The challenging first direct measurement of the 65 keV resonance strength in the ${}^{17}$O(p,$\gamma$)${}^{18}$F reaction at LUNA

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 (from 20 MK to 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 = 16(3) peV. 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 4πBGO detector efficiency was optimized installing an aluminum target chamber and holder. With about 400 C accumulated on Ta2O5 targets, highly enriched in 17O, the LUNA collaboration has performed the first ever direct measurement of the 64.5 keV resonance strength.

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• First direct measurement of the 64.5 keV resonance strength in ${}^{17}$O(p,$\gamma$)${}^{18}$F reaction