A facility for direct measurements for nuclear astrophysics at IFIN-HH - a 3 MV tandem accelerator and an ultra-low background laboratory

We present a facility for direct measurements at low and very low energies typical for nuclear astrophysics. The facility consists of a small and robust tandem accelerator where irradiations are made and an ultra-low background laboratory located in a salt mine where very low radio-activities can be measured. Both belong to Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), but are situated 120 km apart. Their performances are shown using a few cases where they were used. We argue that this facility is competitive for the study of nuclear reactions induced by alpha particles and by light ions at energies close to or down into the Gamow windows. A good case study was the C-13+C-12 fusion reaction, where the proton evaporation channel leads to an activity with T-1/2=15 h, appropriate for samples' transfer to the salt mine. Measurements were done using the thick target method down into the Gamow window for energies from E-c,E-m = 2.2 MeV, which is the lowest energy ever reached for this reaction, up to 5.3 MeV, using C-13 beams from the 3 MV Tandetron. The activation method allowed us to determine a cross section of the order of 100 pb. Reactions induced by alphas were also measured. Proton induced resonant reactions were used to calibrate the accelerator terminal voltage. Some results of the experiments characterizing the assembly are shown and discussed.