The ? Clustering Effects In Fusion-evaporation Reactions Between Light-heavy Ions

The fusion-evaporation reaction is a very important reaction process in nuclear astrophysics,which provides a significant source for star burning and stellar nucle-osynthesis.Because of the high-efficient energy output and abundant materials in the nature,it is a very promising way for the utilization of new energy in the future.The experimental phenomenon in nuclear reactions is essentially a representation of the in-ternal properties of the nuclear structures.Considering that the?-cluster structures are well established in most of light-heavy nuclei,it is very attractive to study the role of?clustering effects in the fusion-evaporation reaction between light-heavy ions.In this thesis,we firstly introduce the history of the nuclear reaction,and the back-ground of the researches in the fusion-evaporation reaction and the nuclear structure models.The discrepancies between the theoretical results from the statistical model and the experimental data are specified.Then we introduce the statistical model of the fusion-evaporation reaction in detail,from the Bohr independence hypothesis to the Weisskopf theory of evaporation then to the Hauser-Feshbach statistical model.The energy level density and the transmission coefficient which are two critical quantities in the model are emphasized.At energies near the Coulomb barrier,we study the^18,16O+^13,12C fusion-evaporation reactions.In order to resolve the underestimation of the?-emission cross sections,we modify the Gilbert-Cameron level density formula in the statistical model by introduce an additional correction term of?clusters.As a result,the modified statistical model well reproduce the experimental data of the?-emission cross sections,thus providing a possible way to resolve the discrepancy of the?emissions.Moreover,the angular dis-tributions of the evaporation residues and the energy spectra of the emitted?particles are also successfully described by our modified statistical model.All these results show that the?clustering effects play an important role in the fusion-evaporation reactions between light-heavy ions,and the modified statistical model is a reliable way for these reaction processes.We also give a comprehensive research between the^16-18O+¹⁶O and^16,18O+^12,13C fusion-evaporation reactions.It is found that the underestimation of the?cross sections widely exists in these two kind of reactions.We develop our previous work by introducing an?-clustering correction term which depends on the mass number of the nucleus.Compared with the previous one,the improved clustering correction term has fewer input parameters.The calculations show that the improved statistical model gives a lot of satisfactory results both for the^16-18O+¹⁶O and the^16,18O+^12,13C reactions.These results prove that?-clustering effects generally exist in the fusion-evaporation reactions between light-heavy ions,and our implementation of this effect in modified statistical model dose capture the physical essence.