U-400 Cyclotron Research Articles

Time-of-flight fission fragment spectrometer of the MAVR facility

A time-of-flight system was created to register the reaction products and perform correlation measurements on a high-resolution magnetic analyzer (MAVR). The facility is located on the channel of the extracted beam of the U-400 cyclotron at the Laboratory of Nuclear Reactions JINR. The results of measuring the parameters of the time-of-flight spectrometer obtained on the basis of measuring the spontaneous fission fragments velocities of 252Cf are described. In addition, the results of the measurement of fission fragments in the 48Ca+238U reaction are presented. In this case, two time-of-flight arms were used, with the help of it is planned to carry out correlation measurements of induced fission fragments of a complex system. The created system also makes it possible to carry out correlation (three particles) measurements of fission fragments with particles registered in the focal plane of the MAVR magnetic spectrometer. Another purpose of the described system is to register elastically scattered ions, which is used as a monitoring system for the quality and composition of the beam hitting on the target of the MAVR facility.

Detailed Study of the Radioactive Decay Properties of No, Rf, and Db Isotopes

Properties of the radioactive decay of No, Rf isotopes are studied in the reaction $^{50}$Ti + $^{209}$Bi → $^{259}$Db* . The cross sections of Db and Rf isotopes production in channels xn and pxn, respectively, are measured. High intensity beams of accelerated heavy ions $^{22}$Ne, $^{48}$Ca, $^{50}$Ti, and $^{54}$Cr of the U400 cyclotron and SHELS kinematic separator are used in the experiments.

Spectroscopy of the Isotopes of Transfermium Elements in Dubna: Current Status and Prospects

A great many experimental studies devoted to exploring in detail the properties of radioactive decay of the isotopes of transfermium elements by means of alpha, beta, and gamma spectroscopy have been performed over the past fifteen years at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research, Dubna). High-intensity accelerated heavy-ion beams of $${}^{22}$$ Ne, $${}^{48}$$ Ca, $${}^{50}$$ Ti, and $${}^{54}$$ Cr from the U-400 cyclotron were used in experiments with the SHELS kinematic separator. An upgrade of the separator and detector system is planned in the future with the aim of improving the transportation efficiency for the nuclei under study and the detection efficiency for gamma rays.

Start-Up of the DC-280 Cyclotron, the Basic Facility of the Factory of Superheavy Elements of the Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research

The basic facility of the Factory of Superheavy Elements (SHE), the DC-280 cyclotron, in the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research has been completed. Both new and experimentally tested engineering solutions of the laboratory underlie the project. Planned beam intensities of up to 10 pμA of ions with average masses (A ~ 50) are one order of magnitude higher than those produced at the U-400 cyclotron up to now. From 2016 to 2018, the DC-280 cyclotron equipment was installation and set up. The first 84Kr14+ ion beam was accelerated in the DC-280 on December 26, 2018, and extracted to the accelerated ion transportation channel on January 17, 2019. In March 2019, beams of accelerated 84Kr+14 ions with an intensity of 1.36 pμA and 12С+2 ions with an intensity of 10 pμA were extracted from the DC-280 to the beam transportation channel with an energy of about 5.8 MeV/nucleon. The main task of the new accelerator is to implement a long-term research program at the SHE Factory aimed at the synthesis of new elements (Z ≥ 119) and a detailed study of nuclear–physical and chemical properties of previously discovered elements nos. 112–118.

Life as an element discoverer, by Julie Ezold

If you had told me 10 years ago that I would be part of an international team of experts who would discover a new element, I would have said, “I don’t think so.” But that is exactly what happened. I am honored to have been part of the discovery of element 117, tennessine. I have been fascinated by the periodic table of the elements since my first chemistry class. The periodic table listed in my advanced chemistry textbook went only to lawrencium (element 103) and identified elements 104–6 as “discovered” but not yet named. Fast-forward to today, and all the elements in the seventh row of the periodic table have been filled in along with their names. To make an element is no small feat. For instance, to make tennessine, we needed to bombard a target made of the isotope berkelium-249 with a beam of calcium-48 ions. The U400 cyclotron

Searching for the Superasymmetric Fission Mode of 248Cf, 254Fm, and 260No in Reactions 22Ne + 232Th, 238U; 16O + 232Th, 238U

The mass and energy distributions of fission fragments in reactions 16O + 232Th, 16O + 238U, 22Ne + 232Th, and 22Ne + 238U are measured to investigate the role of closed proton and neutron shells in the fission of 248Cf, 254Fm, and 260No nuclei at excitation energies of 40–45 MeV. Experiments are performed on the U-400 cyclotron at the Flerov Laboratory of Nuclear Reactions (Dubna, Russia) using the CORSET double-arm time-of-flight spectrometer. For compound nucleus 260No* formed in the reaction 22Ne + 238U, an increase in the fragment yields is observed in the superasymmetric mass region 52/208 amu, which corresponds to the formation of fissioning pairs of two double-magic nuclei, 48Ca and 208Pb. Superasymmetric fission at a mass yield level of 10−5 was not observed for compound nuclei 248Cf and 254Fm* formed in reactions 16O + 232Th, 16O + 238U, and 22Ne + 232Th at an initial excitation energy of 40−45 MeV. Bimodal fission was observed for the 260No*compound nucleus at an initial excitation energy of 41 MeV. In the symmetric mass split, both fission fragments are in this case close to double-magic 132Sn.

Inverse quasifission in the reactions Gd156,160+W186

Background: Low-energy multinucleon transfer reactions may be used for production of new neutron-enriched heavy nuclei.Purpose: Our aim is to investigate the influence of proton ($Z=82$) and neutron ($N=82$, 126) shells as well as orientation effects on the formation of reaction products in the inverse quasifission process in the reactions $^{156,160}\mathrm{Gd}+^{186}\mathrm{W}$.Methods: Mass, energy, and angular distributions of primary binary fragments formed in the reactions $^{156}\mathrm{Gd}+^{186}\mathrm{W}$ at an energy of 878 MeV, and $^{160}\mathrm{Gd}+^{186}\mathrm{W}$ at 860 and 935 MeV, have been measured using the double-arm time-of-flight spectrometer CORSET at the U400 cyclotron of the Flerov Laboratory of Nuclear Reactions (FLNR) at the Joint Institute for Nuclear Research (JINR), Dubna.Results: Enhancement in the yield of products with masses 200--215 u has been found for both reactions. The cross sections of the formation of trans-target fragments with masses around 208 u are found to be about 10 \ensuremath{\mu}b at the Coulomb barrier energy and reach the level of 0.5 mb at the energy above the barrier for side-to-side collision.Conclusions: The enhanced yield of products with masses heavier than the target mass confirms the important role of the closed shells at $Z=82$ and $N=82$, 126 in the inverse quasifission process in low-energy damped collisions. The orientation effect caused by the strong deformation of colliding nuclei can result in a gain in the yield of heavy target-like fragments.

Spontaneous fission of 256Rf, new data

Spontaneous fission properties of the short-lived neutron-deficient 256Rf nucleus produced in the complete fusion reaction with a beam of multiply charged heavy 50Ti ions from the U-400 cyclotron (FLNR, JINR) are experimentally investigated. Its half-life and decay branching ratio are measured. The average number of neutrons per spontaneous fission of 256Rf (\(\bar v = \;4.47 \pm \;0.09\)) is determined for the first time.

Study of neutron-deficient isotopes of Fl in the 239Pu, 240Pu + 48Ca reactions

The results of the experiments aimed at the synthesis of Fl isotopes in the 239Pu + 48Ca and 240Pu + 48Ca reactions are presented. The experiment was performed using the Dubna gas-filled recoil separator at the U400 cyclotron. In the 239Pu+48Ca experiment one decay of spontaneously fissioning 284Fl was detected at 245-MeV beam energy. In the 240Pu+48Ca experiment three decay chains of 285Fl were detected at 245 MeV and four decays were assigned to 284Fl at the higher 48Ca beam energy of 250 MeV. The α-decay energy of 285Fl was measured for the first time and decay properties of its descendants 281Cn, 277Ds, 273Hs, 269Sg, and 265Rf were determined more precisely. The cross section of the 239Pu(48Ca,3n)284Fl reaction was observed to be about 20 times lower than those predicted by theoretical models and 50 times less than the value measured in the 244Pu+48Ca reaction. The cross sections of the 240Pu(48Ca,4-3n)284,285Fl at both 48Ca energies are similar and exceed that observed in the reaction with lighter isotope 239Pu by a factor of 10. The decay properties of the synthesized nuclei and their production cross sections indicate rapid decrease of stability of superheavy nuclei with departing from the neutron number N=184 predicted to be the next magic number.

Automation of experiments at Dubna Gas-Filled Recoil Separator

Approaches to solving the problems of automation of basic processes in long-term experiments in heavy ion beams of the Dubna Gas-Filled Recoil Separator (DGFRS) facility are considered. Approaches in the field of spectrometry, both of rare α decays of superheavy nuclei and those for constructing monitoring systems to provide accident-free experiment running with highly radioactive targets and recording basic parameters of experiment, are described. The specific features of Double Side Silicon Strip Detectors (DSSSDs) are considered, special attention is paid to the role of boundary effects of neighboring p–n transitions in the “active correlations” method. An example of an off–beam experiment attempting to observe Zeno effect is briefly considered. Basic examples for nuclear reactions of complete fusion at 48Ca ion beams of U-400 cyclotron (LNR, JINR) are given. A scenario of development of the “active correlations” method for the case of very high intensity beams of heavy ions at promising accelerators of LNR, JINR, is presented.

Production of intense metal ion beams from ECR ion sources using the MIVOC method

The production of metal ion beams by electron cyclotron resonance (ECR) ion sources using the MIVOC (Metal Ions from Volatile Compounds) method is described. The method is based on the use of metal compounds which have high vapor pressure at room temperature, e.g., C2B10H12, Fe(C5H5)2, etc. Intense ion beams of B and Fe were produced using this method at the FLNR JINR cyclotrons. Experiments on the production of cobalt, chromium, vanadium, germanium, and hafnium ion beams were performed at the test bench of ECR ion sources. Main efforts were put into production and acceleration of 50Ti ion beams at the U-400 cyclotron. The experiments on the production of 50Ti ion beams were performed at the test bench using natural and enriched compounds of titanium (CH3)5C5Ti(CH3)3. In these experiments, 80 μA 48Ti5+ and 70 μA 48Ti11+ beam currents were obtained at different settings of the source. Following successful tests, two 3-week runs were performed with 50Ti beams at the U-400 cyclotron aimed to perform experiments on the spectroscopy of superheavy elements. The intensity of the injected 50Ti5+ beam was 50–60 μA. The source worked stably during experiments. The compound consumption rate was determined at about 2.4 mg/h, which corresponded to the 50Ti consumption of 0.6 mg/h.

Experimental tests of the modernized VASSILISSA separator (SHELS) with the use of accelerated 50Ti ions

A high intensity ion beam of 50Ti ions was obtained using the ECR ion source on the U400 cyclotron. The experimental tests using accelerated 50Ti ions were performed with a modernized VASSILISSA separator (SHELS). Data has been obtained on the transmission coefficients of recoil nuclei synthesized in complete fusion reactions. Estimates from ion optical calculations performed in the design phase of the project of modernizing the separator are completely confirmed.

Preparation and high intensity heavy ion irradiation tests of intermetallic 243Am/Pd targets

Previously reported preparation method for Pd-based intermetallic targets (Usoltsev, et al., 2012) [1] has been successfully applied for producing two stationary 243Am/Pd targets. Both targets have been irradiated at the U-400 cyclotron at Flerov Laboratory of Nuclear Reactions Dubna (Russian Federation) using high intensity beams (up to 0.83μApart) of 48Ca18+. Alpha-particle spectroscopy and light microscopy allowed for a comprehensive characterization of the intermetallic targets before and after irradiation. A natNd/Pd intermetallic target and a solely electroplated 243Am/Ti target were similarly investigated for comparison.

Investigation of the243Am+48Careaction products previously observed in the experiments on elements 113, 115, and 117

Results from the production and decay properties of element 115 nuclei observed using the reaction ${}^{243}\mathrm{Am}+{}^{48}\mathrm{Ca}$ at various beam energies between November 1, 2010, and February 26, 2012, at the Dubna Gas Filled Recoil Separator are presented. This long-running experiment with a total beam dose of $3.3\ifmmode\times\else\texttimes\fi{}{10}^{19}$ and carried out in the excitation energy range ${E}^{*}=31$--47 MeV of the ${}^{291}$115 compound nucleus resulted in observation of three isotopes of element 115 with masses 287, 288, and 289. The 28 detected decay chains of ${}^{288}$115 show that this isotope is produced with the maximum probability at ${E}^{*}=34.0$--38.3 MeV with a corresponding cross section of ${\ensuremath{\sigma}}_{3n}=8.{5}_{\ensuremath{-}3.7}^{+6.4}$ pb. The four events attributed to the isotope ${}^{289}$115 that decays via a short $\ensuremath{\alpha}\ensuremath{\rightarrow}\ensuremath{\alpha}\ensuremath{\rightarrow}\text{SF}$ chain could be detected only at the lowest excitation energy ${E}^{*}=31$--36 MeV, in accordance with what could be expected for the 2$n$-evaporation channel of the reaction. The decay characteristics of this nuclide were established earlier (2010) and more recently (2012) in the reaction ${}^{249}$Bk(${}^{48}$Ca,4$n$)${}^{293}$117 and following $\ensuremath{\alpha}$ decay to ${}^{289}$115. At the energy ${E}^{*}=44.8\ifmmode\pm\else\textpm\fi{}2.3$ MeV we observed only a single long chain of the isotope ${}^{287}$115. The decay properties of nuclei starting at ${}^{288}$115 and ${}^{287}$115 isotopes obtained in the present work reproduce in full the results of the first experiment of 2003 that reported the discovery of elements 115 and 113. The excitation functions of the production of the isotopes of element 115 and observation of the isotope ${}^{289}$115 in cross-bombardment reactions with the targets of ${}^{243}$Am and ${}^{249}$Bk provide additional evidence of the identification of the nuclei of elements 115 and 113. The experiments were carried out using the ${}^{48}$Ca beam of the U400 cyclotron of the Flerov Laboratory of Nuclear Reactions, JINR.

Parameter monitoring and control system of Dubna Gas-Filled Recoil Separator

A modified integrated parameter-monitoring and control system for experiments on the synthesis of superheavy nuclei at the U-400 cyclotron of the Flerov Laboratory of Nuclear Reactions is considered. Experiments on the irradiation of heavy actinide targets were performed at the Dubna Gas-Filled Recoil Separator (DGFRS) [1]. This system consists of three components, namely, the detection module parameter control subsystem, the beam parameter monitoring subsystem, and the separator technical parameter control subsystem. The system is designed in CAMAC standard, the software is written under Windows XP using RAD Borland C++ Builder 6.0 and Kk009Pci interface (LNR) [2, 3].

Obtaining monochromatic beams of radioactive nuclei with energies near the Coulomb barrier on joint institute of nuclear research accelerator complex DRIBs

Two methods for obtaining monochromatic beams of radioactive nuclei with energies near the Coulomb barrier on Joint Institute of Nuclear Research accelerator complex DRIBs are described. In the first method, an MSP-144 magnetic spectrometer was used as the monochromator of low-energy 6He beam obtained after passing through an energy degrader. In the second method, a specially developed probe was used for experiments with the internal beam of the DRIBs complex post-accelerator (the U-400 cyclotron).

Influence of temperature during irradiation on the structure of latent track in polycarbonate

Stacks consisting of several layers of polycarbonate foils 10 μm thick were irradiated with U, Sm and Ni ions at the UNILAC (GSI, Darmstadt) and with Kr ions from the U-400 cyclotron (JINR, Dubna). The energy of the ions varied from 1 to 11 MeV/u. The irradiation with each ion species was performed at room temperature (RT) and at low temperatures (80 K or 15 K). The irradiated samples were etched with aqueous NaOH solutions in a conductometric cell. The effective pore diameter as a function of the etching time was calculated assuming cylindrical geometry of the etched out channels. The conductometric curve consisted of three parts which we identified as the track core, track halo and bulk etching. Radii of both track core and halo increased with increasing ion mass, and were consistent with the power-law energy-loss dependence. The size of the track core was found to not depend on the temperature during irradiation. Since this result was obtained in experiments performed at two different accelerator facilities and with four different projectiles of various energies, it can be considered as the one of high confidence level. In contrast, the radius of the halo tended to decrease with decreasing irradiation temperatures. However, reproducibility of the track halo radius estimates was quite poor which might be caused by some uncontrolled experimental factors influencing post-irradiation chemical reactions.

Obtaining monochromatic beams of accelerated 6He ions with a near-Coulomb-barrier energy on the DRIB accelerator complex at the JINR

Two methods for obtaining monochromatic beams of accelerated 6He ions with energies around the Coulomb barrier on the DRIB accelerator complex at the Joint Institute for Nuclear Research (JINR) is described. In the first method, the MSP-144 magnetic spectrometer is used as a monochromator of low-energy 6He beam after its passing through an energy absorber. The energy resolution of the 6He beam, which is 500 keV, is governed by the linear dimension of the target in the focal plane (18 mm). In the other method, a special probe is used to investigate nuclear reactions with accelerated 6He beams without loss of the beam intensity. With this probe, it is possible to perform experiments on the internal beam of the postaccelerator (U-400 cyclotron) of the DRIB complex. As a result, a 6He beam with a required energy and a beam resolution of 150 keV or better is produced at the target.

Ohmic heated sheet for the Ca ion beam production

The production of intense accelerated (48)Ca ion beams is the key problem in the experiments on the synthesis of new superheavy nuclei. For this purpose in the FLNR (JINR), an electron cyclotron resonance ion source is used at the U-400 cyclotron. The combination of a micro oven with a hot tantalum sheet inside the discharge chamber allowed the production of the intense (48)Ca(5+) ion beam at the (48)Ca consumption of about 0.5 mg/h. In this case, the tantalum sheet is heated by microwaves and plasma electrons. The microwave power of up to 500 W is required to heat the sheet to the temperature of about 500 degrees C. To decrease the required microwave power, a new sheet with a direct Ohmic heating was designed. The present paper describes the method, technique, and preliminary experimental results on the production of the Ca ion beam.

GABRIELA setup for nuclear spectroscopy of the transfermium element isotopes at the VASSILISSA separator

The JINR (Dubna)-IN2P3 (France) Collaboration project aimed at the α, β γ, spectroscopy of the transfermium element isotopes using heavy-ion beams of the U-400 cyclotron and the modernized recoil separator VASSILISSA was launched at Dubna. During the first full-scale experiment in September–October 2004, nobelium and lawrencium isotopes produced in the 48Ca + 207,208Pb → 255,256No* and 48Ca + 209Bi → 257Lr* reactions were studied.