Search

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 .

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.

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.