48Ca Ions Research Articles

Manifestation of relativistic effects in the chemical properties of nihonium and moscovium revealed by gas chromatography studies.

Chemical reactivity of the superheavy elements nihonium (Nh, element 113) and moscovium (Mc, element 115) has been studied by the gas-solid chromatography method using a new combined chromatography and detection setup. The Mc isotope, 288Mc, was produced in the nuclear fusion reaction of 48Ca ions with 243Am targets at the GSI Helmholtzzentrum Darmstadt, Germany. After isolating 288Mc ions in the gas-filled separator TASCA, adsorption of 288Mc and its decay product 284Nh on silicon oxide and gold surfaces was investigated. As a result of this work, the values of the adsorption enthalpy of Nh and Mc on the silicon oxide surface were determined for the first time, kJ/mol and kJ/mol (68% c.i.). The obtained -ΔH ads values are in good agreement with results of advanced relativistic calculations. Both elements, Nh and Mc, were shown to interact more weakly with the silicon oxide surface than their lighter homologues Tl and Bi, respectively. However, Nh and Mc turned out to be more reactive than the neighbouring closed-shell and quasi-closed-shell elements copernicium (Cn, element 112) and flerovium (Fl, element 114), respectively. The established trend is explained by the influence of strong relativistic effects on the valence atomic orbitals of these elements.

Fabrication, swift heavy ion irradiation, and damage analysis of lanthanide targets

Abstract One limiting factor in progress in the discovery and study of new superheavy elements (SHE) is the maximum achievable thickness and irradiation stability of current generation actinide targets. The desired thickness of targets, using full excitation function widths, cannot be achieved with current target technology, especially the widely used molecular plating (MP). The aim of this study was to transfer progress in the electrochemistry of lanthanides and actinides to the production of targets. Here, we report on the production of lanthanide targets using anhydrous electrochemical routes. In a first irradiation series, thulium thin films with areal densities up to 1800 μg/cm2 were produced using anhydrous triflate compounds and subjected to irradiation tests, using 6.0 MeV/u 48Ca ions at a fluence of 3.9 × 1014 ions/cm2 and 8.6 MeV/u 197Au ions at fluences in the range of 3.0 × 1011 to 1.0 × 1013 ions/cm2. The thin films were characterised before and after the irradiations using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).

Emission of high-energy alpha particles in nuclear reactions of 48Ca and 56Fe ions on 181Ta and 238U targets

The results of experiments on measuring the energy spectra of alpha particles in reactions with heavy ions are presented. The measurements were performed using the high-resolution magnetic analyzer MAVR with beams of 48Ca (280 MeV) and 56Fe (320 and 400 MeV) on 181Ta and 238U targets at an angle of 0°. A strong dependence of the double differential cross sections for production of alpha particles on the atomic number of the target nucleus was observed, which indicates that fast alpha particles are mainly emitted from the target nucleus; this conclusion was also confirmed by calculations within the time-dependent Schrödinger equation approach. An analysis of the obtained experimental data was carried out within the model of moving sources modified to consider the kinematic limits for two-body and three-body exit channels.

Light Spectral Composition Influences Structural and Eco-Physiological Traits of Solanum lycopersicum L. cv. ‘Microtom’ in Response to High-LET Ionizing Radiation

This study evaluated if specific light quality (LQ) regimes (white fluorescent, FL; full-spectrum, FS; red-blue, RB) during plant growth modified morphological and photosynthetic traits of Solanum lycopersicum L. ‘Microtom’ plants irradiated at the dry seed stage with 25 Gy 48Ca ions (IR). The irradiation reduced plant size while it increased leaf dry matter content (LDMC) and relative water content (RWC) compared to the control. FS and RB light regimes determined a decrease of plant height and a rise of RWC compared to FL plants. The irradiation under FS and RB regimes favoured the development of dwarf plants and improved the leaf water status. Under the FL regime, irradiated plants showed reduced photosynthesis and stomatal conductance. The opposite behavior was observed in RB irradiated plants in which gas exchanges were significantly stimulated. RB regime enhanced Rubisco expression in irradiated plants also inducing anatomical and functional adjustments (i.e., increase of leaf thickness and incidence of intercellular spaces). Finally, 48Ca ions did not prevent fruit ripening and the achievement of the ‘seed-to seed’ cycle, irrespective of the LQ regime. Overall, the present study evidenced that RB light regime was the most effective in optimising growth and photosynthetic efficiency of ‘Microtom’ irradiated plants. These outcomes may help to develop proper cultivation protocols for the growth of dwarf tomato in Controlled Ecological Life Support Systems (CELSS).

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.

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.

Superheavy elements

Synthesis of superheavy elements predicted by microscopic nuclear theory is investigated. The heaviest elements with Z = 114–118 were synthesized by fusion reactions of actinide nuclei with 48Ca ions accelerated using the U-400 complex at the Flerov Laboratory of Nuclear Reactions (FLNR), one of seven laboratories that comprise the Joint Institute for Nuclear Research (JINR) located in Dubna, Russia. The experiments were carried out in collaboration with physicists and chemists working at the Livermore and Oak Ridge national laboratories in located in California and Tennessee, respectively. Discovery of these elements allowed completion of the seventh period of the periodic table. The microscopic nuclear theory’s fundamental predictions about the possible existence of superheavy elements received the experimental confirmation. A new laboratory, i.e., the "STE Factory" associated with the JINR FLNR, has been established to research superheavy nuclei.

Measurement of the Production Cross Sections for Isotopes of Transfermium Elements in Complete Fusion Reactions with the Subsequent Evaporation of a Proton and Neutrons

Experiments aimed at synthesizing and investigating the features of radioactive decay of isotopes of superheavy elements (Z ≥ 110) have been conducted in the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. Complete fusion reactions of an accelerated beam of 48Ca ions with transactinide targets with the subsequent evaporation of several neutrons from excited compound nucleus are typically used in these experiments. “Exotic” reaction channels with the evaporation of protons and several neutrons may be used to produce more neutron-rich isotopes of superheavy elements. The production cross sections were measured in experiments at the SHELS separator for Db and Rf isotopes produced in xn and pxn channels of the 50Ti + 209Bi → 259Db* reaction. The ratio of cross sections σ(xn)/σ(pxn) was on the order of 100.

Experimental Investigation of the Joint Influence of Reduced Supply Voltage and Charge Sharing on Single-Event Transient Waveforms in 65-nm Triple-Well CMOS

Full waveforms of single-event transients (SETs) in inverter chains were measured under focused heavy-ion microbeam irradiation. Inverter chains of varying spacings were irradiated with 48Ca and 197Au ions. The influence of changing the supply voltage from subthreshold to nominal level on SET forming and propagation was investigated, and the role of charge sharing is discussed. Key factors that influence SET widths and cross sections are identified across the applied range of supply voltages. A simple method is presented for estimating average SET widths at decreased supply voltages, and is based on the SET width measurements at nominal supply voltage, transistor-level simulations, and extracted circuit parameters. The proposed method matches well with the measured data.

مطالعه سنتز برخی از ایزوتوپهای هسته فلروویوم Fl، واقع در جزیره پایداری و مقایسه پارامترهای سد همجوشی آنها

In the present research, we want to study synthesis of some isotopes of Flerovium ، ، and were produced in the nuclear fusion of 48Ca ions with 239Pu, 240Pu, 241Pu, and 242Pu nuclei. We obtain the parameters of the fusion barriers between48Ca ions with Pu isotopes and compare these parameters with each other. Furthermore, we investigate influence of the direction of target nuclei on the parameters of the fusion barriers. we show that the minimum energies for synthesis of 287Fl, 288Fl, 289Fl and 290Fl nuclei are 184.16 MeV, 183.95 MeV, 183.75 MeV and 183.56 MeV. Finally in the framework of the statistical model, we estimate the evaporation residue cross section for 286Fl, 287Fl nuclei after emission of three and four neutrons from 290Fl nuclei and we will show that the results of calculations for 286Fl nuclei are in good agreement with the experimental data. Although, the results of the calculations of the evaporation residue cross section for 287Fl nuclei lie somewhat below the results of the experimental data.

Study of the 249-251Cf + 48Ca reactions: recent results and outlook

Experiment aiming at the synthesis of heavy isotopes of Z=118 (Og) using beam of 48Ca and a target of 249-251Cf was undertaken in October 2015 – April 2016 employing the Dubna Gas-Filled Recoil Separator (FLNR JINR). The target of mixed isotopes of 249-251Cf (50.7% of 249Cf, 12.9% of 250Cf, and 36.4% of 251Cf) was irradiated by 48Ca ions at two beam energies of 252 and 258 MeV with the corresponding accumulated beam doses of 1.6×1019 and 1.1×1019. A single event observed at lower beam energy was assigned to the isotope 294Og, the product of the reaction 249Cf(48Ca, 3n); its decay pattern and the observed radioactive properties of the nuclides in the decay chain reproduce in full those observed for 294Og in our earlier experiments of 2002-2005 and 2012. At higher beam energy we observed no decay chains that could be attributed to the isotopes of Og. The possibility of renewal of this experiment in the future is discussed.

Reexamination of the Claim of Marinov <i>et al.</i> on Discovery of Element 112

Marinov et al. have detected spontaneous fission events in sources separated from tungsten targets irradiated with 24 GeV protons. These fission events could not be attributed to actinides or to any other known isotope. Marinov et al. propose that fission events are due to production of element 112 (Eka-Hg) in the tungsten target. We have addressed Marinov’s claim with a new analysis of their data and modern theoretical model calculations of possible interactions. Using data available in the literature the spontaneous fission half-life of the Eka-Hg was estimated to be ～74 days. This is dramatically longer than the half-life obtained for 283112Cn, produced in the fusion of energetic 48Ca ions with 238U. Monte Carlo calculations show that enough Sr isotopes are produced in the tungsten target to make the production of element 112 via fusion of Sr and W feasible; however, if such fusion was possible it had to be deep sub-barrier fusion.

Separator for Heavy ELement Spectroscopy – velocity filter SHELS

The SHELS velocity filter originated upon reconstruction of the VASSILISSA electrostatic separator used for investigations of heavy nuclei produced in complete fusion reactions. The goals of this modernization were to increase the transmission of products of asymmetric reactions and to extend the region of reactions to be investigated up to symmetric combinations. The first tests of the set-up were performed with the beams of accelerated 22Ne, 40Ar, 48Ca, and 50Ti ions.

Production and decay of the heaviest odd-Z nuclei in the 249Bk + 48Ca reaction

The reaction of 249Bk with 48Ca has been investigated with an aim of synthesizing and studying the decay properties of isotopes of the new element 117. The experiments were performed at five projectile energies (in two runs, in 2009-2010 and 2012) and with a total beam dose of 48Ca ions of about 9x1019 The experiments yielded data on a-decay characteristics and excitation functions of the produced nuclei that establish these to be 293117 and 294117 – the products of the 4n- and 3n-evaporation channels, respectively. In total, we have observed 20 decay chains of Z=117 nuclides. The cross sections were measured to be 1.1 pb for the 3n and 2.4 pb for the 4n-reaction channel. The new 289115 events, populated by α decay of 117, demonstrate the same decay properties as those observed for 115 produced in the 243Am(48Ca,2n) reaction thus providing cross-bombardment evidence. In addition, a single decay of 294118 was observed from the reaction with 249Cf – a result of the in-growth of 249Cf in the 249Bk target. The observed decay chain of 294118 is in good agreement with decay properties obtained in 2002-2005 in the experiments with the reaction 249Cf(48Ca,3n)294118. The energies and half-lives of the odd-Z isotopes observed in the 117 decay chains together with the results obtained for lower-Z superheavy nuclei demonstrate enhancement of nuclear stability with increasing neutron number towards the predicted new magic number N=184.

Elements of experiment automation on the Dubna gas-filled recoil nuclei separator plant

Schematics, software products, and their realization in a Builder C++ environment for experiments on the synthesis of superheavy elements on a Dubna gas-filled recoil nuclei separator (DGFNS) plant at the Flerov Laboratory of Nuclear Reactions (FLNR) of the Joint Institute for Nuclear Research (JINR) are considered. Examples of application in complete fusion reactions with 48Ca ions are given.

Synthesis of new superheavy elements using the Dubna Gas-Filled Separator: The complex of technologies

All the new isotopes of superheavy elements in the reactions with 48Ca ions and actinide targets, synthesized at the Flerov Laboratory of Nuclear Reactions (FLNR), have been obtained at the Dubna Gas-Filled Recoil Separator (DGFRS). Success was achieved with the use of several techniques, algorithms and approaches with record performance in their area. The most sophisticated of them are rare event detection technology, methods of measuring the effective equilibrium charges of heavy ions and nuclei in hydrogen at low pressure, modified approaches to evaluation of probabilistic characteristics of detected multichain events, beam-free test methods of detection equipment, and some other ones. The author analyzes the approaches that have led ultimately to a real breakthrough and an advance in experiments on the synthesis of superheavy elements. The development of detection systems also attracts the authors’ attention. Contributions from some facilities—such as SHIP, TASCA, and GARIS (RIKEN)—to synthesis experiments are partially noted. Under consideration are methods of automation of similar experiments, including the development of control and shielding systems for operation with highly active actinide targets. Some techniques for detecting α decay of heavy nuclei that came before the current experiments with electromagnetic separators are reviewed briefly. The methods, algorithms and hardware presented cover a more than twenty-year period of commissioning and application in long-term experiments at FLNR DGFRS.

The time scale of quasifission process in reactions with heavy ions

The study of mass-energy distributions of binary fragments obtained in the reactions of 36S, 48Ca, 58Fe and 64Ni ions with the 232Th, 238U, 244Pu and 248Cm at energies below and above the Coulomb barrier is presented. These data have been measured by two time-of-flight CORSET spectrometer. The mass resolution of the spectrometer for these measurements was about 3u. It allows to investigate the features of mass distributions with good accuracy. The properties of mass and TKE of QF fragments in dependence on interaction energy have been investigated and compared with characteristics of the fusion-fission process. To describe the quasifission mass distribution the simple method has been proposed. This method is based on the driving potential of the system and time dependent mass drift. This procedure allows to estimate QF time scale from the measured mass distributions. It has been found that the QF time exponentially decreases when the reaction Coulomb factor Z1Z2 increases.

The dubna gas-filled recoil separator: Software and algorithms

Experiments carried out on the gas-filled separator of recoil nuclei at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, in the past several years have proved the hypothesis of the existence of a stability island of superheavy nuclei. The accelerator, beam diagnostics, and detector technologies underlay the success. It is the highly sensitive detecting system of the separator combined with the method of “active correlations” that allowed rare events of the decay of superheavy nuclei to be reliably detected under almost background-free conditions. In turn, to a large extent, this has been made possible owing to special algorithms and software developed for long-term experiments in the beam of 48Ca ions.

Symmetric and asymmetric quasifission in reactions with heavy ions

The main aim of the present study is to evaluate the fusion probabilities and investigate competing quasifission process in the reactions with heavy ions leading to the formation of superheavy composite systems. The mass-energy distributions of binary fragments as well as their cross sections have been measured for a wide range of composite systems with Z=82–122 formed in the reactions with 22Ne, 26Mg, 48Ca, 58Fe and 86Kr ions at energies around the Coulomb barrier. The experiments were carried out using a double-arm time-of-flight spectrometer of binary reaction products CORSET. The results of the experimental investigation of the influence of the entrance channel properties on the competition between fusion-fission and quasifission for the "warm" fusion reactions is discussed.

Attenuation of ambient dose equivalent from neutrons by thick concrete, cast iron and composite shields for high energy proton, 3He, 48Ca and 238U ions on Cu targets for shielding design

Data on neutron dose attenuation by thick concrete, cast iron, and cast iron plus concrete composite shields for heavy ions and protons having high energies (200–1000 MeV/u) are necessary for shielding designs of high-powered heavy ion accelerator facilities. Neutron production source terms, shield material attenuation lengths, and neutron dose rate reduction effectiveness of the bulk shielding in the angular range from 0° to 125° were determined by the Particle and Heavy Ion Transport Code (PHITS) for beams of 300 and 550 MeV/u 48Ca ions, 200 and 400 MeV/u 238U ions, 800 MeV/u 3He and 1 GeV protons. Calculated results of interaction lengths of concrete and cast iron were also compared with similar work performed by Agosteo et al., and to experimental and other calculated data on interaction lengths. The agreement can be regarded as acceptable.