Fission and Quasi-Fission in Reactions with Deformed Nuclei
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ion and Quasi-Fission in Reactions with Deformed Nuclei Yu. M. Itkisa, *, A.V. Karpova, G. N. Knyazhevaa, E. M. Kozulina, N. I. Kozulinaa, K. V. Novikova, K. B. Gikala, I. N. Diatlova, I. V. Pchelintseva, I. V. Vorobiova, A. N. Pana, b, and P. P. Singhc aJoint
Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia bInstitute of Nuclear Physics, Almaty, 050032 Kazakhstan c Indian Institute of Technology Ropar, Rupnagar, Punjab, 140001 India *e-mail: [email protected] Received March 2, 2020; revised April 15, 2020; accepted April 27, 2020
Abstract—The mass-energy distributions of fragments formed in reactions 16,18O + 232Th, 238U, and 22Ne + 232Th, 238U at energies near the Coulomb barrier are measured to study the role of multimodal fission in the reactions of light ions with strongly deformed actinide nuclei. It is found that at these energies, multimodal fission affects significantly the mass–energy and angular distributions of fragments that results in an increase of the width of mass distributions and large angular anisotropy as in the case of quasifission. DOI: 10.3103/S1062873820080158
INTRODUCTION In collisions between strongly deformed nuclei, their mutual orientation has a substantial impact on the reaction dynamics. Analysis of the mass–energy and angular distributions of fragments shows that at energies near and below the Coulomb barrier, a considerable contribution from the quasi-fission process to the capture cross section of the reaction is observed in reactions between 40, 48Са ions and strongly deformed isotopes 152, 154Sm, while no quasi-fission is detected for reactions with spherical 144Sm nuclei [1]. The dynamics of the reactions between such light ions as C, O, F, Ne, and actinide nuclei has been widely studied by many scientific groups. Abnormally high values obtained experimentally for the angular anisotropy of fragments [2] and an increase in the dispersion of mass distributions [3] in the sub-barrier region have been explained by manifestation of the quasi-fission process caused by orientation effects in reactions with deformed nuclei. An abnormally high anisotropy of fragments at sub-barrier energies of interaction was detected for the first time in the reaction between 16O and deformed 238U nuclei. Cross sections of the formation of evaporative residue were also measured for this reaction at energies above and below the barrier [4]. Calculations using a statistical model with allowance for the deformation of 238U reproduced the obtained experimental cross sections. The analysis of evaporative residues performed in [4] thus showed there was no suppression of the fusion channel in the sub-barrier region. And therefore, high angular anisotropy and an enhanced width of the mass distribution of fragments
are not the reasons to expect the presence of the orientation-dependent quasi-fission for this system. Considerably high experimental values of the angular anisotropy of asymmetrically divided fragments were observed in radiochemical measurements of the angular distributions of fiss
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