Publications (71)86.79 Total impact

Article: Fission and quasifission modes in heavyioninduced reactions leading to the formation of Hs^{*}
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ABSTRACT: Mass and energy distributions of binary reaction products obtained in the reactions 22Ne+249Cf,26Mg+248Cm, 36S+238U, and 58Fe+208Pb have been measured. All reactions lead to Hs isotopes. At energies below the Coulomb barrier the bimodal fission of Hs*, formed in the reaction 26Mg+248Cm, is observed. In the reaction 36S+238U, leading to the formation of a similar compound nucleus, the main part of the symmetric fragments arises from the quasifission process. At energies above the Coulomb barrier fusionfission is the main process leading to the formation of symmetric fragments for both reactions with Mg and S ions. In the case of the 58Fe+208Pb reaction the quasifission process dominates at all measured energies.  [Show abstract] [Hide abstract]
ABSTRACT: Mass and energy distributions of fragments from fission of target nuclei 232Th and 235U induced by the 10.3–30.0 MeV protons have been measured with surfacebarrier silicon detectors. A new method for decomposition of experimental distributions into fragment mass and energy yields of four independent fission modes has been proposed. Main characteristics of fission modes such as distinct mode mass yields, mean masses and kinetic energies as well as variances in fragment masses and energies have been studied in relation with energy of protons. Revealed regularities in these quantities for given energy range of incident protons support the assumption that the modes S1 and S2 are initially formed in a unified asymmetric fission valley.  [Show abstract] [Hide abstract]
ABSTRACT: The massenergy distributions of fragments originating from the fission of the compound nucleus 226Th and their correlations with the multiplicity of γrays emitted from these fragments are measured and analyzed in 18O + 208Pb interaction induced by projectile oxygen ions of energy in the range Elab = 78198.5 MeV. Manifestations of an asymmetric fission mode, which is damped exponential with increasing Elab, 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 γrays 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. 
Article: The 226Th fission valleys
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ABSTRACT: One of the interesting problems in the nuclear fission studies is the nature of the asymmetry of the fission fragment mass distribution (FFMD). In connection with recent experiments, the valleys on the potential energy surface of 226Th have been considered. The prescission nuclear shape calculated as a result of the minimization in multidimensional space of the deformation parameters with two constrains is shown to be of the type considered by Brosa et al.  [Show abstract] [Hide abstract]
ABSTRACT: Results of the experiments aimed at the study of fission and quasifission processes in the reactions 36S+238U, 48Ca+144,154Sm, 168Er, 208Pb, 238U, 244Pu, 248Cm; 50Ti+208Pb, 244Pu;58Fe+208Pb, 244Pu, 248Cm, and 64Ni+186W, 242Pu leading to the formation of heavy and superheavy systems with Z=82122 are presented. Cross sections, massenergy and angular distributions for fission and quasifission fragments have been studied at energies close and below the Coulomb barrier. The influence of the reaction entrance channel properties as mass asymmetry, deformations and neutron excess, shell effects in the interacting nuclei and producing compound nucleus the mechanism of the fusionfission and the competitive process of quasifission are discussed.  [Show abstract] [Hide abstract]
ABSTRACT: The massenergy 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 twocomponent analysis of the dependence Mγ(M) shows that the asymmetric mode survives in fission only at low partialwave orbital angular momenta of compound nuclei. It is found that, for all E lab, the gammaray 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.  [Show abstract] [Hide abstract]
ABSTRACT: Massenergy distributions (MEDs) and capturefission cross sections have been measured in the reaction Ca48 + Pb208 > No256 at the energies Elab = 206242 MeV using a doublearm timeofflight spectrometer CORSET. It has been observed that MED of the fragments consists of two parts, namely, the classical fusionfission process corresponding to the symmetric fission of 256No and quasifission "shoulders" corresponding to the light fragment masses similar to 6090 u and complimentary heavy fragment masses. The quasifission "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 fusionfission and quasifission components. In the fusionfission process a highenergy SuperShort mode has been discovered for the masses MH = 130135 u and the TKE of approximate to 233 MeV.  [Show abstract] [Hide abstract]
ABSTRACT: Massenergy distributions (MEDs) and capturefission cross sections have been measured in the reaction 48Ca + 208Pb → 256No at the energies Elab=206–242 MeV using a doublearm timeofflight 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 256No and quasifission “shoulders” corresponding to the light fragment masses ∼60–90 u and complimentary heavy fragment masses. The quasifission “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 quasifission components. In the fusion–fission process a highenergy SuperShort mode has been discovered for the masses MH=130–135 u and the TKE of ≈233 MeV.  [Show abstract] [Hide abstract]
ABSTRACT: New systematics have been developed for calculating the mass yields from the fission of actinide nuclei between Th and Bk, induced by protons and neutrons with kinetic energies in the range 5–200MeV. The systematics reproduce the experimental data accurately and are applicable as a basis for calculating independent fission fragment yields when the minor actinide transmutation in Accelerator–Driven Systems and other practical applications are of interest.  [Show abstract] [Hide abstract]
ABSTRACT: Correlations between folding angular distributions of fission fragments and the gammaray 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 completeand incompletefusion 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 incompletefusion process, folding angular distributions of fission fragments have a twocomponent 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 linearmomentum 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.  [Show abstract] [Hide abstract]
ABSTRACT: 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 threedimensional 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 linearresponse theory. 

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ABSTRACT: The neutron spectra associated to the two fission modes of 226Th have been measured in coincidence with the fragment yields of the 18O + 208Pb reaction at Elab = 78 MeV. The pre and postfission 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.  [Show abstract] [Hide abstract]
ABSTRACT: 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*≈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 64 Ni 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 64 Ni 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.  [Show abstract] [Hide abstract]
ABSTRACT: 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 Elab=28.5–62.5 MeV. The values of the ratio between the complete and incomplete fusion crosssections 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 crosssection is only ∼27% at the lithium projectile energy Elab=28.5 MeV (∼2 MeV below the Coulomb barrier).  [Show abstract] [Hide abstract]
ABSTRACT: The work presents the results of the study of characteristics of the neutron emission in fission and quasifission of heavy and superheavy nuclei, produced in the reactions with heavy ions. These experiments have been performed at the U400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR), tandem accelerator in Legnaro (LNL) and VIVITRON accelerator in Strasbourg (IReS) with the use of the timeofflight spectrometer of fission fragments CORSET and neutron multidetector DEMON. Massenergy distributions (MED) of the 48Ca + 168Er, 208Pb, 238U and 18O + 208Pb reactions products at energies close to and below the Coulomb barrier have been studied. The pre and postfission neutron multiplicities as a function of the fragment mass have been obtained. A significant yield of the asymmetric component observed in the fragment mass distributions in the case of 18O + 208Pb reaction denotes the multimodal nature of the fission process. At the same time an increase in the yield of fragment masses ML ≅ 7585 and MH ≅ 200210 in the case 48Ca+208Pb, 238U reactions and ML ≅ 7585 and MH ≅ 130140 in the case 48Ca+168Er is rather connected with a quasifission process. The obtained neutron multiplicities dependences on fragment masses showed the validity of these assumptions.  [Show abstract] [Hide abstract]
ABSTRACT: The massenergy distributions of the fragments, fusionfission (σFF) and capture (σcap) crosssections in the reactions 26Mg+248Cm; 48Ca+208Pb, 232Th, 238U, 244Pu, 248Cm; 58Fe+208Pb, 232Th, 244Pu, 248Cm were measured at the U400 accelerator of Flerov Laboratory of Nuclear Reactions (JINR, Russia) with use of doublearm timeofflight spectrometer CORSET. The influence of reaction entrance channel on the competition between fusionfission and quasifission processes was studied. Strong manifestation of the shell effects in mass distributions of fusionfission and quasifission fragments was observed. The multimodal fission phenomena were found for 274Hs and 256No nuclei at low excitation energies.  [Show abstract] [Hide abstract]
ABSTRACT: Results of the experiments aimed at the study of fission and quasifission processes in the reactions12C+204Pb,48Ca+144,154Sm,168Er,208Pb,244Pu,248Cm;58Fe+208Pb,244Pu,248Cm, and64Ni+186W,242Pu are presented in the work. The choice of the abovementioned reactions was inspired by recent experiments on the production of the isotopes283112,289114 and283116 at Dubna [1],[2] using the same reactions. The58Fe and64Ni projectiles were chosen since the corresponding projectiletarget combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U400 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 timeofflight spectrometer of fission fragments CORSET[3] and the neutron multidetector DEMON[4],[5]. The role of shell effects and the influence of the entrance channel on the mechanism of the compound nucleus fusionfission and the competitive process of quasifission are discussed. 
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567  Citations  
86.79  Total Impact Points  
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Institutions

19982011

National Nuclear Center of the Republic of Kazakhstan
Konechnaya, Pavlodar, Kazakhstan


19982007

Joint Institute for Nuclear Research
 Flerov Laboratory of Nuclear Reactions
Dubno, Moskovskaya, Russia


19842004

Institute of Nuclear Physics
Almaty, Almaty Qalasy, Kazakhstan
