The plot shows the observed abundance of the chemical elements in the solar system, on a relative scale. The lightest elements hydrogen, helium, and lithium have been produced in Big Bang nucleosynthesis in the very first minutes of the universe. Two of them, hydrogen and helium, are the most abundant elements observed.

The third and fourth most abundant elements are carbon and oxygen. They originate in hydrostatic stellar helium burning, and they form the basis for many subsequent processes of nucleosynthesis as outlined in the plot.

The light elements up to iron are mainly produced by nuclear fusion processes, whereas the heavy elements beyond iron are mostly the product of neutron capture processes in stars and stellar explosions.

At Felsenkeller, owing to the low background and high beam intensity, resonances in the ²²Ne(α,γ)²⁶Mg nuclear reaction may be studied by in-beam γ-ray spectroscopy. The corresponding states in the ²⁶Mg nucleus may be studied by nuclear resonance fluorescence using the γELBE bremsstrahlung beam. The ²²Ne(α,γ)²⁶Mg reaction is important as a competitor to a main neutron source for the astrophysical s-process:  ²²Ne(α,n)²⁵Mg.

At nELBE, yet another reaction on neon can be studied, namely ²⁰Ne(n,α)¹⁷O which is the time-inverted partner of the ¹⁷O(α,n)²⁰Ne reaction that restores neutrons consumed by a so-called neutron poison reaction to the stellar scenario.

In brief: Higher ²²Ne(α,γ)²⁶Mg yields measured at Felsenkeller and higher ²⁶Mg γ-widths measured at γELBE would lead to a lower number of neutrons in the star. Higher ²⁰Ne(n,α)¹⁷O yields measured at nELBE, by contrast, lead to a higher number of neutrons in the star. 

The ³He(α,γ)⁷Be reaction is important in two distinct astrophysical scenarios:

• It controls the pp-2 and pp-3 parts of the proton-proton chain of hydrogen burning in the Sun, at a temperature of 0.016 GK (Gamow energy 0.025 MeV).
• It affects lithium production in Big Bang Nucleosynthesis (BBN), because the ⁷Be produced in this reaction decays to ⁷Li with 53 days half-life (Gamow energy 0.2 MeV).

Going from right to left in the plot, the ³He(α,γ)⁷Be  cross section (shown parameterized as the astrophysical S-factor S₃₄) has been measured precisely by several independent groups for E ≥ 0.3 MeV, again precisely by the LUNA collaboration (including HZDR scientists) for E = 0.1-0.2 MeV, and only indirectly for E ≤ 0.1 MeV.

The ¹²C(α,γ)¹⁶O reaction affects the ratio of abundances of the two elements carbon and oxygen. It has been studied many times in the past, but at energies that are much higher than the Gamow peak for the relevant astrophysical scenario. 

Due to two subthreshold resonances, one affecting the electric dipole (E1) and another the electric quadrupole (E2) component of the S-factor, the extrapolation from the energies where data exist to the Gamow peak is fraught with uncertainty.