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Among the reactions involved in the production and destruction of deuterium during Big Bang Nucleosynthesis, the deuterium-burning D(p,γ) 3 He reaction has the largest uncertainty and limits the precision of theoretical estimates of primordial deuterium abundance. Here we report the results of a careful commissioning of the experimental setup used to measure the cross-section of the D(p,γ) 3 He reaction at the Laboratory for Underground Nuclear Astrophysics of the Gran Sasso Laboratory (Italy). The commissioning was aimed at minimising all sources of systematic uncertainty in the measured cross sections. The overall systematic error achieved (< 3%) will enable improved predictions of BBN deuterium abundance.

Background: The competing 22 Ne(α, γ) 26 Mg and 22 Ne(α, n) 25 Mg reactions control the production of neutrons for the weak s-process in massive and AGB stars. In both systems, the ratio between the corresponding reaction rates strongly impacts the total neutron budget and strongly influences the final nucleosynthesis.Purpose: The 22 Ne(α, γ) 26 Mg and 22 Ne(α, n) 25 Mg reaction rates must be re-evaluated by using newly available information on 26 Mg given by various recent experimental studies. Evaluations of the reaction rates following the collection of new nuclear data presently show differences of up to a factor of 500 resulting in considerable uncertainty in the resulting nucleosynthesis. Methods:The new nuclear data are evaluated and, where possible, correspondence between states observed in different experiments are made. With updated spin and parity assignments, the levels which can contribute to the reaction rates are identified. The reaction rates are computed using a Monte-Carlo method which has been used for previous evaluations of the reaction rates in order to focus solely on the changes due to modified nuclear data.Results: The evaluated 22 Ne(α, γ) 26 Mg reaction rate remains substantially similar to that of Longland et al. but, including recent results from Texas A&M, the 22 Ne(α, n) 25 Mg reaction rate is lower at a range of astrophysically important temperatures. Stellar models computed with NEWTON and MESA predict decreased production of the weak branch s-process due to the decreased efficiency of 22 Ne as a neutron source. Using the new reaction rates in the MESA model results in 96 Zr/ 94 Zr and 135 Ba/ 136 Ba ratios in much better agreement with the measured ratios from presolar SiC grains. Conclusion:The 22 Ne+α reaction rates 22 Ne(α, γ) 26 Mg and 22 Ne(α.n) 25 Mg have been recalculated based on more recent nuclear data. The 22 Ne(α, γ) 26 Mg reaction rate remains substantially unchanged since the previous evaluation but the 22 Ne(α.n) 25 Mg reaction rate is substantially decreased due to updated nuclear data. This results in significant changes to the nucleosynthesis in the weak branch of the s-process.