^(19)F+^(208)Pb近垒及垒下准弹反应

Quasi-elastic Scattering of ￣(19)F+￣(208)Pb Systemat Near-and Sub-barrier Energies

用电离室△Ｅ－Ｅ望远镜测量了^（１９）Ｆ＋^（２０８）Ｐｂ体系在８８、９１．９３、９６．９８、１０２ＭｅＶ６个能量点的准弹反应角分布，用ＥＣＩＳ程序拟合弹性散射角分布，得到该体系的光学势参数，观察到明显的“阈异常”现象，对转移反应角分布作了分析，得到了产物为Ｃ、Ｎ、Ｏ的转移反应的激发函数，此外，导出了３个主要转移反应道^（２０８）Ｐｂ^（１９）Ｆ^（１８）Ｏ、^（１５）Ｎ、^（１４）Ｃ）的转移几率和最趋近距离的关系，得到斜率因子ｋ。在单核子转移的情况下，ｋ值与半经典计算基本符合；而对于两核子以上转移的情况，ｋ值小于理论值，存在着“斜率反常”的现象。同时发现ｋ值明显与能量相关，这无法用半经典理论解释。

The quasi-elastic scattering angular distributions of￣(19)F+￣(208) Pb system at energies of 88, 91, 93, 96 and 102 MeV have been measured by means of ionization chamber △E-E telescope. The optical potential parameters of the system were obtained from the fit of the angular distributions of the elastic scattering with ECIS code, and the phenomenon of the ' threshold anomaly' is clearly observed. The angular distributions and the excitation functions of the products C, N and O from transfer reactions were also obtained. The slope factor k were deduced from the relations between the transfer probabilities and the closest distances for three main transfer channels. The k values agree with the semi-classical calculation for the single nucleon transfer reaction, but are smaller than the calculation for the mufti-nucleon transfer reactions, and depend on theincident energies. The 'slope anomaly. and the energy dependence of k can not be explained by the semiclassical theory.