Underground nuclear astrophysics in Europe: a status update

The cross sections of nuclear reactions taking place in stars and in the Big Bang are generally so low that they can only be measured in the low-background environment of an underground accelerator. The talk will report about progress achieved in the past year at the world’s only such machine, the LUNA 0.4 MV accelerator in Gran Sasso/Italy. The 2H(α,γ)6Li cross section has been measured for the first time directly in the Big Bang energy region, pinning down the amount of primor- dial 6Li. Measurements of the 17O(p,α)14N and 22Ne(p,γ)23Na cross sections important for nucleosynthesis in an astrophysical nova are underway at LUNA, and preliminary data at unprecedented low en- ergies are already available. An activation study of the 40Ca(α,γ)44Ti reaction using offline counting in the Felsenkeller underground labora- tory in Dresden has yielded new and more precise resonance strengths. In order to apply the method of underground nuclear astrophysics to topics such as helium and carbon burning and the neutron sources for the astrophysical s-process, it is necessary to install a higher-energy accelerator underground. The status of the relevant new accelerator projects at Gran Sasso and at Felsenkeller will be reported.