Article

# Rapid neutron capture process in supernovae and chemical element formation

Journal of Astrophysics and Astronomy (Impact Factor: 0.71). 01/2005; 30(3):165-175. DOI: 10.1007/s12036-009-0013-x

**ABSTRACT**

The rapid neutron capture process (r-process) is one of the major nucleosynthesis processes responsible for the synthesis

of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier

ones are produced by the r-process. Approximately half of the heavy elements with mass number A > 70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the

r-process in supernovae for the production of heavy elements beyond A = 40 with the newest mass values available. The supernova envelopes at a temperature >109 K and neutron density of 1024 cm−3 are considered to be one of the most potential sites for the r-process. The primary goal of the r-process calculations is

to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature

and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. We have

studied the r-process path corresponding to temperatures ranging from 1.0 × 109 K to 3.0 × 109 K and neutron density ranging from 1020 cm−3 to 1030 cm−3. With temperature and density conditions of 3.0 × 109 K and 1020 cm−3 a nucleus of mass 273 was theoretically found corresponding to atomic number 115. The elements obtained along the r-process

path are compared with the observed data at all the above temperature and density range.

of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier

ones are produced by the r-process. Approximately half of the heavy elements with mass number A > 70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the

r-process in supernovae for the production of heavy elements beyond A = 40 with the newest mass values available. The supernova envelopes at a temperature >109 K and neutron density of 1024 cm−3 are considered to be one of the most potential sites for the r-process. The primary goal of the r-process calculations is

to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature

and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. We have

studied the r-process path corresponding to temperatures ranging from 1.0 × 109 K to 3.0 × 109 K and neutron density ranging from 1020 cm−3 to 1030 cm−3. With temperature and density conditions of 3.0 × 109 K and 1020 cm−3 a nucleus of mass 273 was theoretically found corresponding to atomic number 115. The elements obtained along the r-process

path are compared with the observed data at all the above temperature and density range.

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**ABSTRACT:**The rapid neutron capture process (r-process) is one of the major nucleosynthesis processes responsible for the synthesis of heavy nuclei beyond iron. Isotopes beyond Fe are most exclusively formed in neutron capture processes and more heavier ones are produced by the r-process. Approximately half of the heavy elements with mass number A>70 and all of the actinides in the solar system are believed to have been produced in the r-process. We have studied the r-process in supernovae for production of heavy elements beyond A=40 with the newest mass values available. The supernovae envelopes at a temperature >109 K and neutron density of 1024 cm−3 are considered to be one of the most potential sites for the r-process. We investigate the r-process in a site-independent, classical approach which assumes a chemical equilibrium between neutron captures and photodisintegrations followed by a β-flow equilibrium. We have studied the r-process path corresponding to temperatures ranging from 1.0×109 K to 3.0×109 K and neutron density ranging from 1020 cm−3 to 1030 cm−3. The primary goal of the r-process calculations is to fit the global abundance curve for solar system r-process isotopes by varying time dependent parameters such as temperature and neutron density. This method aims at comparing the calculated abundances of the stable isotopes with observation. The abundances obtained are compared with supernova explosion condition and found in good agreement. The elements obtained along the r-process path are compared with the observed data at all the above temperature and density range. - [Show abstract] [Hide abstract]

**ABSTRACT:**Astrophysical reaction rates, which are mostly derived from theoretical cross sections, are necessary input to nuclear reaction network simulations for studying the origin of $p$ nuclei. Past experiments have found a considerable difference between theoretical and experimental cross sections in some cases, especially for ($\alpha$,$\gamma$) reactions at low energy. Therefore, it is important to experimentally test theoretical cross section predictions at low, astrophysically relevant energies. The aim is to measure reaction cross sections of $^{107}$Ag($\alpha$,$\gamma$)$^{111}$In and $^{107}$Ag($\alpha$,n)$^{110}$In at low energies in order to extend the experimental database for astrophysical reactions involving $\alpha$ particles towards lower mass numbers. Reaction rate predictions are very sensitive to the optical model parameters and this introduces a large uncertainty into theoretical rates involving $\alpha$ particles at low energy. We have also used Hauser-Feshbach statistical model calculations to study the origin of possible discrepancies between prediction and data. An activation technique has been used to measure the reaction cross sections at effective center of mass energies between 7.79 MeV and 12.50 MeV. Isomeric and ground state cross sections of the ($\alpha$,n) reaction were determined separately. The measured cross sections were found to be lower than theoretical predictions for the ($\alpha$,$\gamma$) reaction. Varying the calculated averaged widths in the Hauser-Feshbach model, it became evident that the data for the ($\alpha$,$\gamma$) and ($\alpha$,n) reactions can only be simultaneously reproduced when rescaling the ratio of $\gamma$- to neutron width and using an energy-dependent imaginary part in the optical $\alpha$+$^{107}$Ag potential.......