Isotopic r-process abundances produced by supernova explosions

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 >10 9 K and neutron density of 10 24 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 × 10 9 K to 3.0 × 10 9 K and neutron density ranging from 10 20 cm −3 to 10 30 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 ob-R. Baruah ( ) tained along the r-process path are compared with the observed data at all the above temperature and density range.

Environmental Speciation of Actinides

“…The remaining actinides are only produced in high-energy neutron-rich environments typical of nucleosynthesis, nuclear reactors, and nuclear explosions. Models for nucleosynthesis based on the characteristic energy output of a supernova explosion, nuclear structure, decay energies, and half-lives require that 254 Cm and other actinides were synthesized only via rapid neutron capture (e.g., the r -process) during core collapse supernovae. − Because of the short half-lives associated with neutron-rich nuclei, the majority of the actinides underwent a series of α and β decays and spontaneous fission reactions to form lighter elements with Z < 92. The abundance of fission products and other daughter isotopes measured in meteorites (e.g., 136 Xe from fission of 244 Pu) confirms that actinides were more abundant in the early solar system…”

Competition of Electron Capture and Beta Decay Rates in Explosive Astrophysical Scenario of Type II Supernova

“…It is noted that the value of |M| 2 = 0.03 gives the e − -capture rates of FH much in agreement with that of others, as shown in Table 1. So, we now propose that this |M| 2 = 0.03 value be taken in calculating the e − -capture rates at different temperature and density conditions considered in the present analysis by using equation (15) and then compare them with the β − -decay rates of our calculation [16]. These are shown in Figure 1 for 27 Co isotopes and in Figure 2 for 48 Cd isotopes.…”

“…The β − -decay of the waiting point nuclei regulates the relative abundances for different Z and controls the progress of the r-process flow. This is discussed in detail in an earlier paper by these authors [16].…”