Abstract
We review recent progress in theoretical studies of r-process nucleosynthesis in supernova (SN) explosions. We found suitable physical conditions for a successful r-process and that particle and nuclear reactions on light neutron-rich nuclei as well as heavy nuclei play the significant roles in primary r-process. We also review astronomical observations of the neutron-capture elements detected in extremely metal-deficient halo stars. These stars are presumed to be the second generation, and their chemical composition consists of freshly synthesized heavy elements in the first generation exploding SNe in the Galaxy. We discuss cosmochronology by the use of long-lived radioactive nuclei like 232Th (half life τ1/2 = 14.05 Gyr) and 238U (half life τ1/2 = 4.468 Gyr). We found theoretical reason for the universality of r-process abundance pattern for 56 ≤ Z ≤ 70, but that it is not simply extended to 70 < Z including actinides. We propose that the U/Th cosmochronometer is a roburst cosmic clock although Th/Eu is not reliable.
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