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The mass-energy distributions of fragments originating from the fission of the compound nucleus 226Th and their correlations with the multiplicity of gamma rays emitted from these fragments are measured and analyzed in 18O + 208Pb interaction induced by projectile oxygen ions of energy in the range E lab = 78–198.5 MeV. Manifestations of an asymmetric fission mode, which is damped exponentially with increasing E lab, are demonstrated. Theoretical calculations of fission valleys reveal that only two independent valleys, symmetric and asymmetric, exist in the vicinity of the scission point. The dependence of the multiplicity of gamma rays emitted from both fission fragments on their mass, Mγ(M), has a complicated structure and is highly sensitive to shell effects in both primary and final fragments. A two-component analysis of the dependence Mγ(M) shows that the asymmetric mode survives in fission only at low partial-wave orbital angular momenta of compound nuclei. It is found that, for all E lab, the gamma-ray multiplicity Mγ as a function of the total kinetic energy (TKE) of fragments, Mγ(TKE), decreases linearly with increasing TKE. An analysis of the energy balance in the fission process at the laboratory energy of E lab = 78 MeV revealed the region of cold fission of fragments whose total kinetic energy is TKE ∼Q max.

Mass-energy distributions (MEDs) and capture-fission cross sections have been measured in the reaction 48 Ca + 208 Pb → 256 No at the energies E lab = 206 – 242 MeV using a double-arm time-of-flight spectrometer CORSET. It has been observed that MED of the fragments consists of two parts, namely, the classical fusion–fission process corresponding to the symmetric fission of 256 No and quasi-fission “shoulders” corresponding to the light fragment masses ∼ 60 – 90 u and complimentary heavy fragment masses. The quasi-fission “shoulders” have a higher total kinetic energy (TKE) as compared with that expected for the classical fission. A mathematical formalism was employed for the MEDs fragment decomposition into fusion–fission and quasi-fission components. In the fusion–fission process a high-energy Super-Short mode has been discovered for the masses M H = 130 – 135 u and the TKE of ≈ 233 MeV .

The CORSET time-of-flight spectrometer has been developed at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research (Dubna, Russia) for investigating binary products of nuclear reactions. The spectrometer has been used to study the dynamics of fusion-fission and quasi-fission of superheavy elements. The design and the main characteristics of the spectrometer, as well as the algorithms for deducing the mass-energy distributions of fragments and the cross sections of nuclear reactions, are presented. The spectrometer contains two time-of-flight arms based on microchannel-plate detectors and three telescopes, each of which is composed of two microchannel-plate detectors and one semiconductor detector. A system of four semiconductor detectors is used to obtain the absolute value of a cross section. The time resolution of the time-of-flight arms is 150 ps, which allows the time-of-flight distances to be set at 10–20 cm, thus providing a mass resolution of 3 amu and an angular resolution of 0.3°. Owing to these characteristics, the spectrometer can be used as a trigger in multidetector setups for measuring light charged particles, neutrons, and γ rays in coincidence with reaction fragments.

The average multiplicity of gamma rays emitted by fragments originating from the fission of 226Th nuclei formed via a complete fusion of 18O and 208Pb nuclei at laboratory energies of 18O projectile ions in the range E lab = 78–198.5 MeV is measured and analyzed. The total spins of fission fragments are found and used in an empirical analysis of the energy dependence of the anisotropy of these fragments under the assumption that their angular distributions are formed in the vicinity of the scission point. The average temperature of compound nuclei at the scission point and their average angular momenta in the entrance channel are found for this analysis. Also, the moments of inertia are calculated for this purpose for the chain of fissile thorium nuclei at the scission point. All of these parameters are determined at the scission point by means of three-dimensional dynamical calculations based on Langevin equations. A strong alignment of fragment spins is assumed in analyzing the anisotropy in question. In that case, the energy dependence of the anisotropy of fission fragments is faithfully reproduced at energies in excess of the Coulomb barrier (E c.m. − E B ≥ 30 MeV). It is assumed that, as the excitation energy and the angular momentum of a fissile nucleus are increased, the region where the angular distributions of fragments are formed is gradually shifted from the region of nuclear deformations in the vicinity of the saddle point to the region of nuclear deformations in the vicinity of the scission point, the total angular momentum of the nucleus undergoing fission being split into the orbital component, which is responsible for the anisotropy of fragments, and the spin component. This conclusion can be qualitatively explained on the basis of linear-response theory.

Correlations between folding angular distributions of fission fragments and the gamma-ray multiplicity are studied for 18O + 208Pb interactions at energies of the beam of 18O ions in the range E lab = 78–198.5 MeV. The probabilities are determined for complete-and incomplete-fusion processes inevitably followed by the fission of nuclei formed in these processes. It is found that the probability of incomplete fusion followed by fission increases with increasing energy of bombarding ions. It is shown that, for the incomplete-fusion process, folding angular distributions of fission fragments have a two-component structure. The width of folding angular distributions (FWHM) for complete fusion grows linearly with increasing energy of 18O ions. The multiplicity of gamma rays from fission fragments as a function of the linear-momentum transfer behaves differently for different energies of projectile ions. This circumstance is explained here by the distinction between the average angular momenta of participant nuclei in the fusion and fission channels, which is due to the difference in the probabilities of fission in the cases where different numbers of nucleons are captured by the target nucleus.

An overview of results in fusion studies with stable beams spanning different mass regions and energy ranges is presented. The advantages offered by studying channel coupling effects, involving low-lying excited states of the colliding nuclei, as well as the difficulties in understanding the influence of transfer couplings on fusion, are firstly remarked. The competition of fusion with quasi-fission in heavy systems and the unexpected steep falloff of fusion cross sections at far sub-barrier energies are finally discussed.

Fission fragment mass and energy distributions (MED) and fission fragment folding angle distributions (FFFAD) have been measured in the reaction 6Li + 232Th within the lithium projectile energy range E lab = 28.5 – 62.5 MeV . The values of the ratio between the complete and incomplete fusion cross-sections have been obtained from a combined analysis of MED and FFFAD. The incomplete fusion originates from transfer reactions and/or from the 6Li breakup mainly into α and d clusters. It has been found that the contribution of complete fusion into the total fusion–fission cross-section is only ∼ 27 % at the lithium projectile energy E lab = 28.5 MeV ( ∼ 2 MeV below the Coulomb barrier).

The competition between fusion-fission and quasi-fission in the reactions 48 Ca+ 208 Pb and 48 Ca+ 244 Pu(E * = 40MeV) is investigated using the pre-scission neutron multiciplicity distributions ( PSNMD ) obtained with a new analysis protocol.

Average prescission Mpren and postscission Mpostn neutron multiplicities as well as average γ-ray multiplicity 〈Mγ〉, average energy 〈Eγ〉 emitted by γ-rays as a function of mass and total kinetic energy (TKE) of fission fragments were measured in proton induced reactions p+ 242 Pu→ 243 Am , p+ 238 U→ 239 Np at proton energy Ep=13, 20 and 55 MeV.

Fusion-fission and fusion-evaporation cross sections have been measured in a large energy range for the 4 8 Ca+ 1 6 8 Er, 1 5 4 Sm reactions. The comparison of the reduced evaporation data for such reactions and for collisions induced by light projectiles leading to the same compound nuclei 2 1 6 Ra* and 2 0 2 Pb* puts in evidence a fusion hindrance, which is particularly large for the first composite system. This fusion suppression is consistent with a noticeable contribution coming from quasi-fission events observed in the mass-energy distribution of fission fragments. The asymmetric shape of the quasi-fission component has been explained in terms of shell effects in the exit channel, favouring the population of closed shell fission fragments. The comparison of 4 8 Ca+ 1 5 4 Sm with preliminary data on 4 8 Ca+ 1 4 4 Sm seems to suggest that the target deformation plays a role in the onset of the quasi-fission mechanism.

We have studied mass-energy distributions (MED) of fission fragments using two projectile-target combinations, 12C + 204Pb and 48Ca + 168Er, leading to the same compound nucleus 216Ra at the excitation energy E*∼40 MeV. It has been found that the contribution of the asymmetric mode in the case of the former reaction is 1.5%, and it is 30% in the case of the latter one. We connect such a sharp increase in the yield of asymmetric products in the 48Ca + 168Er reaction with the quasifission process, the MED of which have a clearly expressed shell structure. The characteristics of the fission fragment MED are of such a kind that they can be interpreted by analogy with the low-energy fission of heavy nuclei as a manifestation of an independent mode of nuclear decay which competes with the classical fusion-fission process.

The talk presents the results of an investigation of the main characteristics (mass and energy distributions of fission fragments and multiplicity of neutrons) of the fission of the nuclei of 220 Ra, 226 Th, 256 No, 270 Sg, 286 112 produced in reactions with ions of 18 O, 22 Ne and 48 Ca at energies close to and essentially below the Coulomb barrier. The data obtained show that the form of the mass and energy distributions of the fission fragments of 226 Th and 270 Sg is accounted for by the multimodal nature of the fission. In addition, for 226 Th, a new phenomenon was established there is a significant difference between the numbers of prescission neutrons for symmetric and asymmetric fission modes. It was found that, for the low-energy fission of the nucleus of 286 112, the mass distribution of the fragments is of a clear-cut asymmetric form, contrary to what is observed for the spotaneous fission of the nuclei with Z = 100–104 and for the induced fission of 270 Sg.

Multinucleon transfer reactions in 40Ca+96Zr and 90Zr+208Pb have been measured at energies close to the Coulomb barrier in a high resolution gamma-particle coincidence experiment. The large solid angle magnetic spectrometer PRISMA coupled to the CLARA gamma-array has been employed. Trajectory reconstruction has been applied for the complete identification of transfer products. Mass and charge yields, total kinetic energy losses, gamma transitions of the binary reaction partners, and comparison of data with semiclassical calculations are reported. Specific transitions in 95Zr populated in one particle transfer channels are discussed in terms of particle-phonon couplings. The gamma decays from states in 42Ca in the excitation energy region expected from pairing vibrations are also observed., Comment: 10 pages, 9 figures

International audience; Average preequilibrium $\langle M_n^{preeq}\rangle$ average statistical prescission $\langle M_n^{stpre}\rangle$ and postscission $\langle M_n^{post}\rangle$ neutron multiplicities as well as average gamma-ray multiplicity $\langle M_{gamma}\rangle$, average energy emitted by gamma-rays $\langle E_{gamma}\rangle$ and average energy per one gamma quantum $\langle\varepsilon_{gamma}\rangle$ as a function of mass and total kinetic energy (TKE) of fission fragments were measured in the proton-induced reactions p+^{232}Th \to ^{233}Pa, p+^{238}U \to ^{239}Np and p+^{242}Pu \to ^{243}Am (at proton energy E_p=13, 20, 40 and 55 MeV). The fragment mass and energy distributions (MEDs) have been analyzed in terms of the multimodal fission. The decomposition of the experimental MEDs onto the MEDs of the distinct modes has been fulfilled in the framework of a method that is free from any parameterization of the distinct fission mode mass distribution shapes. The main characteristics for symmetric and asymmetric modes have been studied in their dependence on the compound nucleus composition and proton energy. The manifestation of multimodal fission in average gamma-ray multiplicities $\langle E_{gamma}\rangle$ of fission fragments was also studied in this work.

The CLARA-PRISMA setup is a powerful tool for spectroscopic studies of neutron-rich nuclei produced in multi-nucleon transfer and deep-inelastic reactions. It combines the large acceptance spectrometer PRISMA with the gamma-ray array CLARA. At present, the ancillary heavy-ion detector DANTE, based on Micro-Channel Plates to be installed at the CLARA-PRISMA setup, is being constructed at LNL. DANTE will open the possibility of measuring gamma-gamma-Doppler-corrected coincidences for the events outside the acceptance of PRISMA. In this presentation, it is described the heavy-ion detector DANTE, as well as the performances of the first prototype.

The interest in the study of the fission process of superheavy nuclei mainly deals with the opportunity to obtain information about the cross-section of the compound nucleus (CN) formation at excitation energies E*\approx 15–30 MeV. It allows one to estimate the survival probability of the superheavy composite system after evaporation of 1–3 neutrons, i.e. in "cold" or "warm" fusion reactions. However, in order to solve this problem deeper understanding of the coalescence processes between colliding nuclei, the competition between fusion-fission and quasi-fission processes is needed. The characteristics of both processes, their manifestation in the experimental observables and the relative contribution to the capture cross-section in dependence on the excitation energies, reaction entrance channel etc were investigated for a wide range of target-projectile combinations. Results of the experiments devoted to the study of the fusion-fission and quasi-fission processes in the reactions of the formation of the superheavy nuclei with Z = 102–122 are presented. The heavy ions 26Mg, 48Ca, 50Ti, 58Fe and 64Ni were used as projectiles. The choice of the reactions with 48Ca and actinide-targets was inspired by the experiments on the production of the isotopes 283112, 289114 and 283116 in Dubna using the same reactions. The 50Ti, 58Fe and 64Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia) and the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) using the time-of-flight spectrometer of fission fragments CORSET. The role of the shell effects, the influence of the entrance channel asymmetry and the deformations of colliding nuclei on the mechanism of the fusion-fission and the competitive process of quasi-fission are discussed. The recent results on synthesis of superheavy nuclei and the perspectives of the "hot" fusion reaction for the production of superheavy nuclei are considered.

The mass-energy distributions of the fragments, fusion-fission (OFF) and capture (oCap) cross-sections in the reactions 26Mg+248Cm; 48Ca+2"RPb, 232Th, 238U , 2 4 4 ~ u , 2 4 8 ~ m ; 244Pu, 248Cm were measured at the U400 accelerator of Flerov Laboratory of Nuclear Reactions (JINR, Russia) with use of double-ann time-of-flight spectrometer CORSET. The influence of reaction entrance channel on the competition between fusion-fission and quasi-fission processes was studied. Strong manifestation of the shell effects in mass distributions of fusion-fission and quasi-fission fragments was observed. The multimodal fission phenomena were found for 2 7 4 H ~ and 256N0 nuclei at low excitation energies. % ~ ~ 2 0 8 p b , 232~h

Results of the experiments aimed at the study of fission and quasi‐fission processes in the reactions 12C+204Pb, 48Ca+144,154Sm, 168Er, 208Pb, 238U, 244Pu, 248Cm; 58Fe+208Pb, 244Pu, 248Cm, and 64Ni+186W, 242Pu are presented. The choice of the above‐mentioned reactions was inspired by the experiments on the production of the isotopes 283112, 289114 and 283116 at Dubna using the same reactions. The 58Fe and 64Ni projectiles were chosen since the corresponding projectile‐target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U‐400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia), the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) and the Accelerator of the Laboratory of University of Jyvaskyla (JYFL, Finland) using the time‐of‐flight spectrometer of fission fragments CORSET and the neutron multi‐detector DEMON. The role of shell effects and the influence of the entrance channel asymmetry and the deformatio...

Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions ^12C+^204Pb, ^48Ca-^144Sm, ^154Sm, ^168Er, ^208Pb, ^238U, ^244Pu, ^248Cm ; ^58Fe+^208Pb, ^244Pu, ^248Cm, and ^64Ni+^186W, ^242Pu are presented in the work. The choice of the above mentioned reactions was inspired by recent experiments on the production of the isotopes (283)112, (289)114 and (283)116 at Dubna [1], [2] using the same reactions. The Fe-58 and ^64Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the ^400U accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia), the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) and the Accelerator of the Laboratory of University of Jyvaskyla (JYFL, Finland) using the time-of-flight spectrometer of fission fragments CORSET[3] and the neutron multi-detector DEMON[4], [5]. The role of shell effects and the influence of the entrance channel on the mechanism of the compound nucleus fusion-fission and the competitive process of quasi-fission are discussed.

The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z = 82-122 formed in the reactions with ^48Ca and ^58Fe ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the ^400U accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro, (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multi-detector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments, fission, quasi-fission and evaporation residues cross sections, multiplicities of neutrons and gamma quanta and their dependence on the mechanism of formation and decay of compound systems have been studied.

Flerov Laboratory of Nuclear Reactions, JINR, 141 980 Dubna, Russia 'Universite Libre de Bruxelles, Bruxelles, Belgique 'Institut de Recherches Subatomiques, CNRS-IN2P3, Strasbourg, France 'Deparment of Physics, University of Jwiiskyla, FIN-40351, Jyvaskyla, Finland V. G. Khlopin Radium Institute, St.-Petersburg 194021, Russia 'Texas A&M lJniversi& Cyclotron Institute, College Station, Texas, 77843-3366, USA

Flerov Laboratory of Nuclear Reactions, JINR, 141980 Dubna, Russia I Universite Libre de Bruxelles, Bruxelles, Belgique 21nstitut de Recherches Subatomiques, CNRS-IN2P3, Strasbourg, France 'Department of Physics, University of Messina and INFN, Italy "Institute of Nuclear Physics of the National Nuclear Center of Kazakhstan 480082 Almaty, Kazakhstan 'Institute of Physics SASc, 84228 Bratislava, Slovakia

Fusion-evaporation and fusion-fission cross sections have been measured in the reaction 48 Ca+ 154 Sm from well below to well above the Coulomb barrier. The comparison of fusion cross sections for this reaction with previous data corresponding to 16 O+ 186 W, leading to the same compound nucleus 202 Pb * , puts in evidence an interesting competition between sub-barrier enhancement, due to the strong couplings related to the 154 Sm deformation, and above barrier suppression for the 48 Ca induced reaction. The fusion hindrance mechanism has been attributed to the strong quasi-fission component observed in the mass-energy distributions of fission fragments.

We have studied the mass and energy distributions of fission fragments from the two reactions ${}^{12}\mathrm{C}{+}^{204}\mathrm{Pb}$ and ${}^{48}\mathrm{Ca}{+}^{168}\mathrm{Er}$ that lead to the same compound nucleus ${}^{216}{\mathrm{Ra}}^{*}.$ Despite the fact that the excitation energy was around 40 MeV in both cases, the contribution from asymmetric fission in the first reaction is only around 1.5% but is about 30% in the second. This marked increase in the yield of asymmetric products is connected to the quasifission process, in which important shell effects become evident. The mass-energy distributions are interpreted in terms of an independent decay mode competing with the normal fusion-fission process and possibly leading to a significant suppression of the fusion cross section itself.

The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z = 82-122 formed in the reactions with Ca-48 and Fe-58 ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multidetector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments ; fission, quasifission, and evaporation residue cross sections ; and multiplicities of neutrons and gamma-quanta and their dependences on the mechanism of formation and decay of compound systems have been studied.

Near-barrier excitation functions have been measured for evaporation-residue production and fission in the 12C + 204,206,208Pb and 48Ca + 168,170Er systems that lead to the compound nuclei 216,218,220Ra*. A Pronounced suppression of evaporation-residue production is observed for the more symmetric combinations, 48Ca + 168,170Er. We relate this to the significant quasifission components already observed for these systems.

The time scales for nuclear fission have been explored using both pre- and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV /sup 16/O+/sup 176/Yb and /sup 208/Pb and 104-MeV /sup 4/He+/sup 188/Os and /sup 209/Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF/sub 2/ array. The pre- and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, gamma , and fission time scales. The gamma values ranged from 7 to 20, while the fission times were (31-105)*10/sup -21/s.

Two components in the ${M}_{\ensuremath{\gamma}}(M)$ distribution were established in detailed measurements of mean $\ensuremath{\gamma}$-ray multiplicities from fission fragments of ${}^{226}\mathrm{Th}$. For the first time in the ${M}_{\ensuremath{\gamma}}(M)$ dependencies we were able to distinguish two components associated with primary and the final (after the neutron evaporation) fission fragments, and show that at the scission point ${M}_{\ensuremath{\gamma}}$ is extremely sensitive to symmetric and asymmetric modes of fission. Theoretical calculations of the pre-scission shapes of the fissioning nuclei confirm our conclusions.

Two components in the M(gamma)(M) distribution were established in detailed measurements of mean gamma-ray multiplicities from fission fragments of (226)Th. For the first time in the M(gamma)(M) dependencies we were able to distinguish two components associated with primary and the final (after the neutron evaporation) fission fragments, and show that at the scission point M(gamma) is extremely sensitive to symmetric and asymmetric modes of fission. Theoretical calculations of the pre-scission shapes of the fissioning nuclei confirm our conclusions.

Results of fission fragment mass-energy distributions of the compound ${}^{226}\mathrm{Th}$ nucleus formed in the sub-barrier fusion reaction ${}^{18}\mathrm{O}{+}^{208}\mathrm{Pb}$ at an energy of ${}^{18}\mathrm{O}$ ions ${E}_{\mathrm{lab}}=78$ MeV are reported. The reaction has been studied twice using two different accelerators, and both sets of experimental data agree quite well. Performed analysis of the experimental data with the use of a new multicomponent method has shown that alongside the well-known modes, i.e., the symmetric (S) and two asymmetric modes standard-one and standard-two, a high-energy mode standard-three has manifested itself. The last named mode appears due to the influence of the close-to-sphere neutron shell with $N\ensuremath{\approx}50$ in the light fission fragment group. Theoretical calculations of the prescission shapes of the fissioning nuclei ${}^{224,226}\mathrm{Th}$ confirm this conclusion.

Mass-energy distributions of the ${}^{220}\mathrm{Ra}$ fission fragments produced in the ${}^{12}\mathrm{C}{+}^{208}\mathrm{Pb}$ reaction at projectile energies higher and deep below the Coulomb barrier have been measured using a two-arm time-of-flight spectrometer CORSET. It has been shown that an asymmetric component appears at the sides of the prevailing symmetric fission with a cooling of the compound nucleus. The component consists of two standard modes with average masses of $\ensuremath{\simeq}132$ and $\ensuremath{\simeq}139.$ A three-component structure has also been observed in the total kinetic energy distributions in the range of asymmetric fission fragment masses.

The fusion-fission reactions {sup 22}Ne + {sup 248}Cm and {sup 22}Ne + {sup 249}Cf were investigated at projectile energies equal to 102 and 127 MeV. Mass-energy distributions and yields are shown. Two-dimensional plots of TKE vs fragment mass are also shown for {sup 48}Ca reactions at 230 MeV with {sup 208}Pb and {sup 238}U, leading to {sup 256}No and {sup 286}112.

The neutron spectra associated to the two fission modes of Th-226 have been measured in coincidence with the fragment yields of the O-18 + Pb-208 reaction at E-lab = 78 MeV. The pre- and post-fission multiplicities and temperatures have been extracted. Surprisingly, the prefission neutron multiplicities associated with the asymmetric mode are larger than those associated with the symmetric mode.

The talk presents new results obtained in the study of fission of superheavy nuclei 256No, 270Sg and 286112 formed in reactions with 22Ne and 48Ca ions at energies near or considerably lower than the Coulomb barrier. The experiments have been performed at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (FLNR) with the use of the time-of-flight spectrometer of fission fragments CORSET.

The γ-rays from the multimodal fission of the 226Th formed in 18O+208Pb was investigated at the near- and sub-barrier energies. The corresponding excitation energies at the saddle point, Esp*, ranged from 23 to 26 MeV. The average γ-ray multiplicities and relative γ-ray energies as a function of the mass of the fission fragments exhibits a complex structure and strong variations. Such strong variations have never been previously observed in heavy ion-induced fusion-fission reactions. Obtained results may be explained with the influence of shell effects on the properties of the fission fragments. Present work is the one in series of investigation of the multimodal fission phenomena in At-Th region.

The fission of the systems 220,224,226Th was investigated by measuring the mass-energy distributions of the fission fragments. The corresponding excitation energies at the saddle point, Esp*, ranged from 16 to 40 MeV. As Esp* decreases, an asymmetric mass component becomes visible on the predominately symmetric mass distribution. The contribution of the asymmetric mode is characterized by the total yield ratio Ys/Ya, which decreases rapidly for the heavier isotopes of thorium. This behavior of Ys/Ya is in qualitative agreement with theoretical calculations. For all isotopes studied, the subtracted asymmetric fission component, Ya=Y1−Ys, exhibits a complex structure, actually showing two components, Ya=Ya1+Ya0, which have average masses Ma1=132 and Ma0=140.

Available data on evaporation residue (ER) production and fission in a wide region of compound nucleus (CN) masses and entrance-channel mass-asymmetry values have been analyzed in search for the 'starting point', where the fusion suppression due to the quasi-fission (QF) effect starts to show up. Comparing cross sections for the ER production and fission in reactions leading to the same CN, but having different values of entrance-channel mass-asymmetry, one can extract the fusion probability for a more symmetric combination with respect to quite an asymmetric one, where no limitation seems to occur. An attempt to find correlations between the fusion probabilities derived for the considered combinations and some entrance-channel characteristics is undertaken.

Multinucleon transfer reactions with $^{40}$Ca beams on closed shell nuclei $^{96}$Zr and $^{208}Pb at energies close to the Coulomb barrier were studied using magnetic spectrometers. The comparison between data and calculations, based on semiclassical models, allowed to identify the different degrees of freedom that influence the evolution of the reaction, like deformation, single, and pair transfer modes.