Rocco Palamara

Entrance channel effect on the formation of heavy and superheavy nuclei

We study the effect of the entrance channel and the shell structure of reacting massive nuclei on the fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei. In the framework of the combined dinuclear system concept and advanced statistical model, we analyze the 40 Ar + 176 Hf, 86 Kr + 130 Xe and 124 Sn + 92 Zr reactions leading to 216 Th * ; the 32 S + 182 W, 48 Ti + 166 Er, and 60 Ni + 154 Sm reactions leading to 214 Th * ; the 40 Ar + 181 Ta reaction leading to 221 Pa * ; the 48 Ca + 248 Cm reaction leading to the 296 116 compound nucleus. In our calculations of the excitation functions for capture, fusion and evaporation residues we use the relevant variables such as mass-asymmetry of nuclei in the entrance channel, relative distance between nuclear centers, shell effect and shape of colliding nuclei and such characteristics of the reaction mechanism as potential energy surface, driving potential, the dependence of capture, fusion cross sections and survival probabil...

On the Broad First Excited 5He State

The reaction 7 Li( d , αα) n was studied by detecting αα coincidences with a forward-forward and a forward-backward geometry at 1.4, 2.1 and 2.5 MeV incident deuteron energies. The analysis of the αα bidimensional spectra allowed us to isolate the first excited 5 He state from other reaction products. The values of (3.8±0.3) MeV and of (3.1±0.5) MeV for the excitation energy and width of this state were found, respectively.

Experimental evidence of shell effects in the fission time of heavy nuclei

The crystal blocking technique has been used to measure delay times in the fission channel for excited nuclei produced in the 28 Si+ n a t Pt reaction. Experimental results range from 10 -17 to 10 -18 s at bombarding energies from 140 to 170 MeV. It is shown that fission barriers keep their double-humped structure for nuclear temperature up to 1.7–1.8 MeV, and that the lifetimes of excited states in the second potential well contribute essentially to the observed delay times in the fission channel.

The short-lived 8Be level at Ex=11.4 MeV

Measurements of the differential cross section for the 7Li(d, alpha alpha n) reaction have been performed at incident deuteron energy Ed=19.7 MeV. An appropriate kinematical configuration was chosen to observe the population of the second excited 8Be level. The values of (11.3+or-0.2) MeV for the excitation energy and of (3.7+or-0.2) MeV for the width of the above level were found. The influence of the transformation Jacobian on the determination of the two spectroscopic parameters is discussed.

Spectroscopic parameters of theJπ=1+,T=0 excited6Li level

An analysis of thed-α coincidence spectra of the7Li(3He, αd)4He reaction at incident energy of 5.0 MeV and at various detector angles has been carried out. The values of the spectroscopic parameters of theJπ=1+,T=06Li state at excitation energy of 5.65 MeV have been deduced. The results, considering the experimental errors, do not appear to be dependent on the geometry and are in line with the ones adopted in literature.

Synthesis of Heavy and Superheavy Elements by Reactions of Massive Nuclei

By comparing theoretical and experimental excitation functions of evaporation residues resulting from the same compound nucleus or heavy and superheavy nuclei, it is possible to understand the effect of the entrance channel and the shell structure of reacting nuclei on the fusion mechanism. The competition of complete fusion with the quasifission process is strongly related to the intrinsic fusion barrier Bfus* and the quasifission barrier Bqf as well as the size of the well in the nucleus-nucleus potential. In our calculations of the excitation functions for capture, fusion, and evaporation residues, we use the relevant variables such as mass asymmetry of nuclei in the entrance channel, potential energy surface, driving potential, spin distribution, and surviving probability of compound nucleus that are responsible for the mechanism of the fusion-fission process. As a result, we obtain a beam energy window for the capture of the nuclei before the system fuses and the Γn/Γf ratio at each step along the deexcitation cascade of the compound nucleus. Calculations performed in the framework of the model taking into account the nuclear shell effect and shape of colliding nuclei allow us to reach useful conclusions about the mechanism of the fusion-fission process and the production of the evaporation residues. We analyze the 40Ar + 176Hf, 86Kr + 130Xe, and 124Sn + 92Zr reactions leading to 216Th*; the 32S + 182W and 60Ni + 154Sm reactions leading to 214Th*; the 48Ca + 248Cm reaction leading to the 296116 compound nucleus; and the 48Ca + 249Cf reaction leading to the 297118 compound nucleus.

5He energy spectrum analysis by the7Li(d, αn)α reaction

SummaryThe7Li(d, αn)α kinematically complete experiment atEd=0.85 and 1.15 MeV has been performed. Each5He asymmetric energy spectrum obtained was fitted by an inchoerent sum of the contributions coming from the ground state and from the first excited state of the same nucleus. The result, compared with the single-levelR-matrix calculations, shows that the asymmetric shape of the experimental energy spectrum cannot be interpreted as an intrinsic property only of the5He ground state but it is also due to the contribution of the low-energy tail of the first excited state of the same nucleus.