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 17O(p,γ)18F 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 Er = 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 4π-BGO detector efficiency was optimized installing an aluminum target chamber and holder. With about 400 C accumulated on Ta2O5 targets, with nominal 17O enrichment of 90%, the LUNA collaboration has performed the first ever direct measurement of the 64.5 keV resonance strength.
The challenging first direct measurement of the 65 keV resonance strength in the 17O(p,γ)18F reaction at LUNA
D. Piatti
2025
Abstract
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 17O(p,γ)18F 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 Er = 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 4π-BGO detector efficiency was optimized installing an aluminum target chamber and holder. With about 400 C accumulated on Ta2O5 targets, with nominal 17O enrichment of 90%, the LUNA collaboration has performed the first ever direct measurement of the 64.5 keV resonance strength.
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