Properties of fluorine targets and their application on the astrophysically important 19F( p , α )16O reaction

We report on the production and testing of both evaporated and implanted fluorine targets to investigate their stability to irradiation by protons. We produced four targets by evaporating CaF₂ and LiF powder on Ta backings and three targets by implanting 30 keV ¹⁹F ions into stainless steel backings; a $5\mu$g/cm² Cr protective layer was also evaporated on one of these implanted targets. We assessed each target's stability by monitoring the $\gamma$-ray yields of the ¹⁹F($p,{\alpha }_{\gamma }$)¹⁶O reaction. Our results indicate that the evaporated and implanted targets without Cr layer exhibited 30$\%\sim$75% and 13% deterioration after $\sim$2.5 Coulomb/cm², 220–270 keV proton bombardment, respectively. The implanted target with protecting layer exhibited only about 2.5% deterioration, which can be regarded as stable. As we observed stability in one of the CaF₂ evaporated targets up to 0.25 Coulomb/cm² irradiation, this target was used to investigate the two resonances at $E_p=225$ and 237 keV of the ¹⁹F($p,{\alpha }_{\gamma }$)¹⁶O reaction; the resonance parameters we extracted are consistent with the values found in the literature, giving us confidence in our analysis methods and our understanding of the target fabrication procedures described herein. In conclusion, the implantation technique provides a unique means to produce fluorine targets capable of withstanding high beam intensities, which is one of the necessary technical developments for the JUNA (Jinping Underground Nuclear Astrophysics) project in China.