0000000001178730
AUTHOR
G. N. Knyazheva
showing 20 related works from this author
Asymmetric and symmetric fission of excited nuclei of Hg180,190 and Pb184,192,202 formed in the reactions with Ar36 and Ca40,48 ions
2021
Background: Observation of asymmetric fission of $^{180}\mathrm{Hg}$ has led to intensive theoretical and experimental studies of fission of neutron-deficient nuclei in the lead region.Purpose: The study of asymmetric and symmetric fission modes of $^{180,190}\mathrm{Hg}$ and $^{184,192,202}\mathrm{Pb}$ nuclei.Methods: Mass-energy distributions of fission fragments of $^{180,190}\mathrm{Hg}$ and $^{184}\mathrm{Pb}$ formed in the $^{36}\mathrm{Ar}+^{144,154}\mathrm{Sm}$ and $^{40}\mathrm{Ca}+^{144}\mathrm{Sm}$ reactions, respectively, at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET and compared with previously measured $^{192,20…
Fission dynamics: The quest of a temperature dependent nuclear viscosity
2013
This paper presents a journey within some open questions about the current use of a temperature dependent nuclear viscosity in models of nuclear fission and proposes an alternative experimental approach by using systems of intermediate fissility. This study is particularly relevant because: i) systems of intermediate fissility offer a suitable frame-work since the intervals between the compound nucleus and scission point temperatures with increasing excitation energy are much smaller than in the case of heavier systems, ii) the dependence of viscosity on the temperature may change with the fissility of the composite system; iii) the opportunity to measure also observables in the evaporation…
Fission and quasifission of composite systems with Z=108−120 : Transition from heavy-ion reactions involving S and Ca to Ti and Ni ions
2016
Background: Suppression of compound nucleus formation in the reactions with heavy ions by a quasifission process in dependence on the reaction entrance channel.
Fusion-fission and quasifission of superheavy systems withZ=110–116formed inCa48-induced reactions
2014
Background: In heavy-ion-induced reactions the mechanism leading to the formation of the compound nucleus and the role of quasifission is still not clear.Purpose: Investigation of the quasifission process of superheavy composite systems with $Z=110\text{\ensuremath{-}}116$ and comparison with properties of fusion-fission and quasifission of lighter composite systems.Method: Mass and energy distributions of fissionlike fragments formed in the reactions $^{48}\mathrm{Ca}+^{232}\mathrm{Th}$, ${}^{238}\mathrm{U}$, ${}^{244}\mathrm{Pu}$, and ${}^{248}\mathrm{Cm}$ at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the U-400 cyclotron…
The study of neutron-rich nuclei production in the region of the closed shell N=126 in the multi-nucleon transfer reaction 136Xe+208Pb
2015
Expérience LNL/PRISMA; International audience; The unexplored area of heavy neutron rich nuclei is extremely important for nuclearastrophysics investigations and, in particular, for the understanding of the r-process ofastrophysical nucleogenesis. For the production of heavy neutron rich nuclei located along theneutron closed shell N=126 (probably the last "waiting point" in the r-process of nucleosynthesis)the low-energy multi-nucleon transfer reaction 136Xe+208Pb at Elab=870MeV was explored.Due to the stabilizing eect of the closed neutron shells in both nuclei, N=82 and N=126, andthe rather favorable proton transfer from lead to xenon, the light fragments formed in this processare well b…
Energy loss of 132Xe-ions in thin foils
2009
Abstract The energy loss of 132Xe-ions in C, Al, Ni, Ag, Lu, Au, Pb and Th foils was measured in the energy range from 0.1 to 5 MeV/u using the TOF-E method. The results are compared with previously published data and with the predictions of several computer codes. They include theoretical codes: PASS, CASP, semi-empirical programs: SRIM, LET and the Hubert table predictions.
Is nuclear viscosity dependent on temperature?
2018
Nuclear viscosity is an indispensable ingredient of the nuclear fission collective dynamical models. It governs the exchange of energy between the collective variables and the thermal bath. Its dependence on the shape and temperature is a matter of controversy. By using systems of intermediate fissility we have demonstrated in a recent study that the viscosity parameters is larger for compact shapes, and decreases for larger deformations of the fissioning system, at variance with the conclusions of the statistical model modified to include empirically viscosity and time scales. In this contribution we propose an experimental scenario to highlight the possible dependence of the viscosity fro…
New experimental stopping power data of 4He, 16O, 40Ar, 48Ca and 84Kr projectiles in different solid materials
2018
Abstract New experimental data on energy loss of 4 He, 16 O, 40 Ar, 48 Ca and 84 Kr ions in thin, self-supporting foils of C, Al, Ni, Ag, Lu, Au, Pb and Th are presented. The measurements, using the TOF-E method, were done in a very broad energy range around the stopping power maximum; typically from 0.1 to 11 MeV/u. When available, the extracted stopping power values are compared with the previously published data. The overall agreement is good although a fair comparison is difficult as the covered energy range is much larger than in previous measurements. The small error bars and a broad coverage allowed us to test the predictions of theoretical codes: PASS, CasP, and semi-empirical progr…
Shell effects in damped collisions ofSr88withYb176at the Coulomb barrier energy
2014
This work is a study of the influence of shell effects on the formation of binary fragments in damped collision. We have investigated binary reaction channels of the composite system with $Z=108$ produced in the reaction $^{88}\mathrm{Sr}$${+}^{176}$Yb at an energy slightly above the Bass barrier (${E}_{\text{c.m.}}/{E}_{\text{Bass}}=1.03$). Reaction products were detected by using the two-arm time-of-flight spectrometer CORSET at the K130 cyclotron of the Department of Physics, University of Jyv\"askyl\"a. The mass-energy distribution of primary binary fragments has been measured. For targetlike fragments heavier than 190 u, which correspond to a mass transfer as large as twenty nucleons o…
Investigation of the reaction 64Ni+238U being an option of synthesizing element 120
2010
This study is concerned with the search for entrance channels suitable to synthesize elements with Z > 118. Mass-energy distributions as well as capture cross-sections of fission-like fragments have been measured for the reactions 64Ni + 238U → 302120 and 48Ca + 238U → 286112 at energies near the Coulomb barrier. Compound nucleus fission cross-sections were estimated from the analysis of mass and total kinetic energy distributions. The cross-section drops three orders of magnitude for the formation of the compound nucleus with Z = 120 obtained in the reaction 64Ni + 238U compared to the formation of the compound nucleus with Z = 112 obtained in the reaction 48Ca + 238U at an excitation ener…
Evidence of quasifission in the 180Hg composite system formed in the 68Zn + 112Sn reaction
2021
Abstract For the 68Zn + 112Sn reaction the Coulomb parameter Z 1 Z 2 is equal to 1500 that is close to the threshold value for the appearance of quasifission process. It was found that mass-energy distributions of the reaction fragments differ significantly from those obtained in the 36Ar + 144Sm reaction leading to the formation of the same composite system of 180Hg at similar excitation energies of about 50 MeV. In the case of the reaction with 68Zn ions, the mass distribution of fissionlike fragments has a wide two-humped shape with maximum yields at 70 and 110 u for the light and heavy fragments, respectively, instead of 80 and 100 u observed in the fission of 180Hg formed in the 36Ar +…
The fusion-fission process in the reaction 34S+186W near the interaction barrier
2014
International audience; The reaction 34S + 186W at Elab=160 MeV was investigated with the aim of diving into the features of thefusion-fission process. Gamma rays in coincidence with binary reaction fragments were measured using the high efficiencygamma-ray spectrometer ORGAM at the TANDEM Accelerator facility of I.P.N., Orsay, and the time-of-flight spectrometerfor fission fragments (FF) registration CORSET of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna. The couplingof the ORGAM and CORSET setups offers the unique opportunity of extracting details for characterizing the fusion-fissionprocess and gives information regarding production of neutron-rich heavy nuclei. The FF-$\gamm…
Fission and Quasi-Fission Dynamics Near the Coulomb Barrier: $\gamma$ Rays as Probe for their Timescale
2018
International audience; The overlap in the mass symmetric region of the reaction products from fusion-fission and quasi-fission complicates the assignment of symmetric events to complete fusion on the basis of the mass distribution alone. Additional observables, besides mass distribution, should be used. The method proposed here relies on the fact that fusion-fission and quasifission are characterized by a different timescale. Within this framework we performed a detailed study to find out if timescales can be probed via angular momentum as measured via γ rays multiplicity. The proof of principle was carried out by measuring the γ rays in coincidence with two fragments in the reaction 32S +…
Gamma rays as probe of fission and quasi-fission dynamics in the reaction 32S + 197Au near the Coulomb barrier
2017
International audience; Compound nucleus fission and quasi-fission are both binary decay channels whose common properties make the experimental separation between them difficult. A way to achieve this separation could be to probe the angular momentum of the binary fragments. This can be done detecting gamma rays in coincidence with the two fragments. As a case study, the reaction 32S + 197Au near the Coulomb barrier has been performed at the Tandem ALTO facility at IPN ORSAY. ORGAM and PARIS, two different gamma detectors arrays, are coupled with the CORSET detector, a two-arm time-of-flight spectrometer. TOF-TOF data were analyzed to reconstruct the mass-energy distribution of the primary …
Production of n-rich Nuclei along the Closed Shell N=126 in the collision 136Xe + 208Pb @E lab =870 MeV
2018
Multi-nucleon transfer reactions are nowadays the only known mean to produce neutron-rich nuclei in the Terra Incognita. The closed-shell region N=126 is crucial for both studying shell-quenching in exotic nuclei and the r-process, being its last "waiting-point". The choice of suitable reactions is challenging and a favorable case is 136Xe+208Pb, near the Coulomb barrier, because their neutron shell-closures play a stabilizing role, favoring the proton-transfer from lead to xenon. TOF-TOF data were analyzed to reconstruct the mass-energy distribution of the primary fragments. Preliminary results of an experiment held at Laboratori Nazionali di Legnaro with PRISMA, aimed at A and Z identific…
Fission of 180,182,183Hg* and 178Pt* nuclei at intermediate excitation energies
2022
Purpose: The study of asymmetric and symmetric fission of 180,182,183Hg and 178Pt nuclei as a function of their excitation energy and isospin. Methods: Mass-energy distributions of fission fragments of 180Hg, 178Pt (two protons less than 180Hg), and 182Hg (two neutrons more than 180Hg) formed in the 36Ar+144Sm,142Nd, and 40Ca+142Nd reactions were measured at energies near and above the Coulomb barrier. Fission of 183Hg obtained in the reaction of 40Ca with 143Nd was also investigated to see if one extra neutron could lead to dramatic changes in the fission process due to the shape-staggering effect in radii, known in 183Hg. The measurements were performed with the double-arm time-of-flight …
Asymmetric and symmetric fission of excited nuclei of 180,190Hg and 184,192,202Pb formed in the reactions with 36Ar and 40,48Ca ions
2021
Background: Observation of asymmetric fission of 180Hg has led to intensive theoretical and experimental studies of fission of neutron-deficient nuclei in the lead region. Purpose: The study of asymmetric and symmetric fission modes of 180,190Hg and 184,192,202Pb nuclei. Methods: Mass-energy distributions of fission fragments of 180,190Hg and 184Pb formed in the 36Ar+144,154Sm and 40Ca+144Sm reactions, respectively, at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET and compared with previously measured 192,202Pb isotopes produced in the 48Ca+144,154Sm reactions. The mass distributions for 180,190Hg and 184,192,202Pb together with…
Fusion-fission and quasifission of superheavy systems with Z=110-116 formed in Ca 48 -induced reactions
2014
Background: In heavy-ion-induced reactions the mechanism leading to the formation of the compound nucleus and the role of quasifission is still not clear. Purpose: Investigation of the quasifission process of superheavy composite systems with Z = 110-116 and comparison with properties of fusion-fission and quasifission of lighter composite systems. Method: Mass and energy distributions of fissionlike fragments formed in the reactions 48Ca +232 Th, 238U, 244Pu, and 248Cm at energies near the Coulomb barrier have been measured using the double-arm time-of-flight spectrometer CORSET at the U-400 cyclotron of the FLNR JINR. Results: The most probable fragment masses as well as total kinetic ene…
Investigation of fusion probabilities in the reactions with 52,54Cr, 64Ni, and 68Zn ions leading to the formation of Z = 120 superheavy composite sys…
2020
Background: The formation of superheavy nuclei in fusion reactions is suppressed by a competing quasifission process. The competition between the formation of the compound nucleus and the quasifission depends strongly on the reaction entrance channel. Purpose: The investigation of fission and quasifission processes in the formation of Z=120 superheavy composite systems in the 52,54Cr+248Cm and 68Zn+232Th reactions, and their comparison with the 64Ni+238U reaction at energies in the vicinity of the Coulomb barrier. Methods: Mass-energy distributions of fissionlike fragments formed in the reactions 52,54Cr+248Cm and 68Zn+232Th at energies near the Coulomb barrier were measured using the doubl…
Shell effects in damped collisions of Sr-88 with Yb-176 at the Coulomb barrier energy
2014
[Introduction] This work is a study of the influence of shell effects on the formation of binary fragments in damped collision. We have investigated binary reaction channels of the composite system with Z = 108 produced in the reaction 88 Sr + 176 Yb at an energy slightly above the Bass barrier ( E c.m. /E Bass = 1 . 03). Reaction products were detected by using the two-arm time-of-flight spectrometer CORSET at the K130 cyclotron of the Department of Physics, University of Jyv ̈ askyl ̈ a. The mass-energy distribution of primary binary fragments has been measured. For targetlike fragments heavier than 190 u, which correspond to a mass transfer as large as twenty nucleons or more, an enhance…