A precise, non-destructive method for determining the areal density of thin graphenic carbon (GC) foils via alpha-particle energy loss is presented. Two types of GC foils — sourced from KETEK GmbH and Applied Nanotech Inc. — were investigated using a three-isotope mixed alpha source emitting particles in the 5.0–5.8 \(\textrm{MeV}\) range. Both foils have similar nominal areal densities of approximately \(0.2\,\mathrm {mg\,cm^{-2}}\) , but differ slightly in chemical composition and microstructure. High-resolution alpha spectroscopy yielded energy-loss measurements with relative uncertainties below 1%. The uncertainty of the extracted areal densities and stopping powers is dominated by the determination of foil mass, area and composition metrology, rather than by the alpha-energy-loss measurement itself. Experimental stopping powers were obtained by combining the measured energy loss with independently determined foil masses and areas, and were compared with established stopping-power models. A modified Bethe formalism incorporating Barkas and Bloch corrections, together with an empirically adjusted mean excitation energy \(I_\textrm{adj}\) , provided the most consistent description of the data across the investigated energy range. The resulting values were \((73 \pm 2)\,\textrm{eV}\) for the KETEK foil and \((85 \pm 3)\,\textrm{eV}\) for the Applied Nanotech foil. The fitted stopping-power curves indicate a systematic difference between the two GC foils, consistent with their differing compositions and microstructures. Because the stopping-power model is calibrated against the same reference foils, however, this interpretation is model-dependent and requires further validation using independently characterised samples. While the method is well suited to thin foils, angular straggling and the non-linear energy dependence of the stopping power may limit its applicability beyond the thin-target approximation. The reported stopping-power data are relevant for benchmarking Monte Carlo simulations and modelling energy deposition in carbon-based materials, with applications in accelerator technology and radiopharmaceutical research. In medical physics, stopping power is closely related to linear energy transfer, which governs the biological effectiveness of alpha-emitting isotopes in targeted therapies.
