Abstract Details

Name: Dr. Rulee Baruah
Affiliation: HRH The Prince of Wales Instt. of Engineering and Technology
Conference ID: ASI2017_764
Title : Electron capture and beta decay rates in highly explosive scenario of type II supernova
Authors and Co-Authors : Dr. Kalpana Duorah, Gauhati University, Guwahati
Abstract Type : Poster
Abstract Category : Extragalactic astronomy
Abstract : The r-process (rapid neutron capture process) nucleosynthesis in traditionally considered to be responsible for synthesis of most of the heavy elements beyond iron. Though the site of the r-process is still not clearly known, it has been proposed that explosive and dynamic astrophysical environment of core collapse type II supernova is a viable site. Various weak interaction processes, chiefly electron capture and beta decay play a crucial role during the late stage of stellar burning and subsequent gravitational collapse for a supernova type II. After collapse the bounce pushes the material outward in form of shock wave where the energy of neutrinos eventually causes the explosion. The outward propagation of the shock depends on the rates of these processes. For most of the heavy and superheavy elements produced here, the experimental information is largely scarce. So a theoretical approach is considered a first step for gathering information on the nuclei produced in such environments. Astrophysical parameters needed for our analysis are temperature (> 109 degrees K) and neutron number density which we take to be greater than 1020 cm-3. In the later expansion stages after SN explosion where the neutron density supposedly falls, the r-process nucleosynthesis produces the heavy elements which subsequently beta decays and the r-process path forms. Along the path , the experimental data of observed elements matches our calculated ones. Later ejecta are neutron-rich (Ye < 0.5) and leaves behind a compact neutron star or a black hole depending upon the initial contracting mass. We note that the element 98Cf 254 shown by the SN light curves is found in our classical astrophysical condition of T = 1.9× 109 K and nn = 1020 cm-3. Also we note an element of mass 273 corresponding to atomic number 115, at temperature 3.0 × 109 K and neutron density 1020 cm−3. The decay rates of these elements are found to be very much higher than their electron capture rates. The electron capture precedes beta decay during collapsing stage of a massive star. But just after explosion as temperature and density decrease exponentially and r-process nucleosynthesis starts, the beta decay of the nuclei produced increases Ye, the electron fraction and compete with electron capture.