| In this dissertation, the theory of radiative capture reaction and the s-process of nucleosynthesis of heavy element of astrophysics have been investigated.To research the radiative capture reaction, we study systematically Asymptotic Normalization Coefficient method (It is called 'ANC' method for short). We give a mathematical proof for the model-approximately independence of ANC coefficient. Combining a concrete nuclear reaction, we check up the model-approximately independence of ANC coefficient with numeric calculation. Under the El transition condition, a expressions with ANC coefficient to compute the cross section of radiative capture reaction has been given in this thesis.Using the theory of radiative capture reaction and combining our department experiment, we investigate two nuclear reactions, 11C(p, y)12N and 12C(n, y)13C, and calculate the cross sections and astrophysical reaction rate of them.For the 11C(p, y)12N reaction, we calculate the direct capture reaction, two resonance state (2+ and 2-) capture , the interference between direct capture and 2-resonance state and the total cross sections and astrophysical nuclear reaction rates. The results show that the contribution of direct capture is primary in the interested temperature range of astrophysics. Toward the 12C(n, y)13C reaction, our calculations are good agreement with a recent experiment at low energy. A obvious enhancement of the cross section of 12C(n, y)13C first excited state has been found, and it supports that the first excited state 1/2+ of 13C is a neutron halo state which has been found experimentally by our department group. It is the first time to find the halo state in excited state internationally. Simultaneously, enhancement of the cross section must has had been played an important role in astrophysical nuclear process.We investigate the s-process of nucleosynthesis of heavy element of astrophysics and give a group of analytic solutions for the s-process. To check up the analytic solutions, we calculate the N distributing of the heavy element of s-process in Solar System and the result is good agreement with astronomic measurement. Moreover, we compute the change against neutron irradiation of heavy element abundance in typicalbranching point 85Kr of s-process and result is good agreement with the former too.One of the important problems of nucleosynthesis of heavy element is the neutron source. A steady neutron source is necessary of nucleosynthesis of heavy element. Commonly, the reaction 13C( ,n)16O is considered as the main neutron source in s-process, so the most important input nuclear data must be the nuclear reaction rate of 13C(a,n)16O.Basing on the up to date experimental results, the S-factor is more less than the one which had been used in the current investigation of neutron source of s-process. With the new data, we calculate the astrophysical nuclear reaction rate of 13C(a,n)16O and the result show it is only 1/2.37 of current under the typical astrophysical environment of 13C(a,n)16O neutron source. This will bring biggish impact of s-process neutron source and challenge the model of star evolution.At the same time, we think that the nuclear reaction 12C(n, y)13C has influence for neutron source of s-process because it capture neutron turning into neutron poison , on the other hand produce 13C becoming seed of neutron source.In this dissertation, a analytic solution of neutron source of s-process in AGB star has been given. With the up to date experimental data of 13C( ,n)16O and 12C(n,y)13C reaction rate, we carry out a analytic research for neutron source of s-process. Our results show that with the up to date experimental data, 13C can not sufficiently burn, the neutron number density decrease, the timescale of neutron source become long and these come into conflict with model of Thermal Pulse AGB star. Via theoretic analysis, we think that both of the increase in typical temperature of AGB star model and the corresponding change of model are possible ways to solve conflict.
|
PDF Full Text Request