Physics
Scientific paper
Jun 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973pthph..49.1932n&link_type=abstract
Progress of Theoretical Physics, Vol. 49, No. 6, pp. 1932-1946
Physics
15
Scientific paper
The effects of electron capture on the changes of temperature and the chemical composition in collapsing dense stars are investigated. Here we have taken into account the entropy production (or less) due to electron captures. This entropy change comes from two factors: One is the entropy loss due to neutrinos emitted by electron capture processes and the other is the entropy change due to the distortion of Fermi distribution of electrons. Results have been obtained by computing numerically under the following assumptions: (1) The density of matter changes with time as if a star contracted without pressure force. (2) Neutrinos emitted by electron capture are assumed to escape freely from a star. Other cooling processes such as energy loss by neutrinos due to (ebar{ν}) (bar{e}ν) interactions and thermal diffusion are neglected. (3) In the higher temperature regions than 3 × 109 °K, nuclear statistical equilibrium is assumed to be attained instantaneously. (4) Beta processes other than electron capture are neglected because of the high degeneracy. As to the beta transition, we have assumed super allowed transition, i.e., (ft)=104 sec for all nuclei. It is found that when the degeneracy parameter ψ is greater than 10, the entropy increases in spite of the energy loss through neutrinos emitted by electron capture. The main chemical elements are found to be limited to the following: n, p, He4, Fe36, Mn56, Cr56, Ca48, Ni78, Zn80, Ge82, Sr120, Ti50, Fe76 and Sr119. The last eight elements are neutron rich nuclei with neutron or proton magic number.
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