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Register a new useralpha-particle production in the scattering of 6He by 208Pb at energies around the Coulomb barrier
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New experimental data from the scattering of 6He+208Pb at energies around and below the Coulomb barrier are presented. The yield of breakup products coming from projectile fragmentation is dominated by a strong group of $alpha$ particles. The energy and angular distributions of this group have been analyzed and compared with theoretical calculations. This analysis indicates that the $alpha$ particles emitted at backward angles in this reaction are mainly due to two-neutron transfer to weakly bound states of the final nucleus.
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New experimental results for the elastic scattering of 6He on 64Zn at incident energies of 15.0 and 18.0 MeV and 4He at 17.5 MeV along with results already published at 10.0 and 13.6 MeV, are presented. Elastic and alpha experimental cross sections are compared with coupled-reaction-channel, continuum-discretized coupledchannel, and DWBA inclusive-breakup models. The large yield of alpha particles observed at all measured energies can be explained by considering a nonelastic breakup mechanism.
The $gamma$ process in supernova explosions is thought to explain the origin of proton-rich isotopes between Se and Hg, the so-called $p$ nuclei. The majority of the reaction rates for $gamma$ process reaction network studies has to be predicted in Hauser-Feshbach statistical model calculations using global optical potential parameterizations. While the nucleon+nucleus optical potential is fairly known, for the $alpha$+nucleus optical potential several different parameterizations exist and large deviations are found between the predictions calculated using different parameter sets. By the measurement of elastic $alpha$-scattering angular distributions at energies around the Coulomb barrier a comprehensive test for the different global $alpha$+nucleus optical potential parameter sets is provided. Between 20$^{circ}$ and 175$^{circ}$ complete elastic alpha scattering angular distributions were measured on the $^{113}$In textit{p} nucleus with high precision at E$_{c.m.}$ = 15.59 and 18.82 MeV. The elastic scattering cross sections of the $^{113}$In($alpha$,$alpha$)$^{113}$In reaction were measured for the first time at energies close to the astrophysically relevant energy region. The high precision experimental data were used to evaluate the predictions of the recent global and regional $alpha$+nucleus optical potentials. Parameters for a local $alpha$+nucleus optical potential were derived from the measured angular distributions. Predictions for the reaction cross sections of $^{113}$In($alpha,gamma$)$^{117}$Sb and $^{113}$In($alpha$,n)$^{116}$Sb at astrophysically relevant energies were given using the global and local optical potential parameterizations.
The complete and incomplete fusion cross sections for $^{7}$Li+$^{124}$Sn reaction were measured using online and offline characteristic $gamma$-ray detection techniques. The complete fusion (CF) cross sections at energies above the Coulomb barrier were found to be suppressed by $sim$ 26 % compared to the coupled channel calculations. This suppression observed in complete fusion cross sections is found to be commensurate with the measured total incomplete fusion (ICF) cross sections. There is a distinct feature observed in the ICF cross sections, i.e., $textit{t}$-capture is found to be dominant than $alpha$-capture at all the measured energies. A simultaneous explanation of complete, incomplete and total fusion (TF) data was also obtained from the calculations based on Continuum Discretized Coupled Channel method with short range imaginary potentials. The cross section ratios of CF/TF and ICF/TF obtained from the data as well as the calculations showed the dominance of ICF at below barrier energies and CF at above barrier energies.
In this work, angular distribution measurements for the elastic channel were performed for the 9Be+12C reaction at the energies ELab=13.0, 14.5, 17.3, 19.0 and 21.0 MeV, near the Coulomb barrier. The data have been analyzed in the framework of the double folding S~ao Paulo potential. The experimental elastic scattering angular distributions were well described by the optical potential at forward angles for all measured energies. However, for the three highest energies, an enhancement was observed for intermediate and backward angles. This can be explained by the elastic transfer mechanism. Keywords: 9Be+12C, Elastic Scattering, S~aoo Paulo Potential.
The present understanding of reaction processes involving light unstable nuclei at energies around the Coulomb barrier is reviewed. The effect of coupling to direct reaction channels on elastic scattering and fusion is investigated, with the focus on halo nuclei. A list of definitions of processes is given, followed by a review of the experimental and theoretical tools and information presently available. The effect of couplings on elastic scattering and fusion is studied with a series of model calculations within the coupled-channels framework. The experimental data on fusion are compared to bare no-coupling one-dimensional barrier penetration model calculations. On the basis of these calculations and comparisons with experimental data, conclusions are drawn from the observation of recurring features. The total fusion cross sections for halo nuclei show a suppression with respect to the bare calculations at energies just above the barrier that is probably due to single neutron transfer reactions. The data for total fusion are also consistent with a possible sub-barrier enhancement; however, this observation is not conclusive and other couplings besides the single-neutron channels would be needed in order to explain any actual enhancement. We find that a characteristic feature of halo nuclei is the dominance of direct reactions over fusion at near and sub-barrier energies; the main part of the cross section is related to neutron transfers, while calculations indicate only a modest contribution from the breakup process.
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