Principle of Universality of γ-Process Nucleosynthesis in Core-Collapse Supernova Explosions

Using core-collapse supernova explosion models, we investigate the principle of the universality of the γ-process, according to which the s / p abundance ratios produced by individual nucleosynthesis episode are almost constant over a wide range of atomic number. The universality originates from the shift of the γ-process layers, the independence of the s / p abundance ratios of the nuclear reactions, and the weak s -process in presupernovae. Our calculations further suggest an extended universality in which the s / p ratios in the γ-process layers are not only constant but also centered around a specific value of 3. To verify this, we propose an astronomical observation of indium isotopic abundance fractions.