Gas-filled Separator Research Articles

Toward the Discovery of New Elements: Production of Livermorium (Z=116) with ^{50}Ti.

The ^{244}Pu(^{50}Ti,xn)^{294-x}Lv reaction was investigated at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. The experiment was aimed at the production of a superheavy element with Z≥114 by irradiating an actinide target with a beam heavier than ^{48}Ca. Produced Lv ions were separated from the unwanted beam and nuclear reaction products using the Berkeley Gas-filled Separator and implanted into a newly commissioned focal-plane detector system. Two decay chains were observed and assigned to the decay of ^{290}Lv. The production cross section was measured to be σ_{prod}=0.44(_{-0.28}^{+0.58}) pb at a center-of-target center-of-mass energy of 220(3)MeV. This represents the first published measurement of the production of a superheavy element near the "island of stability," with a beam of ^{50}Ti and is an essential precursor in the pursuit of searching for new elements beyond Z=118.

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.

Study of the 242Pu + 48Ca Reaction at Super Heavy Element Factory

Experiments on the synthesis of isotopes of element 114 in the 242Pu + 48Ca reaction were carried out at a new gas-filled separator DGFRS-2 online to the DC-280 cyclotron of the Superheavy Element Factory at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. The decay properties of 286Fl and 287Fl, as well as their α-decay products, were refined. The possibility of the existence of isomeric states in successive α-decays of 287Fl is discussed. The maximum cross section of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10.4_{{ - 2.1}}^{{ + 3.5}}$$\\end{document} pb was measured for the 242Pu(48Ca, 3n)287Fl reaction.

First Tests of the GRAND Gas-Filled Separator at the Superheavy Element Factory (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research)

First Tests of the GRAND Gas-Filled Separator at the Superheavy Element Factory (Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research)

Study of the <sup>242</sup>Pu + <sup>48</sup>Ca reaction at Super Heavy Element Factory

Experiments on the synthesis of isotopes of element 114 in the 242Pu + 48Ca reaction were carried out at a new gas-filled separator DGFRS-2 online to the DC-280 cyclotron of the Superheavy Element Factory at FLNR JINR. The decay properties of 286Fl and 287Fl, as well as their α-decay products, were refined. The possibility of the existence of isomeric states in successive α-decays of 287Fl is discussed. The maximum cross section of \(10.4_{{ - 2.1}}^{{ + 3.5}}\) pb was measured for the 242Pu(48Ca, 3n)287Fl reaction.

Magnetic System of the Gas-Filled Separator GASSOL for Studying Properties of Superheavy Elements

Magnetic System of the Gas-Filled Separator GASSOL for Studying Properties of Superheavy Elements

Segmented silicon-based solid-state detector with thin dead layer for superheavy element research

Silicon-based solid-state detectors (SSDs) are crucial for investigating the properties of superheavy elements (SHEs), since they measure the energy of SHEs and charged particles that are emitted as successive decay events of the SHEs. We have developed a segmented SSD for SHE studies using the new gas-filled recoil ion separators (GARIS-II and GARIS-III) at RIKEN. It is based on a back-illuminated Si PIN photodiode in which the irradiation is through the N+ layer. The detector is introduced as a side one for the GARIS focal plane detection system. To investigate the characteristics of the SSD, 241Am α particles were irradiated by automatically moving and rotating the α source for each segmented portion of the SSD. A Monte Carlo simulation was also performed to estimate the dead layer thickness of the segmented SSD.

Spectroscopy along flerovium decay chains. III. Details on experiment, analysis, Cn282 , and spontaneous fission branches

Flerovium isotopes (element Z=114) were produced in the fusion-evaporation reactions Ca48+Pu242,244 and studied with an upgraded TASISpec decay station placed in the focal plane of the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Twenty-nine flerovium decay chains were identified by means of correlated implantation, α decay, and spontaneous fission events. Data analysis aspects and statistical assessments, primarily based on measured rates of various events, which laid the foundation for the comprehensive spectroscopic information on the flerovium decay chains, are presented in detail. Various decay scenarios of an excited state observed in Cn282 are examined in depth with the help of Geant4 simulations and assessed by predictions of beyond mean-field calculations including triaxial shape degrees of freedom. Previous, revised, and newly derived fission probabilities of even-even superheavy nuclei are compared with various theoretical predictions.Received 12 April 2022Revised 19 December 2022Accepted 4 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.024301Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayFissionNuclear structure & decaysNuclear Physics

Decay spectroscopy of Os171,172 and Ir171,172,174

We report on a study of the α-decay fine structure and the associated Eα−Eγ correlations in the decays of Os171,172 and Ir171,172,174. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to Re168 and W167. The weak α-decay branch from the bandhead of the νi13/2 band in Os171 observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus Os171 is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in Mo92(Kr83,xpyn) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of detectors for charged particles and electromagnetic radiation known as GREAT. Prompt γ-ray transitions were detected and correlated with the decays using the JUROGAM II germanium detector array surrounding the target position. Results obtained from total Routhian surface (TRS) calculations suggest that α-decay fine structure and the associated hindrance factors may be a sensitive probe of even relatively small shape changes between the final states in the daughter nucleus.5 MoreReceived 13 October 2022Accepted 11 January 2023DOI:https://doi.org/10.1103/PhysRevC.107.014308Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayLow & intermediate energy heavy-ion reactionsNuclear structure & decaysProperties150 ≤ A ≤ 189Nuclear Physics

Facility upgrade for superheavy-element research at RIKEN

The RIKEN Nishina Center (RNC) executed an accelerator upgrade project for the heavy-ion linac (called RILAC). A superconducting RIKEN linear accelerator (SRILAC) and a new superconducting electron-cyclotron-resonance ion source (SC-ECRIS) to boost the final energy and intensity were constructed, aimed at synthesizing a new superheavy element, 119, through a hot fusion reaction. The project included the construction of a gas-filled recoil ion separator (GARIS-III) suitable for detecting the residues of the hot-fusion reaction. To avoid research interruption during the SRILAC construction period (2017–2019) and gain experience in hot-fusion reaction processes, GARIS-II located in the GARIS experimental hall in LINAC building was moved to the E6 experimental hall in Nishina building. Certain exploratory measurements were performed employing the beams accelerated by RILAC2 and the RIKEN ring cyclotron (RRC), which is a part of the existing accelerator complex of the radioactive isotope beam factory (RIBF). Further, commissioning experiments with the upgraded facility (SRILAC and GARIS-III) were performed. The upgrade project and its commissioning results are chronologically described in this article.

New isotope Mc286 produced in the Am243+Ca48 reaction

In this paper, we present results of the second experiment on the synthesis of Mc isotopes in the Am243+Ca48 reaction performed at the gas-filled separator DGFRS-2 of the SHE Factory at JINR. The new isotope Mc286 was synthesized, and its half-life of 20+98−9 ms and α-particle energy of 10.71±0.02 MeV were determined. A Mc286 α−decay chain was recorded down to the spontaneous fission of Db266. The spontaneous fission of Rg279 was observed for the first time in one of four new decay chains of Mc287. The excitation function of the reaction was measured at three Ca48 energies of 242, 250, and 259 MeV; the latter resulted in the first observation of the 5n−evaporation channel with a cross section of 0.5−0.4+1.3 pb. The decay properties of 21 previously known odd−Z isotopes were improved. The potential for an electron-capture decay mode is discussed for Mc288 and Nh284 isotopes. The half-lives of spontaneously fissioning nuclei produced in the Ca48−induced reactions with actinide targets are compared with several theoretical predictions.Received 10 October 2022Accepted 22 November 2022DOI:https://doi.org/10.1103/PhysRevC.106.064306©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayBeta decayFissionLow & intermediate energy heavy-ion reactionsNuclear fusionNuclear reactionsNuclear structure & decaysRare & new isotopesPropertiesA ≥ 220TechniquesSpectrometers & spectroscopic techniquesNuclear Physics

Investigation of Ca48 -induced reactions with Pu242 and U238 targets at the JINR Superheavy Element Factory

Experiments using a Ca48 beam on U238 and Pu242 targets to produce superheavy nuclei were performed at the gas-filled separator DGFRS-2 online to the new cyclotron DC280 at the SHE Factory at JINR. The decay properties of Fl286 and Fl287, as well as their α-decay products, were refined after the detection of 25 and 69 new decay chains, respectively. In addition, 16 decay chains of Cn283 were observed in the U238+Ca48 reaction. The possibility of existing of isomeric states in the Fl287 consecutive α decays is discussed. A new α line with an energy of 100–200 keV lower than the main one at 10.19 MeV was observed for the first time for even-even Fl286 decay. A maximum cross section of 10.4−2.1+3.5pb was measured for the Pu242(Ca48,3n) Fl287 reaction.Received 25 May 2022Accepted 1 August 2022DOI:https://doi.org/10.1103/PhysRevC.106.024612©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayFissionIsomer decaysNuclear fusionPropertiesA ≥ 220Nuclear Physics

DGFRS-2—A gas-filled recoil separator for the Dubna Super Heavy Element Factory

The main goal of development of the new Dubna Gas-Filled Recoil Separator (DGFRS-2) is to sufficiently improve the efficiency of studies on heavy and superheavy nuclei at the Super Heavy Element Factory of the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research. The use of beams with the intensity up to 6×1013 s−1 (10 pμA) delivered by the DC280 cyclotron requires an effective setup providing high suppression of background reaction products. The described gas-filled separator is optimized for synthesis and study of heavy isotopes produced in complete fusion reactions of massive nuclei. Basic characteristics of DGFRS-2, as well as the results of the first test experiments, are presented. In comparison to the DGFRS-1, the transmission efficiency was doubled, and the background was reduced by a factor 200.

α -decay-correlated mass measurement of Ra206,207g,m using an α -TOF detector equipped multireflection time-of-flight mass spectrograph system

The atomic masses of the isotopes Ra206,207 have been measured via decay-correlated mass spectroscopy using a multireflection time-of-flight mass spectrograph equipped with an α-TOF detector. The Ra isotopes were produced as fusion-evaporation products in the V51+Tb159 reaction system and delivered by the gas-filled recoil ion separator GARIS-II at RIKEN. The α-TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent α-decay events. The masses of Ra206 and Ra207g,m were directly measured using a multireflection time-of-flight mass spectrograph equipped with an α-TOF detector. The mass excesses of Ra206,207g and the excitation energy of Ra207m were determined to be ME=3540(50)keV/c2, 3538(15)keV/c2, and Eex=552(42) keV, respectively. The α-decay branching ratio of Ra207m, bα=0.26(20), was directly determined from decay-correlated time-of-flight signals, and the reduced α width of Ra207m was calculated to be δ2=43−34+68 keV from the branching ratio. The spin-parity of Ra207m was confirmed to be Jπ=13/2+ from decay correlated mass measurement results.1 MoreReceived 20 June 2021Accepted 28 September 2021Corrected 29 October 2021DOI:https://doi.org/10.1103/PhysRevC.104.044617©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAlpha decayBinding energy & massesNuclear reactionsProperties190 ≤ A ≤ 219Nuclear Physics

First high-precision direct determination of the atomic mass of a superheavy nuclide

We present the first direct measurement of the atomic mass of a superheavy nuclide. Atoms of Db257 (Z=105) were produced online at the RIKEN Nishina Center for Accelerator-Based Science using the fusion-evaporation reaction Pb208(V51, 2n)Db257. The gas-filled recoil ion separator GARIS-II was used to suppress both the unreacted primary beam and some transfer products, prior to delivering the energetic beam of Db257 ions to a helium gas-filled ion stopping cell wherein they were thermalized. Thermalized Db3+257 ions were then transferred to a multireflection time-of-flight mass spectrograph for mass analysis. An alpha particle detector embedded in the ion time-of-flight detector allowed disambiguation of the rare Db3+257 time-of-flight detection events from background by means of correlation with characteristic α decays. The extreme sensitivity of this technique allowed a precision atomic mass determination from 11 events. The mass excess was determined to be 100063(231)stat(132)syskeV/c2. Comparing to several mass models, we show the technique can be used to unambiguously determine the atomic number as Z=105 and should allow similar evaluations for heavier species in future work.Received 4 June 2020Revised 3 March 2021Accepted 30 July 2021DOI:https://doi.org/10.1103/PhysRevC.104.L021304©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBinding energy & massesNuclear fusionPropertiesA ≥ 220MassNuclear mass rangesTechniquesAtom & ion trapping & guidingMass spectrometryTime-of-flight mass spectrometryNuclear Physics

Empirical relations for heavy-ion equilibrated charges and charge-changing cross sections in diluted $$\hbox {H}_{{2}}$$ with application

Highly ionized heavy evaporation residues (ERs) resulting from heavy-ion (HI) fusion–evaporation reactions are knocked out from solid targets to rarefied gas of gas-filled recoil separators. In gas, these ERs undergo charge-changing collisions on their way to a detection system. An equilibrium between the loss of charge (electron capture) and the gain of charge (electron loss) for ionized ERs allows one to use equilibrated charge-state distributions in trajectory calculations for ERs moving through a magnetic field. The distance from a target to the point where the ER charge-state distributions become to be the equilibrated one is essential for such calculations. This distance can be estimated in simulations based on electron capture and loss cross sections for energetic HIs. Reasonable approximations of available experimental data have provided these cross sections, which were applied to the Monte Carlo simulations of the ionic charge evolution for highly ionized heavy ERs. The results of these simulations demonstrate the setting of charge equilibration close to the target.

Identification of sub- μs isomeric states in the odd-odd nucleus Au178

The neutron-deficient gold (Z=79) isotopes in the vicinity of the neutron midshell N=104 provide prolific examples of shape coexistence and isomerism at low excitation energy. They can be probed via a number of different experimental techniques. In this study, two new isomeric states with half-lives of 294(7) and 373(9) ns have been observed in the neutron-deficient odd-odd nuclide Au178 (N=99) in an experiment at the RITU gas-filled separator at JYFL, Jyvaskyla. This result was achieved due to the use of a segmented planar germanium detector with a high efficiency at low energies. By applying the recoil-decay tagging technique, they were assigned to decay to two different long-lived α-decaying states in Au178.

Spectroscopy along Flerovium Decay Chains: Discovery of ^{280}Ds and an Excited State in ^{282}Cn.

A nuclear spectroscopy experiment was conducted to study α-decay chains stemming from isotopes of flerovium (element Z=114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ^{48}Ca+^{242}Pu and ^{48}Ca+^{244}Pu provided a total of 32 flerovium-candidate decay chains, of which two and eleven were firmly assigned to ^{286}Fl and ^{288}Fl, respectively. A prompt coincidence between a 9.60(1)-MeV α particle event and a 0.36(1)-MeV conversion electron marked the first observation of an excited state in an even-even isotope of the heaviest man-made elements, namely ^{282}Cn. Spectroscopy of ^{288}Fl decay chains fixed Q_{α}=10.06(1) MeV. In one case, a Q_{α}=9.46(1)-MeV decay from ^{284}Cn into ^{280}Ds was observed, with ^{280}Ds fissioning after only 518 μs. The impact of these findings, aggregated with existing data on decay chains of ^{286,288}Fl, on the size of an anticipated shell gap at proton number Z=114 is discussed in light of predictions from two beyond-mean-field calculations, which take into account triaxial deformation.

Studying multi-nucleon transfer reaction in a recoil mass spectrometer

We present simulation of a recoil mass spectrometer for measurement of multi-nucleon transfer reactions, based on Monte Carlo techniques. Target-like ions are generated event by event and transported to the focal plane of the spectrometer by the method of transfer matrices. Measured focal plane spectra for the elastic and six transfer channels of the reaction $$^{28}$$ Si+ $$^{94}$$ Zr are reproduced at two projectile energies near the Coulomb barrier. Excellent reproduction is achieved even with first-order ion-optical calculations, indicating not so significant role of higher order aberrations in conventional recoil separators with smaller acceptance. This is in striking contrast with the large acceptance magnetic separators used for studying transfer reactions, for which complex trajectory reconstruction algorithms involving higher order aberrations are essential. Transmission efficiency of the spectrometer, calculated by the reported code, is crucial to convert measured transfer probabilities to differential and integral transfer cross sections for each channel. We show effectiveness of the proposed methodology by extracting differential elastic scattering cross sections from measured yields for the reaction $$^{28}$$ Si+ $$^{94}$$ Zr. Besides being useful for other recoil mass spectrometers, our methodology can be employed for measurement of quasi-elastic reaction cross sections in velocity filters and gas-filled separators.

Reduction of contaminants originating from primary beam by improving the beam stoppers in GARIS-II

Two independent beam stoppers have been developed for improving the beam separation of the gas-filled recoil ion separator GARIS-II. Performance of these supplemental beam stoppers was investigated by using the 208Pb (18O,3n) 223Th reaction. A160-fold enhancement of the signal-to-noise ratio at the GARIS-II focal plane was observed.