0000000000583470
AUTHOR
E.v. Prasad
Zeptosecond contact times for element Z=120 synthesis
The synthesis of new superheavy elements beyond oganesson (Z=118) requires fusion reactions with projectile nuclei with proton numbers larger than that of $^{48}$Ca (Z=20), which has been successfully employed for the synthesis of elements with Z=112-118. In such reactions, fusion is drastically hindered by fast non-equilibrated dynamical processes. Attempts to produce nuclei with Z=120 using the $^{64}$Ni+$^{238}$U, $^{58}$Fe+$^{244}$Pu, $^{54}$Cr+$^{248}$Cm, and $^{50}$Ti+$^{249}$Cf reactions have been made, which all result in larger Coulomb forces than for $^{48}$Ca-induced reactions, but no discovery has been confirmed to date. In this work, mass and angle distributions of fission frag…
Nuclear structure dependence of fusion hindrance in heavy element synthesis
The production of the heaviest elements in fusion-evaporation reactions is substantially limited by very low cross sections, as fusion cross sections (including fusion-fission) are greatly reduced by the competing quasifission mechanism. Using the Australian National University Heavy Ion Accelerator Facility and CUBE detector array, fission fragments from the $^{48}\mathrm{Ti}+^{204,208}\mathrm{Pb}$ and $^{50}\mathrm{Ti}+^{206,208}\mathrm{Pb}$ reactions have been measured, with the aim to investigate how the competition between quasifission and fusion-fission evolves with small changes in entrance-channel properties associated mainly with the nuclear structure. Analysis of mass-distribution…
Quasifission in heavy and superheavy element formation reactions
Superheavy elements are created in the laboratory by the fusion of two heavy nuclei. The large Coulomb repulsion that makes superheavy elements decay also makes the fusion process that forms them very unlikely. Instead, after sticking together for a short time, the two nuclei usually come apart, in a process called quasifission. Mass-angle distributions give the most direct information on the characteristics and time scales of quasifission. A systematic study of carefully chosen mass-angle distributions has provided information on the global trends of quasifission. Large deviations from these systematics reveal the major role played by the nuclear structure of the two colliding nuclei in de…
Observation of mass-asymmetric fission of mercury nuclei in heavy ion fusion
Background: Mass-asymmetric fission has been observed in low energy fission of $^{180}\mathrm{Hg}$. Calculations predicted the persistence of asymmetric fission in this region even at excitation energies of 30--40 MeV.Purpose: To investigate fission mass distributions by populating different isotopes of Hg using heavy ion fusion reactions.Methods: Fission fragment mass-angle distributions have been measured for two reactions, $^{40}\mathrm{Ca}+^{142}\mathrm{Nd}$ and $^{13}\mathrm{C}+^{182}\mathrm{W}$, populating $^{182}\mathrm{Hg}$ and $^{195}\mathrm{Hg}$, respectively, using the Heavy Ion Accelerator Facility and CUBE spectrometer at the Australian National University. Measurements were ma…
Mechanisms Suppressing Superheavy Element Yields in Cold Fusion Reactions.
Superheavy elements are formed in fusion reactions which are hindered by fast nonequilibrium processes. To quantify these, mass-angle distributions and cross sections have been measured, at beam energies from below-barrier to 25% above, for the reactions of $^{48}\mathrm{Ca}$, $^{50}\mathrm{Ti}$, and $^{54}\mathrm{Cr}$ with $^{208}\mathrm{Pb}$. Moving from $^{48}\mathrm{Ca}$ to $^{54}\mathrm{Cr}$ leads to a drastic fall in the symmetric fission yield, which is reflected in the measured mass-angle distribution by the presence of competing fast nonequilibrium deep inelastic and quasifission processes. These are responsible for reduction of the compound nucleus formation probablity ${P}_{CN}$ …