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

Abstract

Reliable extraction of Ca$(p,pα)$ 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 $(p,pα)$ 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$(p,pα)$ yields across the calcium isotopic chain.

Figures (4)

• Figure 1: The Grand Raiden spectrometer was positioned at a laboratory angle of $\theta_{\rm lab}=28^\circ$ with respect to the beam axis. Elastically scattered protons were transported to the focal plane and measured using drift chambers for position determination and plastic scintillators for energy-loss and timing measurements. Identical spectrometer settings were employed for the Ca and Mylar targets to ensure identical kinematic and acceptance conditions.
• Figure 2: Grand Raiden focal-plane $X$ position distributions corresponding to the energy spectra of protons from 65-MeV elastic scattering on the Mylar, $^{\rm nat}$Ca, $^{42}$Ca, $^{44}$Ca, and $^{48}$Ca targets.
• Figure 3: $(p,p\alpha)$$S_\alpha$ spectrum for the ${}^{44}$Ca target. The black curve shows the measured spectrum. The blue and green curves indicate the estimated ${}^{16}$O$(p,p\alpha)$ and ${}^{12}$C$(p,p\alpha)$ contributions, respectively, scaled from the Mylar reference data. The red curve represents their sum.
• Figure 4: $(p,p\alpha)$$S_\alpha$ spectrum for the ${}^{40}$Ca target. The black curve shows the measured spectrum. The blue and green curves indicate the estimated ${}^{16}$O$(p,p\alpha)$ and ${}^{12}$C$(p,p\alpha)$ contributions, respectively, scaled from the Mylar reference data. The red curve represents their sum.