Effects of the projectile electronic structure on Bethe–Bloch stopping parameters for Ag

Energy losses of protons and alpha particles in silver have been accurately measured under the same experimental conditions over the velocity range Elab=(0.192–2.595)Elab=(0.192–2.595) MeV/amu using the transmission method. Deduced S(E)S(E) stopping powers are compared to most accurate ones from the literature, to values generated by the SRIM-2008 computer code and to ICRU-49 compilation. They were analyzed in the framework of modified Bethe–Bloch theory for extracting Ag target mean excitation and ionization potential, I, and Barkas effect parameter, b  . Values of (466±5466±5) eV and 1.20±0.011.20±0.01 for these two parameters were inferred from the proton S(E)S(E) data while the alpha particle data yielded values of (438±4)(438±4) eV and 1.38±0.011.38±0.01, respectively. The (I, b) stopping parameters thus exhibit opposite variations as the projectile charge increases, similarly as we have found previously for nickel [6]. This can be ascribed only to an effect of the projectile electronic structure at low velocities. The obtained results are discussed in comparison to previous ones reported in the literature.