Direct measurement of the astrophysical 75As(n,γ)76As reaction at the CSNS Back-n

We report a high-precision measurement of the 75As(n,γ)76As neutron capture cross sections from 1~eV to 1~MeV, performed at the Back-n facility of the China Spallation Neutron Source using the Time-of-Flight method. In the resolved resonance region, seventeen previously unreported resonances were identified, and discrepancies with evaluated nuclear data libraries, particularly at 493 eV and 2368 eV, were clarified. Resonance parameters for the newly observed structures were extracted with the R-matrix code SAMMY.

Maxwellian-averaged cross sections were calculated based on the averaged cross sections in the unresolved resonance region. And the reaction rates for 75As(n,γ)76As reaction were derived over the astrophysically relevant temperature range of the s-process nucleosynthesis model. The present reaction rates deviate significantly from previous theoretical predictions, and the uncertainties are significantly reduced.