implanted into the detector emit then alpha and beta particles until they reach the stable or long-lived isotopes at the end of their decay chains. The positions of radon isotopes, the tracks, times and energies of the beta particles were measured and analyzed. New software for the particle recognition and data analysis of the results obtained from the experiment was developed and used. It has been proven that MASHA + Timepix setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

High intensity vanadium beam for synthesis of new superheavy elements with well-controlled emittance by using "slit triplet".

To provide a very powerful vanadium (V) beam with an intensity of at least 6 particle μA for synthesizing a new superheavy element (SHE) with atomic number Z = 119, we have developed a high-temperature oven (HTO) system to evaporate the metallic V powder inside the new superconducting (SC) electron cyclotron ion source. We successfully extracted a V13+ beam with a maximum beam intensity of 600 eμA with 2.8-kW microwave power and 900-W heating power of the HTO. Furthermore, from a systematic study of the dependence of the beam intensity on the microwave power and the HTO power, we successfully produced a V13+ beam of 300 eμA at a consumption rate of 3 mg/h, allowing a one-month duration continuous beam to carry out the SHE synthesis. In addition, to avoid serious damage to newly introduced SC acceleration cavities by beam losses, the beam should be transported with a well-controlled emittance. To efficiently limit the beam emittance, we employed a slit triplet consisting of three pairs of slits installed around the focus point of the low-energy beam transport. The first result of the emittance reduction was observed by a pepper-pot type emittance meter as a function of the acceptance of the slit triplet.

Calculation of atomic properties of superheavy elements Z=110–112 and their ions

We calculate the spectra, electric dipole transition rates and isotope shifts of the super heavy elements Ds (Z=110), Rg (Z=111) and Cn (Z=112) and their ions. These calculations were performed using a recently developed, efficient version of the ab initio configuration interaction combined with perturbation theory to treat distant effects. The successive ionization potentials of the three elements are also calculated and compared to lighter elements.

Fission of compound nuclei and the developments of microscopic fission theory

Nuclear fission process is a complex large-amplitude dynamic process of quantum many-body systems, and the development of predictive fission descriptions is a well-known challenge in nuclear physics. To describe the fission observables, there are some phenomenological and semi-microscopic models, which rely on adjustments of parameters. The microscopic fission theory based on effective nuclear interactions in principle can avoid free parameters, but they are not ready for accurate applications. This work discussed about the fission of compound nuclei, which is particularly useful for synthesizing superheavy elements. In addition, we discussed the adiabatic and non-adiabatic microscopic fission models. The adiabatic fission model performs better in describing fission observables, while non-adiabatic fission models are valuable to explore fission mechanisms. We discussed the issues and challenges of current fission theories, and realized the fission process is extremely complicated, and some prospects of fission theory have also been discussed.

Stability of the heaviest elements: K isomer in No250

Decay spectroscopy of No250 has been performed using digital electronics and pulse-shape analysis of the fast nuclear decays for the first time. Previous studies of No250 reported two distinct fission decay lifetimes, related to the direct fission of the ground state and to the decay of an isomeric state but without the possibility to determine if the isomeric state decayed directly via fission or via internal electromagnetic transitions to the ground state. The data obtained in the current experiment allowed the puzzle to finally be resolved, attributing the shorter half-life of t1/2=3.8±0.3μs to the ground state and the longer half-life t1/2=34.9−3.2+3.9μs to the decay of an isomeric state. No250 becomes, thus, one of a very few examples of very heavy nuclei with an isomeric state living considerably longer than its ground state. This phenomenon has important consequences for the nuclear-structure models aiming to determine the borders of the island of stability of superheavy elements.

Systematic Study of Quasifission in 48Ca-induced reactions

The production of superheavy elements through the fusion of two heavy nuclei is severely hindered by the quasifission process, which results in the fission of heavy systems before an equilibrated compound nucleus (CN) can be formed. The heaviest elements have been synthesised using 48Ca as the projectile nucleus. However, the use of 48Ca in the formation of new superheavy elements has been exhausted, thus a detailed understanding of the properties that made 48Ca so successful is required. Measurements of mass-angle distributions allow fission fragment mass distribution widths to be determined. The effect of the orientation of prolate deformed target nuclei is presented. Closed shells in the entrance channel are also shown to be more important than the stability of the formed CN in reducing the quasifission component, with reduced mass widths for reactions with the closed shell target nuclei 144Sm and 208Pb. Comparison to mass widths for 48Ti-induced reactions show a significant increase in the mass width compared to 48Ca-induced reactions, highlighting the difficulty faced in forming new superheavy elements using projectiles with higher atomic number than 48Ca.

The role of ion sources in synthesis of the super-heavy elements.

Since the early 1970s, attempts to synthesize Super Heavy Elements (SHE) have been made in many laboratories around the world. One of the main requirements of these experiments is a sufficiently large dose of target irradiation, which should be increased with a decrease in the reaction cross section. In this regard, the capacities of ion sources play an important role for the successful synthesis of SHE. At the FLNR JINR, the discovery and investigation of the new region of super heavy nuclei were based on fusion reactions of 48Ca with 238U-249Cf target nuclei. In these experiments, a technique for the production of metallic 48Ca was developed. The operation mode of the ECR ion source was set to optimize the intensity of 48Ca ions and attain maximum ionization efficiency. Because of the heaviest target for experiments on synthesis of SHE in heavy ion reactions is 249Cf, so further progress in the synthesis of elements with Z > 118 requires the production of intense beams of accelerated neutron enriched isotopes, such as 50Ti, 58Fe, and 64Ni.

First acceleration of heavy ion beams with a superconducting continuous wave HIM/GSI CW-linac

In the future a new superconducting (sc) continuous wave (cw) high intensity heavy ion Linac should provide ion beams with a max. beam energy above the coulomb barrier for the Super Heavy Element (SHE) program at GSI Helmholtzzentrum für Schwerionenforschung. Key features of this new Linac are the acceleration of different ions from protons to uranium as well as a smooth energy variation from 3.5 to 7.3 MeV/u for design ions with a mass-to-charge ratio A/q = 6 and even above for lighter ions. As a first step a newly developed superconducting 15-gap Crossbar H-cavity (CH-cavity) operated at 217 MHz has been successfully tested with heavy ion beam up to the design beam energy of 1.85 MeV/u for the first time. The design energy gain of 3.5 MV within a length of less than 70 cm has been validated with heavy ion beams of up to 1.5 pμA. The measured beam parameters showed excellent beam quality, while a dedicated beam dynamics layout provides beam energy variation between 1.2 and 2.2 MeV/u. The beam commissioning is a milestone of the R&D work of Helmholtz Institute Mainz (HIM) and GSI in collaboration with Goethe University Frankfurt (GUF) and the first step towards a sc heavy ion cw-Linac with variable beam energy. The first tests under cryogenic conditions of the next two CH-cavities have already been started at GUF in a vertical cryostat. The results of the first successful heavy ion beam acceleration with a superconducting CH-cavity will be presented.

Competition between alpha and heavy cluster decay in superheavy element 296Og

Systematic study of superheavy nuclei 296 Og and its possibilities to emit alpha particle and heavier clusters are studied using Modified Generalized Liquid Drop Model (MGLDM) with Q value dependent preformation factor. Half-lives and branching ratio of all possible cluster emission of 296 Og is checked and only those cluster which are within the experimental half-lives limit (less than 10 30 s) and branching ratio limit (down to 10 -19 ) are considered. Among this, 88 Kr is found to be the most probable heavy cluster, leading to doubly magic 208 Pb daughter nuclei, with half-lives comparable with alpha decay half-lives. Thus the role of doubly magic daughter nuclei in cluster decay is highlighted here. Again the decay modes of 296 Og are also studied by comparing alpha decay half-lives using MGLDM with spontaneous fission half-lives proposed by Bao et al. , and from this, it is found that for superheavy element 296 Og, decays by 3 alpha chains followed by spontaneous fission. We hope that this study would help when this emission is experimentally detected in near future.

Cl, K and Ni induced reactions to synthesis SHN 273Rg

We have studied chlorine (Cl), potassium (K) and Nickel (Ni) induced reactions in the synthesis of 273 Rg. We have studied the compound nucleus formation probability, survival probability and evaporation residue cross sections to synthesize superheavy element (SHN) 273 Rg. The selected projectile-target combinations to synthesis 273 Rg are 35,37 Cl + 238,236 Pu, 39-41 K + 234-232 U and 63,64 Ni + 210,209 Bi. From the study of P CN , P sur and σ evr we have identified that 35 Cl+ 238 Pu is the most suitable projectile-target combination to synthesize 273 Rg. We have also compared the present work with the experimental values available in literature.

Evaporation residue cross section to synthesize superheavy element Z=119

The evaporation-residue cross section σEVR of fusion reactions depend on the projectile-target combinations and the incident energy. A detail theoretical study is useful before the synthesis of more isotopes of super heavy nuclei Z=119. We have studied the evaporation-residue cross sections for possible projectile-target combinations to synthesis the superheavy nuclei with Z=119. We have studied the dependence of evaporation residue cross section with that of mass number of the target, product of atomic numbers of projectile and target (Z1Z2), fusion barrier height (Vb) and fusion barrier width (Rb). After the detailed analysis, we have identified the most probable projectile-target combinations. The identified projectile-target combinations to synthesis superheavy nuclei 295-296119 are 45Sc+250,251Cf. We hope that our predictions guide the future experiments in the synthesis of super heavy nuclei 295-296119.

Subbarrier fusion reactions of an aligned deformed nucleus

We discuss heavy-ion fusion reactions of a well-deformed odd-mass nucleus at energies around the Coulomb barrier. To this end, we consider the $^{16}$O+$^{165}$Ho reaction and take into account the effect of deformation of $^{165}$Ho using the orientation average formula. We show that fusion cross sections are sensitive to magnetic substates of the target nucleus, and cross sections for the side collision, which are relevant to a synthesis of superheavy elements, may be enhanced by a factor of around two by aligning the deformed target nuclei. We also discuss the effect of alignment on the fusion barrier distribution. We find that, for a particular choice of alignment, the shape of barrier distribution becomes similar to a typical shape of barrier distribution for a deformed nucleus with a negative hexadecapole deformation parameter, $\beta_4$, even if the intrinsic $\beta_4$ is positive in the target nucleus.

150 years since the development of the Periodic System of Chemical Elements by D.I. Mendeleev

The year 2019 has been declared by UNESCO as the year of the Periodic Table of Elements. 150 years ago, an outstanding Russian scientist D.I. Mendeleev systematized the chemical elements known at that time by chemical properties and created a table of elements. Since then, almost 60 chemical elements have been added to those known 150 years ago. Now the table has 118 chemical elements, most of which were synthesized artificially, in particular, on charged particle accelerators. Especially vigorous growth in the synthesis and research of new heavy transfermium elements was observed during the last 20 years, when about 20 new heavy and super heavy elements were synthesized in various world research centers with powerful accelerator complexes. In the present article, the authors discuss the current situation in the synthesis of new elements with an atomic number greater than 110 and the prospects for further advancement in the region of super heavy elements.