Reduction of deuterium content in carbon targets for C-12 + C-12 reaction studies of astrophysical interest

The C-12(C-12,p)Na-23 and C-12(C-12, alpha)(20) Ne fusion reactions are among the most important in stellar evolution since they determine the destiny of massive (M similar or equal to 8-10 M-circle dot) stars. However, experimental low-energy investigations of such reactions are significantly hampered by ubiquitous natural hydrogen and deuterium contaminants in the carbon targets. The associated beam-induced background completely masks the reaction products of interest thus preventing cross-section measurements at the relevant energies of astrophysical interest, E-cm < 2 MeV. In this work, we report about an investigation aimed at assessing possible deuterium reductions on both natural graphite and Highly Ordered Pyrolytic Graphite targets as a function of target temperature. Our results indicate that reductions up to about 80% can be attained on both targets in the temperature range investigated, T similar or equal to 200-1200 degrees C. A further reduction by a factor of 2.5 in absolute deuterium content is observed when the scattering chamber is surrounded by a dry nitrogen atmosphere so as to minimise light-particles uptake within the chamber rest gas (and thus on target) through air leaks. The results from this study will inform the choice of optimal experimental conditions and procedures for improved measurements of the C-12 + C-12 reactions cross-sections at the low energies of astrophysical interest.