Quantification of Oxygen and Carbon in Calcium Targets for Reliable Ca$(p,p\alpha )$ Measurements

Reliable extraction of Ca$(p,p\alpha )$ cross sections requires accurate correction for oxygen and carbon impurities in calcium targets. In this work, the relative amounts of these light elements in ${}^{40,42,44,48}$Ca targets are determined using 65-MeV proton elastic scattering, where the Ca/Mylar yield ratios provide a direct measure of the corresponding O and C atomic ratios. These experimentally determined ratios are then applied to the 392-MeV $(p,p\alpha )$ spectra to subtract the O and C contributions in a fully data-driven manner. The method does not rely on assumptions about absolute contamination levels or reaction-model calculations, and enables a consistent and reliable determination of Ca$(p,p\alpha )$ yields across the calcium isotopic chain.