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

Abstract

A precise determination of proton capture rates on oxygen is mandatory to predict the abundance ratios of the oxygen isotopes in a stellar environment where hydrogen burning is active. The 17O(p,γ)18F reaction, specifically, plays a crucial role in AGB nucleosynthesis as well as in explosive hydrogen burning occurring in type Ia novae. At temperatures of interest for the former scenario (20 MK ≤ T ≤ 80 MK) the main contribution to the astrophysical reaction rate comes from the Ec.m. = 65 keV resonance. The strength of this resonance is presently determined only through indirect measurements, with an adopted value of ωγ = (1.6 ± 0.3) × 10−11 eV. Thanks to the low background environment of the Laboratori Nazionali del Gran Sasso, the intense and stable beam provided by the LUNA 400 kV accelerator and the experience in oxygen target production, the LUNA collaboration is aiming the first direct measurement of the above mentioned resonance strength. In the present work details of challenging direct measurement planned at LUNA will be described.

Impact of Neutron Sources of Stellar Reactions on Fluorine Abundances

“…It is better if one could separate the effects of each stage on the final product of 19 F, starting with the most effective sources. reaction is depending on the neutron source from alpha particle reaction with 13 C. Thus, this work will focus on determining the general conditions that impact the strongest of the neutron source reactions especially in AGB stars, namely C 13 (𝛼, 𝑛) O 16 , on 19 F abundances. To do this, we first theoretically calculate the neutron yield from C 13 (𝛼, 𝑛) O 16 , then the sensitivity of this on the proton yield of N 14 (𝑛, 𝑝) C…”

“…This could give a rough estimate of the effects that stellar neutron sources on 19 F final production, Figure (1). Then, reaction rates will be calculated for both C 13 (𝛼, 𝑛) O 16 , and N 14 (𝑛, 𝑝) C 14 for the temperature range ~ 10 GK. Few programs have been written to perform the present calculations using the MATLAB program, and cross-section values have been calculated from EMPIRE program.…”

“…When considering neutron nuclear reactions near stellar cores or in other extreme density sites, the reaction rates of Eq. ( 4) should be reconsidered by taking into account the Maxwellian Averaged Cross-section 𝜎 𝑀𝐴𝐶𝑆 [6], thus, 𝑁 𝐴 〈𝜎𝑣〉 = 𝑁 𝐴 𝜎 𝑀𝐴𝐶𝑆 𝑣 𝑇 × 10 −24 cm 3 mol −1 sec −1 (10) Where v T is the average velocity at T. There are few experimental techniques to calculate 𝜎 𝑀𝐴𝐶𝑆 [8,16].…”

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

“…Since the expected rate is as low as one reaction per Coulomb [8], a direct measurement of the E R = 65 keV resonance strength required both a high sensitivity setup and a devoted technique for beam-induced background (BIB) suppression. In following sections the setup, the analysis and the preliminary results found will be described.…”