The Study Of The Nuclear Rainbow Scattering Of Exotic Nuclei

The nuclear rainbow is a refractive phenomenon occurring in the collision process of nuclei,which arises from the weak absorption feature of the colliding system.It mostly happens in the elastic scattering process of light heavy ions at intermediate energies.It manifests itself as the Airy oscillation pattern and the structureless exponential decay?i.e.the nuclear rainbow falloff?.The nuclear rainbow scattering is very meaningful to understand the internal structure of nuclei.It can be used to extract the key nuclear information such as the real strength of the optical potential between the projectile and the target at a small distance,the nuclear-matter density dependence of the nucleon-nucleon interaction and the incompressibility of the cold nuclear matter.For the elastic scattering of stable nuclei,the existence of the nuclear rainbow has been confirmed experimentally.Many theoretical investigations have been performed as well.For the exotic nuclei far away from the line of?stability,some theoretical investigations indicate that the nuclear rainbow can happen as well.But this has not been confirmed experimentally due to the limited number of experiments.And its mechanism has not been understood well.The present thesis investigates the existence and the mechanism of the nuclear rainbow scattering of exotic nuclei experimentally and theoretically.To verify the existence of the nuclear rainbow scattering of exotic nuclei,the?quasi-?elastic scattering of the weakly-bound neutron-rich ¹⁷C and the weakly-bound proton-rich ¹⁷F have been investigated successively.The two nuclei are both loosely bound and have the structure exhibiting the weak absorption.For ¹⁷C in the neutron-rich area,the quasi-elastic scattering experiment of ¹⁷C on ^natC at 40 AMe V has been carried out at the HIRFL-RIBLL1 termination in Institute of Modern Physics?IMP?at Lanzhou and the corresponding angular distribution is obtained.The optical model and coupled channel analyses have been performed successively and the experimental data are reproduced very well.The optical potential parameters are obtained and found similar to those of ¹⁶O+¹²C at a similar energy.Based on the near-/far-side scattering decomposition,it is found that the farside component dominates at large angles and the rainbow falloff appears in the elastic scattering angular distribution.This reflects the strong refraction of the elastic scattering of¹⁷C+¹²C.The ¹⁷C+¹²C system is compared with the colliding systems including the stable carbon isotopes and it is found that their optical potential parameters are similar.This fact indicates that,compared with the elastic scattering of stable carbon isotopes,the one of ¹⁷C does not have an obvious stronger absorption and has the opportunity to experience the nuclear rainbow scattering process.For ¹⁷F in the proton-rich area,the existent elastic scattering data of ¹⁷F+¹²C at 10 AMe V is investigated.Based on the cluster description of¹⁷F=¹⁶O+p,the CDCC calculation is performed to analyze the elastic scattering angular distribution.In the calculations,the unambiguous optical potential of ¹⁶O+¹²C and the global optical potential of p+¹²C are utilized.The calculation reproduces the data points well and predicts two Airy minima at large angles.The Airy pattern is very similar to that of the elastic scattering of ¹⁶O+¹²C.The data is also analyzed with the optical model.The optical potential parameters of ¹⁷F+¹²C are obtained and two Airy minima are observed again.The aforementioned analyses indicate that the elastic scattering of ¹⁷F+¹²C should have the nuclear rainbow phenomenon.To have an insight of the nuclear rainbow scattering of exotic nuclei,the elastic scattering of ¹⁷F,the weakly-bound stable nucleus ⁶Li and the two-neutron halo nucleus ⁶He have been investigated successively.All of the three nuclei are loosely bound and have a tightly bound core.For the elastic scattering of ¹⁷F+¹²C,the role played by the tightly-bound core ¹⁶O in the formation of the nuclear rainbow is studied.Firstly,the effects from the breakup coupling and the proton optical potential on the elastic scattering angular distribution are analyzed.And it is found that their effects are small.Based on this fact,the one-channel?1-ch?calculations are performed for the elastic scattering of ¹⁷F+¹²C at different energies.It is found that the energy dependence of the position of the first Airy minimum is very similar to that of the elastic scattering of ¹⁶O+¹²C.This proves that the tightly-bound core contributes much to the formation of the nuclear rainbow in the elastic scattering of exotic nuclei.For the elastic scattering of ⁶He and ⁶Li,the work consists of two aspects.?1?The coupling effects from the breakup channels on the nuclear rainbow pattern are investigated based on the cluster description of ⁶He and ⁶Li.With the help of the CDCC method,the elastic scattering of ⁶Li on ¹²C,⁴⁰Ca,⁵⁸Ni and ⁹⁰Zr at 35 AMe V and that of ⁶He on ⁵⁸Ni are analyzed.By comparing the CDCC calculation results with those of 1-ch calculations and performing the near-/far-side scattering decomposition,it is found that the breakup coupling not only causes more abroption,but promotes the development of the nuclear rainbow feature to larger angles because more attraction is introduced due to the breakup coupling,which can strengthen the refractive effects.?2?The abnormal weak absorption of the elastic scattering of ⁶He+¹²C at intermediate energies is investigated.To explain the appearance of this phenomenon,the energy dependence of the?+¹²C optical potential is considered in the CDCC calculation,and the 3?cluster structure of ¹²C is included in the optical model calculation based on the double folding cluster model.However,it is found that the abnormal weak absorption is not caused by the two factors.Besides,in the above calculations of ⁶He at intermediate energies,the strong refractive feature is observed in the both cases.Apart from the direct investigations of the existence and the mechanism of the nuclear rainbow scattering of exotic nuclei,their absorption feature is analyzed from the viewpoint of the total reaction cross sections.Based on the strong absorption model and the Rho N model,a semi-microscopic total reaction cross section model called Rho NX has been developed.In this model,the Fermi motion effect of the nucleons in a nucleus is included and the nuclear density distribution systematics of the S?o Paulo potential is adopted.With this model applied to the colliding systems including ¹²C,the parameter-free total reaction cross section formula is obtained.It is suitable for the energy in the range of 30?1000 AMe V and the mass number in the range of 6?100.This model is applied to ¹⁷C,⁶Li and ⁶He.By comparing the results with those of the direct nuclear reaction calculations,it is found again that the absorption accompanying the scattering of ¹⁷C is not significantly strong and that of ⁶He is abnormally weak.The present thesis points out the existence of the nuclear rainbow phenomenon in the elastic scattering of exotic nuclei,deepens the understanding of the effects of the tightly-bound core and the breakup coupling on the nuclear rainbow scattering,and excludes two possible factors of the abnormal weak absorption of the scattering of ⁶He+¹²C.Meanwhile,a parameter-free?+¹²C optical potential is provided,a full-cluster description of the elastic scattering of the halo nucleus ⁶He on ¹²C is realized,and a semi-microscopic model of the total reaction cross section is given.