Asymmetric And Symmetric Fission Of Excited Nuclei Of Hg-180,Hg-190 And Pb-184,Pb-192,Pb-202 Formed In The Reactions With Ar-36 And Ca-40,Ca-48 Ions

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.