The challenging first direct measurement of the 65 keV resonance strength in the 17O(p,γ)18F reaction at LUNA

A precise determination of the proton capture rates on oxygen is mandatory to predict the abundance ratios of oxygen isotopes in a stellar environment where the hydrogen burning is active. The 17 O(p, γ ) 18 F reaction, in particular, plays a crucial role in AGB nucleosynthesis as well as in explosive hydrogen burning occurring in novae and type I supernovae. At the temperature of interest for the former scenario (20 MK ≤ T ≤ 80 MK) the main contribution to the astrophysical reaction rate comes from the E r = 64.5 keV resonance. The strength of this resonance is presently determined only through indirect measurements, with an adopted value ωγ = (1.6 ± 0.3) × 10 −11 eV. A new high sensitivity setup has been installed at LUNA, located at Laboratori Nazionali del Gran Sasso. The underground location of LUNA 400kV guarantees a reduction of the cosmic ray background by several orders of magnitude. The residual background was further reduced by a dedicated shielding. On the other hand the 4 π -BGO detector efficiency was optimized installing an aluminum target chamber and holder. With about 400 C accumulated on Ta 2 O 5 targets, with nominal 17 O enrichment of 90%, the LUNA collaboration has performed the first ever direct measurement of the 64.5 keV resonance strength.