Many observations strongly support the hypothesis that nuclei may fission through several independent fission modes (multimodal fission) interpreted as different prescission shapes and fission paths in a multidimensional potential energy landscape where shell effects are dominant. Mass distributions of the fission fragments are sensitive to the potential energy landscape and appear to be single humped (symmetric) or double humped (asymmetric). In many cases a mixture of both modes is observed. We propose here our study on 180Hg. Binary fission fragments formed in the reaction 68Zn + 112Sn → 180Hg at different excitation energies around the Coulomb barrier were detected using the double-arm time-of-flight technique with the spectrometers CORSET. The experiment was performed at JYFL (Jyvaskyla, Finland). We will discuss an analysis of the mass distributions in terms of fission modes predicted by a five-dimensional fission model. We have found out that the mass distributions can be well reproduced by considering a symmetric fission mode and two asymmetric modes at (AL ≈ 80, AH ≈ 100) and (AL ≈ 70 and AH ≈ 110).

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 nature of asymmetric fission of preactinides is not yet understood in detail, despite intense experimental and theoretical studies carried out at present.Purpose: The study of asymmetric and symmetric fission of $^{180,182,183}\mathrm{Hg}$ and $^{178}\mathrm{Pt}$ nuclei as a function of their excitation energy and isospin.Methods: Mass-energy distributions of fission fragments of $^{180}\mathrm{Hg}, ^{178}\mathrm{Pt}$ (two protons less than $^{180}\mathrm{Hg}$), and $^{182}\mathrm{Hg}$ (two neutrons more than $^{180}\mathrm{Hg}$) formed in the $^{36}\mathrm{Ar}+^{144}\mathrm{Sm}, ^{142}\mathrm{Nd}$, and $^{40}\mathrm{Ca}+^{142}\mathrm{Nd}$ reactions were measured at energies near and above the Coulomb barrier. Fission of $^{183}\mathrm{Hg}$ obtained in the reaction of $^{40}\mathrm{Ca}$ with $^{143}\mathrm{Nd}$ 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 $^{183}\mathrm{Hg}$.The measurements were performed with the double-arm time-of-flight spectrometer CORSET.Results: The observed peculiarities in the fission fragment mass-energy distributions for all studied nuclei may be explained by the presence of a symmetric fission mode and three asymmetric fission modes, manifested by the different total kinetic energies and fragment mass splits. The yield of symmetric mode grows with increasing excitation energy of compound nucleus.Conclusions: The investigated properties of asymmetric fission of $^{180,182,183}\mathrm{Hg}$ and $^{178}\mathrm{Pt}$ nuclei point out the existence of well-deformed proton shell at $Z\ensuremath{\approx}36$ and a less deformed proton shell at $Z$ \ensuremath{\approx} 46.

n Erratum to this paper has been published: https://doi.org/10.3103/S1062873822340019

An Erratum to this paper has been published: https://doi.org/10.3103/S1062873822340019

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.

Background: The nature of asymmetric fission of preactinides is not yet understood in detail, despite intense experimental and theoretical studies carried out at present. Purpose: The study of asymmetric and symmetric fission of Hg-180,Hg-182,Hg-183 and Pt-178 nuclei as a function of their excitation energy and isospin. Methods: Mass-energy distributions of fission fragments of Hg-180, Pt-178 (two protons less than Hg-180), and Hg-182 (two neutrons more than Hg-180) formed in the( 36)Ar+Sm-144, Nd-142, and Ca-40+Nd-142 reactions were measured at energies near and above the Coulomb barrier. Fission of Hg-183 obtained in the reaction of Ca-40 with Nd-143 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 Hg-183. The measurements were performed with the double-arm time-of-flight spectrometer CORSET. Results: The observed peculiarities in the fission fragment mass-energy distributions for all studied nuclei may be explained by the presence of a symmetric fission mode and three asymmetric fission modes, manifested by the different total kinetic energies and fragment mass splits. The yield of symmetric mode grows with increasing excitation energy of compound nucleus. Conclusions: The investigated properties of asymmetric fission of Hg-180,Hg-182,Hg-183 and Pt-178 nuclei point out the existence of well-deformed proton shell at Z approximate to 36 and a less deformed proton shell at Z approximate to 46.

The mass–energy distributions of binary fission fragments (FFs) of excited exotic nucleus 178 Pt* were measured via the fusion reaction 36 Ar + 142 Nd at different beam energies within 158–222 MeV range using the double arm time-of-flight spectrometer CORSET. The analysis of mass–energy matrices reveals the presence of both asymmetric and symmetric modes corresponding to respective lower and higher total kinetic energy (TKE) of the fragments within 42–64 MeV excitation energy. The agreement of measured mass width with theoretical systematics and dominance of the associated symmetric TKE component at 93 MeV excitation energy indicates the significant predominance/suppression of symmetric/asymmetric mode, respectively. The most probable light and heavy mass peaks of asymmetric fission mode of 178 Pt are spotted at 79 and 99 u, respectively. As inferred from the theory, the mass–TKE events observed at the highest measured excitation energy (93 MeV) endorse the presence of the fast-fission process in 178 Pt* at high angular momentum.

Asymmetric fission of mercury nuclei was initially observed in the low-energy region. In recent years, several experiments have been performed in this direction to investigate the asymmetric behaviour of Hg nuclei which supported the influence of shell effects on the asymmetric fission process. An experiment was performed using the CORSET setup. We investigated mass and energy distributions of fragments and fission characteristics of prolately-deformed Hg-182 and oblately-deformed Hg-183 nuclei formed in the Ca-40+Nd-142,Nd-143 reactions at three different beam energies - E-lab = 172, 192, and 212 MeV. We found no huge variation in mass-energy distributions of Hg-182 and Hg-183 at any of the measured energies. This gives us an outlook regarding the influence of shell structure, charge radii deformation, and factors associated with the potential energy surface that is responsible for fission in the Hg region.

A study is performed of the asymmetric fission of neutron-deficient mercury 180, 190 Hg isotopes obtained in the reactions of 36 Ar + 144, 154 Sm and 68 Zn + 112 Sn at incident energies near and above the Coulomb barrier. The relative contributions from asymmetric and symmetric fission change along with the excitation energy of the fissile compound nucleus. The effect the characteristics of the entrance channel have on the dynamics of the reaction is studied.

Background: Observation of asymmetric fission of Hg-180 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 Hg-180,Hg-190 and Pb-184,Pb-192,Pb-202 nuclei. Methods: Mass-energy distributions of fission fragments of Hg-180,Hg-190 and Pb-184 formed in the Ar-36 + Sm-144,Sm-154 and Ca-40+ Sm-144 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 Pb-192,Pb-202 isotopes produced in the Ca-48(+) Sm-144,Sm-154 reactions. The mass distributions for Hg-180,Hg-190 and Pb-184,Pb-192,Pb-202 together with old data for Ir-187, Au-195, Hg-198, Tl-201, Bi-205,Bi-207, Po-210, and At-213 [J. Nucl. Phys. 53, 1225 (1991)] have been decomposed into symmetric and asymmetric fission modes. The total kinetic-energy distributions for different fission fragment mass regions have been analyzed for Hg-180,Hg-190 and Pb-184. Results: The stabilization role of proton numbers at Z approximate to 36, 38, Z approximate to 45, 46, and Z = 28/50 in asymmetric fission of excited preactinide nuclei has been observed. The high (approximate to 145-MeV) and the low (approximate to 128-MeV) energy components have been found in the total kinetic-energy distributions of Hg-180,Hg-190 fission fragments corresponding to the fragments with proton numbers near Z approximate to 46 and Z approximate to 36, respectively. In the case of fission of Pb-184 only the low-energy component (approximate to 135MeV) for the fragments with masses corresponding to the proton numbers Z approximate to 36 and 46 has been found. Conclusions: The studied properties of asymmetric fission of Hg-180,Hg-190 and Pb-184,Pb-192,Pb-202 nuclei point out the existence of well deformed proton shell at Z approximate to 36 and less deformed proton shell at Z approximate to 46.

The mass-energy distributions of fragments of the reaction 32 S + 232 Th leading to the formation of 264 Sg ( Z = 106) at energies of incident ions 32 S of 165, 181 and 200 MeV are measured. The contribution from the quasifission process is found at energies below and above the Coulomb barrier in the region of symmetric masses ( А CN /2 ± 20). A high-energy symmetric fission mode is found at an energy of 165 MeV, which corresponds to the excitation energy of the compound 264 Sg nucleus 45 MeV.

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.

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 double-arm time-of-flight spectrometer CORSET. Results: Capture cross sections for the reactions under investigation were measured. The most probable fragment masses and total kinetic energies as well as their variances in dependence on the interaction energy were studied for asymmetric and symmetric fragments. The fusion probabilities were estimated from the analysis of mass-energy distributions. Conclusions: The estimated fusion probability drops down by a factor of 103 in the 54Cr+248Cm reaction compared to the reactions of 48Ca ions with actinides. Among the studied reactions, the 54Cr+248Cm is the most favorable one for the production of the superheavy element with Z=120.1 MoreReceived 3 August 2020Accepted 2 September 2020DOI:https://doi.org/10.1103/PhysRevC.102.044605©2020 American Physical SocietyPhysics Subject Headings (PhySH)FissionResearch AreasEnergy sourcesNuclear powerFissionResearch AreasNuclear reactionsFissionResearch AreasFissionLow & intermediate energy heavy-ion reactionsNuclear fusionPropertiesA ≥ 220Nuclear Physics

The mass, energy and angular distributions of binary fragments formed in the reactions 64Ni + 238U, 58Fe + 244Pu, 52Cr + 248Cm, 54Cr + 248Cm at energies near the Coulomb barrier have been measured. The analysis of energy distributions of the symmetric fragments with mass numbers $${{{{A}_{{{\text{CN}}}}}} \mathord{\left/ {\vphantom {{{{A}_{{{\text{CN}}}}}} 2}} \right. \kern-0em} 2} \pm 20$$ formed in these reactions have been applied to separate compound nucleus fission and quasi-fission. The estimated fusion probability for the reactions Cr, Fe, and Ni ions with actinide targets shows an exponential dependence on the mean fissility parameter of the system and shows also that reaction with Cr ions is more favorable for production of the super heavy element with Z = 120.

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 Cr-52,Cr-54 + Cm-248 and Zn-68+ Th-232 reactions, and their comparison with the Ni-64+ U-238 reaction at energies in the vicinity of the Coulomb barrier. Methods: Mass-energy distributions of fissionlike fragments formed in the reactions Cr-52,Cr-54 + Cm-248 and Zn-68+ Th-232 at energies near the Coulomb barrier were measured using the double-arm time-of-flight spectrometer CORSET. Results: Capture cross sections for the reactions under investigation were measured. The most probable fragment masses and total kinetic energies as well as their variances in dependence on the interaction energy were studied for asymmetric and symmetric fragments. The fusion probabilities were estimated from the analysis of massenergy distributions. Conclusions: The estimated fusion probability drops down by a factor of 10(3) in the Cr-54 + Cm-248 reaction compared to the reactions of Ca-48 ions with actinides. Among the studied reactions, the Cr-54 + Cm-248 is the most favorable one for the production of the superheavy element with Z = 120.