Measurements of the t-t and p-t coincidence events in the $^3$H ($alpha$, ttp) reaction have been obtained at $E_alpha$ incident energy of 67.2 MeV. Various appropriate angular configurations of detectors were chosen in order to observe the populatio
n of the $^6$He$^*$ state at around 18 MeV. Its contribution appears at the $E_{rm tt}$ relative energy of 6.0 MeV by the analysis of bidimensional spectra. We found the formation of the $^6$He excited state at $E^* = 18.3 pm 0.2$ MeV (with a $Gamma$ width of 1.1 $pm$ 0.3 MeV) by the decay into the t+t binary channel, since the threshold energy of the t+t channel is 12.31 MeV. In each analyzed bidimensional energy spectrum of ($E_{rm t}$, $E_{rm t}$) and ($E_{rm p}$, $E_{rm t}$) coincidence events resonance structures are present due to the formation of both $^6$He$^*$ and $^4$He$^*$ excited states. Our results on the $E^*$ and $Gamma$ values regarding the $^6$He$^*$ level of about 18 MeV are compared with the results obtained by other reactions. Moreover, we also found new $Gamma$ width values of 0.7 $pm$ 0.3 and 0.8 $pm$ 0.4 MeV for the 14.0 $pm$ 0.4 and 16.1 $pm$ 0.4 MeV $^6$He levels, respectively.
The $^3$H+$^3$He cluster structure in $^6$Li was investigated by the $^3$H($alpha$,$^3$H $^3$He)n kinematically complete experiment at the incident energy $E_alpha$ = 67.2 MeV. We have observed two resonances at $E_x^*$ = 21.30 and 21.90 MeV which ar
e consistent with the $^3$He($^3$H, $gamma$)$^6$Li analysis in the Ajzenberg-Selove compilation. Our data are compared with the previous experimental data and the RGM and CSRGM calculations.
The fusion excitation function is the important quantity in planning experiments for the synthesis of superheavy elements. Its values seem to be determined by the experimental study of the hindrance to complete fusion by the observation of mass, angu
lar and energy distributions of the fissionlike fragments. There is ambiguity in establishment of the reaction mechanism leading to the observed binary fissionlike fragments. The fissionlike fragments can be produced in the quasifission, fast fission, and fusion-fission processes which have overlapping in the mass (angular, kinetic energy) distributions of fragments. The branching ratio between quasifission and complete fusion strongly depends on the characteristics of the entrance channel. In this paper we consider a wide set of reactions (with different mass asymmetry and mass symmetry parameters) with the aim to explain the role played by many quantities on the reaction mechanisms. We also present the results of study of the $^{48}$Ca+$^{249}$Bk reaction used to synthesize superheavy nuclei with Z = 117 by the determination of the evaporation residue cross sections and the effective fission barriers $<B_{rm f}>$ of excited nuclei formed along the de-excitation cascade of the compound nucleus.
