Formation of Elements in Neutron Rich Ejected Matter of Supernovae

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The thermal and chemical properties of neutron rich ejected matter of supernovae are investigated from the high-temperature stage (T〜5×10^<10>K) to the low-temperature stage (T〜3.2×10^9K) under an appropriate assumption for the expansion law. We have taken into account changes of the entropy and of the electron mean molecular weight due to beta process, which are essentially different from previous relevant works. The initial n/p ratio is determined by the chemical equilibrium between neutrons, protons and leptons when the matter is opaque to electron neutrinos, whereas it is given by a steady state condition in the case that the matter is transparent. Considering reactions by nucleon weak interaction, nuclear statistical equilibrium and nuclear beta decays, the initial conditions for the r-process such as the abundances of seed nuclei, the neutron flux and the density of the matter are obtained for various expansion speeds and initial n/p ratios. It is shown that the entropy production and the decrease of mean molecular weight of the electron due to the beta process play an important role, and found that in the cases of slow expansion, neutrons are exhausted due to fast nuclear beta decays before the r-process proceeds, whereas in the cases of fast expansion and/or with the large initial n/p ratios, a sufficient amount of free neutrons are left for r-process. Finally the dynamic r-process is discussed on the basis of our numerical results.
理論物理学刊行会の論文
1973-04-25

Formation of Elements in Neutron Rich Ejected Matter of Supernovae

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