The astrophysical s-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding s-process nucleosynthesis is the neutron flux generated by the 22 Ne(α, n) 25 Mg reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing 22 Ne(α, γ) 26 Mg reaction, is not well constrained in the important temperature regime from ∼0.2-0.4 GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the 22 Ne( 6 Li, d) 26 Mg reaction in inverse kinematics, detecting the outgoing deuterons and 25,26 Mg recoils in coincidence. We have established a new n/γ decay branching ratio of 1.14(26) for the key E x = 11.32 MeV resonance in 26 Mg, which results in a new (α, n) strength for this resonance of 42(11) µeV when combined with the well-established (α, γ) strength of this resonance. We have also determined new upper limits on the α partial widths of neutron-unbound resonances at E x = 11. 112, 11.163, 11.169, and 11.171 MeV. Monte-Carlo calculations of the stellar 22 Ne(α, n) 25 Mg and 22 Ne(α, γ) 26 Mg rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from ∼0.2-0.4 GK.
Several lifetimes in23 Mg have been determined for the first time using the Doppler-shift attenuation method. A Monte Carlo simulation code has been written to model the γ -ray line shape. An upper limit of τ < 12 fs at the 95% C.L. has been obtained for the astrophysically important 7787 keV state.
The 33 S(p,γ ) 34 Cl reaction is important for constraining predictions of certain isotopic abundances in oxygenneon novae. Models currently predict as much as 150 times the solar abundance of 33 S in oxygen-neon nova ejecta. This overproduction factor may vary by orders of magnitude due to uncertainties in the 33 S(p,γ ) 34 Cl reaction rate at nova peak temperatures. Depending on this rate, 33 S could potentially be used as a diagnostic tool for classifying certain types of presolar grains. Better knowledge of the 33 S(p,γ ) 34 Cl rate would also aid in interpreting nova observations over the S-Ca mass region and contribute to the firm establishment of the maximum endpoint of nova nucleosynthesis. Additionally, the total S elemental abundance which is affected by this reaction has been proposed as a thermometer to study the peak temperatures of novae. Previously, the 33 S(p,γ ) 34 Cl reaction rate had only been studied directly down to resonance energies of 432 keV. However, for nova peak temperatures of 0.2-0.4 GK there are seven known states in 34 Cl both below the 432-keV resonance and within the Gamow window that could play a dominant role. Direct measurements of the resonance strengths of these states were performed using the DRAGON (Detector of Recoils And Gammas of Nuclear reactions) recoil separator at TRIUMF. Additionally two new states within this energy region are reported. Several hydrodynamic simulations have been performed, using all available experimental information for the 33 S(p,γ ) 34 Cl rate, to explore the impact of the remaining uncertainty in this rate on nucleosynthesis in nova explosions. These calculations give a range of ≈20-150 for the expected 33 S overproduction factor, and a range of ≈100-450 for the 32 S/ 33 S ratio expected in ONe novae.
The electricity sector supporting all sectors accounts for 38% of the global annual energy-related greenhouse gas emissions (GHG) of 34Gt CO2eq. With this trajectory, the global mean temperature will rise by 2.7 o C by 2100 (at 50% probability). There is no consensus approach to sustainability analysis of net zero electricity (NZE) scenarios or systems. This study has developed a novel, rigorous, holistic LCA-based methodology for robust NZE roadmap/pathway analyses. It identifies the leading fifteen countries with the highest gross domestic products with over 90% GHG. It compiles Ecoinvent life cycle inventory for NZE systems and country mixes and calculates their life cycle impacts using ReCiPe, Impact 2002+, and Environmental Prices methods. The global mean ranking of non-fossil systems is
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