Both 13C 16O and 22Ne 25Mg reactions perform a cosmic role in the production of neutrons in AGB stars, which significantly contributes to the nucleosynthesis via the s-process. The astrophysical S-factor for both reactions has been calculated in this research, utilizing EMPIRE code and depending on two parameter sets for the optical potential: McFadden and Satchler (MFS), and Avrigeanu and Hodgson (AH) for the non-resonant region of the spectrum, and over a temperature range . The extrapolated S-factor at zero energy is derived to be  and  for 13C 16O,  and  for 22Ne 25Mg from using MFS and AH parameter sets respectively, and they show a reasonable agreement with the most recommended value. The differences in the S-factor, S(E), values obtained from these two adopted parameters set, were attributed to the variations of the real potential term's diffuseness parameter that affecting the reaction cross section, hence S-factor, and specifically at low energy region. Moreover, the present results imply an influential enhancement of the rates by the electron shielding effect at the low-temperature region  in which 13C 16O reaction activated, and especially on 22Ne 25Mg reaction. In addition, for both adopted reactions and overall selected temperature range, the reaction rates using  values based on MFS showed acceptable results with other previous compilations and reference libraries. While that obtained from AH exceed all other compilations even though the resonance contributions are currently unconsidered.

There are many neutron sources in the universe that play an important role in the stellar slow neutron capture (s-process) nucleosynthesis. Fluorine-19 is a cosmically rare isotope that is generated in a series of reactions. The aim in this paper is to perform theoretical calculations to test the variance of neutron intensity generated within stellar conditions, especially in Asymptotic Giant Branch (AGB) stars, on the production of 19F isotope. EMPIRE II program has been utilized with the aid of many Matlab programs, and experimental comparisons have been made with NACRE II and Reaclib libraries. The results has shown that the high abundances of reactant nuclei responsible for ultimately generating 19F are consumed by neutron poisoning reactions that highly affect the final generation of 19F isotope. Also, the Seff and S(0) values for the reaction  have been approximately calculated in the present research.

The present paper focuses on the nature of the different interactions between cometary nucleus and tail with solar wind. The dynamics of the comet will impose many features that provide unique behavior of the comet when entering the solar system. These features are reviewed in this paper and few investigations are made. The calculations made in this work represent the analysis and interpretation of the different features of the comet, such as perihelion and eccentricity dependence on the gas production rate, and the dependence of the latter on the composition of the comet nucleus. The dependences of the heliocentric, bow shock, contact surface, and stand-off distances with gas production rate for many types of comets that cover linear and non-linear types are studied in this work. Important results are obtained which indicated the different physical interactions between cometary ions and solar wind. Furthermore, the important relation between mean molecular weight and gas production rate are analyzed and studied in this work and a conclusion is made that, as the gas production rate increases, the mean molecular weight will decrease exponentially. A detailed discussion for this unique relation is given.

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