Isotopic neon cross sections for a study of neutron balance and temperature during s-process nucleosynthesis

Abstract

The neutron source of the s-process is believed to be the <SUP>22</SUP>Ne(α, n) reaction, taking place in the He-burning shell of a pulsating red giant. Such a periodic neutron irradiation leads to an exponential distribution of neutron fluences for the seed nuclei, which can be deduced from the observed solar system abundances. Using this empirically determined distribution of neutron fluences and the abundances and the experimental cross sections of the elements present in the He shell, the number of neutrons captured by each nuclear species during the s-process has been calculated. The authors have measured the capture cross sections of the three stable neon isotopes in the energy range 5-400 keV; the total cross sections were also measured, between 5 and 800 keV. It is concluded that the traditional s-process treatment of the neutron balance yields strong evidence in favor of the <SUP>22</SUP>Ne(α,n) reaction as the effective neutron source to build most s-process abundances.