EBS and in-beam $\gamma$-ray investigation of FCVA-prepared Cr${}_2$O${}_3$ targets for low-energy ${}^{16}$O+${}^{16}$O fusion experiments

Abstract

The Cr${}_2$O${}_3$ solid target for low-energy ${}^{16}$O+${}^{16}$O fusion experiments was fabricated using filtered cathodic vacuum arc (FCVA) deposition. Its composition, oxygen areal density and impurity content were characterized by elastic backscattering spectrometry (EBS), and the impurity-induced background contributions were investigated by in-beam $\gamma$-ray spectroscopy. EBS results indicate that the Cr${}_2$O${}_3$ film exhibits good stoichiometry and uniformity, with ${}^{16}$O areal densities ranging from $(3.24-3.25)\times 10^{17}$ atoms/cm${}^2$. The EBS analysis reveals a carbon atomic fraction of approximately 1.25-1.29\% in the Cr${}_2$O${}_3$ layer, while a large amount of carbon impurities are also identified on the surface of Cr substrate. In-beam $\gamma$-ray spectra reveal prominent transitions associated with ${}^{27}$Al and ${}^{24}$Mg at 844, 1015, and 1369 keV, mainly originating from ${}^{12}$C+${}^{16}$O fusion reactions induced by carbon impurities under ${}^{16}$O irradiation. Meanwhile, characteristic $\gamma$-rays emissions from evaporation channels of the ${}^{16}$O+${}^{16}$O reaction, including ${}^{31}$S, ${}^{31}$P, and ${}^{28}$Si, were also observed and can be used to extract the ${}^{16}$O+${}^{16}$O fusion cross sections. This work provides an experimental basis for the development of high-purity oxide targets and the optimization of target configurations for future low-background ${}^{16}$O+${}^{16}$O fusion cross section measurements.