A combined experimental and theoretical study of the energy loss of protons in fluorides is presented. The measurements were performed in fresh $\mathrm{Al}{\mathrm{F}}_3$ evaporated in situ on self-supported C foils, extending the low-energy range from 25 down to $0.7\mathrm{keV}$. The transmission method is used in combination with time-of-flight spectrometry. The experimental stopping power increases almost linearly with the mean projectile velocity, showing a velocity threshold at about $0.1\mathrm{a.u.}$ These features are well reproduced by a model based on quantum scattering theory that takes into account the velocity distribution and the excitation of the active $2p$ electrons in the ${\mathrm{F}}^{-}$ anions, and the properties of the electronic bands of the insulators. The model also reproduces the threshold behavior measured previously on LiF.

• Received 18 December 2006

DOI:https://doi.org/10.1103/PhysRevA.76.040901