Energy andZ2dependences of energy straggling for fast proton beams passing through solids

The energy and $Z_2$ (target atomic number) dependences of energy straggling for fast proton beams are investigated using nuclear resonance reactions of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$(p,αγ${)\mathrm{}}^{16}$O and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$(p,γ${)\mathrm{}}^{28}$Si. The results are compared with theoretical predictions based on the free-electron models (of Bohr and of Vavilov) and the local-electron-density models (of Lindhard and Scharff and of Chu). Concerning both energy and $Z_2$ dependences, the experimental data agree well with Chu’s prediction using the Hartree-Fock-Slater charge distributions of the target atoms.