The Zr()Zr cross section from the surrogate ratio method and its effect on -process nucleosynthesis

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; Nishio, Katsuhisa   ; Lugaro, M.*; Karakas, A. I.*; Makii, Hiroyuki   ; Mohr, P.*; Su, J.*; Li, Y. J.*; Nishinaka, Ichiro*; Hirose, Kentaro  ; Han, Y. L.*; Orlandi, R.  ; Shen, Y. P.*; Guo, B.*; Zeng, S.*; Lian, G.*; Chen, Y. S.*; Liu, W. P.*

The Zr()Zr reaction cross section is crucial in the modelling of -process nucleosynthesis in asymptotic giant branch stars because it controls the operation of the branching point at the unstable Zr and the subsequent production of Zr. We have carried out the measurement of the Zr(O,O) and Zr(O,O) reactions and obtained the -decay probability ratio of Zr and Zr to determine the Zr()Zr reaction cross sections with the surrogate ratio method. We tested our deduced maxwellian-averaged cross section in stellar models with masses between 2 and 6 and metallicities 0.014 and 0.03. The largest changes - up 80 % variations in Zr - are seen in the models of 3-4 , where the Ne neutron source is mildly activated. The new rate can still provide a match to data from meteoritic stardust silicon carbide grains, provided the maximum mass of the parent stars is below 4 , for a metallicity of 0.03.