The reactions 238U(54Cr,4n)288Lv and 242Pu(50Ti,3-4n)288,289Lv were studied at the Dubna Gas-filled Recoil Separator (DGFRS-2). Three new isotopes were discovered: the α-decaying 288Lv and 289Lv, as well as the spontaneously fissioning 280Cn (observed after the α decay of 284Fl). The cross section of the 4n channel for the reaction 238U + 54Cr turned out to be approximately 15-fold lower than the total cross section of the reaction 242Pu + 50Ti at an excitation energy of 292Lv of 41 MeV. This indicates that the cross sections of reactions with actinides using 50Ti are roughly an order of magnitude greater than those with 54Cr for the synthesis of 119 and 120 elements.

Background: Charge equilibration is a crucial phenomenon of nuclear dynamics observed in collisions of heavy nuclei characterized by varying neutron-to-proton (N/Z) ratios. This process involves equalizing the N/Z ratios of fragments, which occurs at the initial stage of nuclear reaction. Purpose: This work focuses on a theoretical investigation of the charge equilibration process that occurs during low-energy collisions of heavy nuclei, and on examining its impact on multinucleon transfer and fusion processes. Method: A multidimensional dynamical model of nucleus-nucleus collisions based on the Langevin equations [A. V. Karpov et al., Phys. Rev. C 96, 024618 (2017)] was employed in this work. Results: A broad set of experimental data on multinucleon transfer products of the 40Ca, 56Fe, 58Ni, 64Ni + 208Pb reactions was analyzed within the dynamical model. The agreement of the calculated energy, atomic number, angular, and isotopic distributions of the reaction products with corresponding experimental data enabled us to refine the model parameters governing the time of nuclear neck evolution and the nucleon transfer rate. Based on this analysis, the mechanism and duration of 0.5 zs for the charge equilibration process were determined. An influence of N/Z equilibration was observed on capture and fusion processes in the 40Ca, 48Ca+ 208Pb reactions. Conclusions: Equilibration of N/Z ratios of fragments is primarily driven by the minimization of the potential energy of the system. This process predominantly occurs along an optimal path, and involves the redistribution of neutrons and protons between the fragments in opposite directions. The products formed in these multinucleon transfer channels exhibit increased cross sections. The decrease in the potential energy of the system during the charge equilibration leads to an enhancement of multinucleon transfer and fusion processes, which are particularly evident at energies below the potential barrier.

The 238U(54Cr, 4n) 288Lv and 242Pu(50Ti, 3n-4n) 288,289Lv reactions have been studied at the gas-filled separator DGFRS-2 at the SHE Factory at Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. Three new isotopes were discovered: two alpha-decaying nuclei 288Lv with alpha-particle energy E alpha = 11.08 MeV and half-life T1/2 = 2.0 ms, 289Lv with E alpha = 10.90 MeV, T1/2 = 2.4 ms, and granddaughter of 288Lv, spontaneously fissioning 280Cn with T1/2 = 10 mu s, which was observed after the first registration of alpha decay of 284Fl with E alpha = 10.57 MeV. Besides, for the first time we reliably registered the pxn channel of the 242Pu + 50Ti reaction which was not evidently observed in the 48Ca-induced reactions in previous studies. The cross sections of the 3n and 4n channels of the 242Pu + 50Ti reaction of 0.32+0.34 -0.18 pb and 0.22+0.27 -0.15 pb, respectively, were measured at excitation energy of the 292Lv compound nucleus E & lowast; = 41 MeV. The cross section of the 4n-evaporation channel of the 238U + 54Cr reaction, leading to the same compound nucleus, at E & lowast; = 42 MeV of 32+46 -24 fb turned out to be approximately 15 times lower than the total cross section of the 242Pu + 50Ti reaction at close excitation energy. Thus, for the first time, it was convincingly proved in an experiment that the reactions of isotopes of actinide elements with 50Ti are, by an order of magnitude, preferable to reactions with 54Cr for the synthesis of new elements 119 and 120.

We present studies of multinucleon transfer reactions in collisions of Ca-48 +Pb-208, Ti-50 +Pb-208, and Ar-40 +Bi-209 which lead to the population of nuclei with proton numbers greater than the target proton number. The target- like reaction products were separated in flight using the velocity filter SHELS of the Flerov Laboratory for Nuclear Reactions (FLNR), Dubna. Our goal was to examine transfer reactions for producing new heavy and superheavy nuclei and to assess the applicability of velocity filters for their investigation. We observed and studied about 40 different nuclides, resulting from the transfer of up to eight protons from the projectile to the target and moving in forward direction relative to the beam axis. We present cross-section systematics for isotopes of elements Z = (83 - 91) measured in our experiment and compare them with available data from transfer reactions with actinide targets which lead to isotopes up to Z = 103.

Background: Multinucleon transfer (MNT) reactions are considered now as a possible tool to produce new isotopes of heavy and superheavy elements. Purpose: Experimental study of MNT fragments formed in the 136Xe + 238U reaction at 136Xe beam energy of 1.11 GeV and comparison with theoretical calculations. Methods: Primary and secondary mass and energy distributions of projectilelike fragments (PLF) formed in the 136Xe + 238U reaction have been experimentally investigated independently and in coincidence with survived heavy targetlike fragments (TLF) using the CORSET setup. Since the heavy fragments formed in the reactions are highly excited the masses, energies, and angles of both fragments as products of the sequential fission of heavy MNT fragments have been measured. Results: The cross sections for PLFs at 27.2 degrees Blab 32.8 degrees along with survived TLFs and TLFs undergoing fission have been obtained. The mass loss during the deexcitation process of excited PLFs has been found using the measured primary and secondary masses. The excitation energies of light and heavy MNT fragments have been estimated from the mass loss and total kinetic energies. An overall good agreement with theoretical calculations increases reliability of performed analysis. Conclusions: The transfer of about 27 nucleons from the projectile to target nucleus has been found. The cross section of the heaviest observed fragment with the mass of 265 u is about few hundred microbarns. The survival probabilities of transtarget nuclei formed in the reaction drop rapidly from approximate to 7 x 10-1 for the fragment mass of 240 u to approximate to 1.8 x 10-3 for 255 u.

Background: Multinucleon transfer (MNT) reactions are considered now as a possible tool to produce new isotopes of heavy and superheavy elements.Purpose: Experimental study of MNT fragments formed in the $^{136}\mathrm{Xe}+^{238}\mathrm{U}$ reaction at $^{136}\mathrm{Xe}$ beam energy of 1.11 GeV and comparison with theoretical calculations.Methods: Primary and secondary mass and energy distributions of projectilelike fragments (PLF) formed in the $^{136}\mathrm{Xe}+^{238}\mathrm{U}$ reaction have been experimentally investigated independently and in coincidence with survived heavy targetlike fragments (TLF) using the CORSET setup. Since the heavy fragments formed in the reactions are highly excited the masses, energies, and angles of both fragments as products of the sequential fission of heavy MNT fragments have been measured.Results: The cross sections for PLFs at $27.{2}^{\ensuremath{\circ}}\ensuremath{\le}{\ensuremath{\theta}}_{\mathrm{lab}}\ensuremath{\le}32.{8}^{\ensuremath{\circ}}$ along with survived TLFs and TLFs undergoing fission have been obtained. The mass loss during the deexcitation process of excited PLFs has been found using the measured primary and secondary masses. The excitation energies of light and heavy MNT fragments have been estimated from the mass loss and total kinetic energies. An overall good agreement with theoretical calculations increases reliability of performed analysis.Conclusions: The transfer of about 27 nucleons from the projectile to target nucleus has been found. The cross section of the heaviest observed fragment with the mass of 265 u is about few hundred microbarns. The survival probabilities of transtarget nuclei formed in the reaction drop rapidly from $\ensuremath{\approx}7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}$ for the fragment mass of 240 u to $\ensuremath{\approx}1.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ for 255 u.

An exploratory program to establish the multi-nucleon transfer (MNT) reaction as a new research direction at the FRS Ion Catcher (FRS-IC) has started at GSI. Its long term goal is the use of secondary exotic beams from the Super-FRS to drive MNT reactions. The near term goal is to perform proof-of-principle cross section and mass measurements with slowed-down 238U beams on targets inside the FRS-IC gas cell. The experimental efficiencies and expected rates are estimated using production cross sections from the Langevin MNT model followed by simulations of the full setup. The impact of the space charge effect inside the gas cell is evaluated in detail.

The dependence of the properties of the fission fragments formed both in the fusion-fission and fast fission processes on the angular momentum still remains very unclear from an experimental as well as theoretical point of view. To study the properties of fast fission fragments of preactinide nuclei as function of the interaction energy and introduced angular momentum, the mass-energy distributions of ^184 Pb fission fragments formed in the ^40Ca+^144 Sm reaction at energies above the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the ^40 Ca ions’ energies of 212, 231, 244, and 277 MeV. The mass-energy distributions of the fast fission fragments have been extracted by subtracting the mass-energy matrices corresponding to the compound nucleus fission from those of all measured fissionlike events. The asymmetric fragments with masses 76 and 108 u were found to be the most probable in the fast fission of ^184 Pb. With increasing ^40 Ca energy from 231 to 277 MeV the mass distributions of fast fission fragments change weakly, whereas an increase in the TKE is about 20 MeV. The properties found for the fast fission fragments indicate the incomplete mass relaxation and not full energy dissipation.

Background: The stability of the transfermium nucleus against fission is mainly determined by the shell correction depending on its angular momentum and excitation energy.Purpose: The study of the fast fission process of the transfermium nucleus $^{248}\mathrm{No}$ and its dependence on the interaction energy and introduced angular momentum.Methods: Mass-energy distributions of the $^{248}\mathrm{No}$ fission fragments formed in the $^{40}\mathrm{Ca}$ + $^{208}\mathrm{Pb}$ reaction at energies above the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the $^{40}\mathrm{Ca}$-beam energies of 223, 250, and 284 MeV.Results: The contribution of the fast fission process is determined from the calculations of the driving potential, taking into account shell effects and rotational energy and amounts to 39% and 61% at 250 and 284 MeV, respectively. The mass-energy distributions of the quasifission and fast fission fragments have been extracted by subtracting the mass-energy matrices associated with compound nucleus fission from those of all measured fissionlike events. The asymmetric fragments with masses 97 and 151 u were found to be the most probable in the fast fission of $^{248}\mathrm{No}$. With increasing $^{40}\mathrm{Ca}$ energy from 250 to 284 MeV the mass distributions of the fast fission fragments change slightly.Conclusions: Contrary to quasifission in which the fragments are focused mainly around the closed neutron or proton shells, the influence of known proton or neutron shells on the asymmetric mass distribution in the fast fission process was not observed.

Background: The stability of the transfermium nucleus against fission is mainly determined by the shell correction depending on its angular momentum and excitation energy. Purpose: The study of the fast fission process of the transfermium nucleus No-248 and its dependence on the interaction energy and introduced angular momentum. Methods: Mass-energy distributions of the No-248 fission fragments formed in the Ca-40 + Pb-208 reaction at energies above the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the Ca-40-beam energies of 223, 250, and 284 MeV. Results: The contribution of the fast fission process is determined from the calculations of the driving potential, taking into account shell effects and rotational energy and amounts to 39% and 61% at 250 and 284 MeV, respectively. The mass-energy distributions of the quasifission and fast fission fragments have been extracted by subtracting the mass-energy matrices associated with compound nucleus fission from those of all measured fissionlike events. The asymmetric fragments with masses 97 and 151 u were found to be the most probable in the fast fission of No-248. With increasing Ca-40 energy from 250 to 284 MeV the mass distributions of the fast fission fragments change slightly. Conclusions: Contrary to quasifission in which the fragments are focused mainly around the closed neutron or proton shells, the influence of known proton or neutron shells on the asymmetric mass distribution in the fast fission process was not observed.

The production of very neutron-rich nuclides heavier than fission fragments is an ongoing experimental challenge. Multi-nucleon transfer reactions (MNT) have been suggested as a method to produce these nuclides. By thermalizing the reaction products in gas-filled stopping cells, we can deliver them as cooled high-quality beams to decay, laser and mass spectrometry experiments. High precision mass spectrometry will allow for the first time to universally and unambiguously identify the atomic and proton numbers of the ions produced in MNT reactions. In this way their ground and isomeric state properties can be studied in high-precision measurements. In experiments at IGISOL, Finland and at FRS Ion Catcher, Germany, we have done and will perform broadband measurements of the reaction products, with the aim to improve the understanding of the reaction mechanism and to determine the properties of the ground and isomeric states of the produced nuclides. First results and preparations for upcoming experiments are presented.

t—The mass–energy distributions of fission fragments of excited 180,190Hg nuclei formed in 36Ar + 144,154Sm reactions are measured at incident 36Ar energies of 158, 181, and 222 MeV using the double-arm time-of-flight spectrometer CORSET. The asymmetric fission of 180,190Hg with the most probable masses of light and heavy fragments of 79 and 101 amu, and 84 and 106 amu, respectively, is observed in mass distributions of 180,190Hg at energies of excitation of up to 75 MeV. Two components manifesting the symmetric and asymmetric fission modes are observed in the kinetic energy distributions.

Charge equilibration is analyzed in the context of the dynamic approach based on the Langevin equations. The time and energy dependences of this process are discussed. Analysis of the isotopic distributions of the final products obtained in the 40Ca, 58Ni and 64Ni + 208Pb shows that charge equilibration process strongly affects the multinucleon transfer in them. Yields of the most neutron-rich heavy nuclides obtained in the 58Ni and 64Ni + 208Pb reactions are discussed.