Measurement of (alpha,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions

Abstract

The $γ$-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called $p$ nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for $γ$-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of $α$-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the $p$ nuclei. With the measurement of the $^{164,166}$Er($α$,n)$^{167,169}$Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the $α$+nucleus optical potential in a mass region where $γ$-process calculations exhibit an underproduction of the $p$ nuclei. Using the same optical potential for the $α$-width which was derived from combined $^{162}$Er($α$,n) and $^{162}$Er($α$,$γ$) measurement makes it plausible that a low-energy modification of the optical $α$+nucleus potential is needed.