Track formation inSiO2quartz and the thermal-spike mechanism

α-quartz has been irradiated with heavy ions: ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, and ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ at an energy of about 1 MeV/amu in order to cover a range of electronic stopping powers dE/dx between 2.4 and 9 keV/nm and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$, ${}_{}{}^{128}{}_{}{}^{}\mathrm{Te}$, ${}_{}{}^{129}{}_{}{}^{}\mathrm{Xe}$, ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ between 1 and 5.8 MeV/amu for dE/dx>7 keV/nm. The extent of the induced damage is determined using Rutherford backscattering ion channeling with a 2-MeV ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ beam. The damage cross section A is obtained using a Poisson law ${\mathit{F}}_{\mathit{d}}$=1-exp(-Aφt), where φ is the flux and t the irradiation time. This damage cross section is linked to the effective radius ${\mathit{R}}_{\mathit{e}}$ through the relation A=π${\mathit{R}}_{\mathit{e}}^2$, where ${\mathit{R}}_{\mathit{e}}$ is the radius of an equivalent cylinder of damage. Using high-resolution electron microscopy, cylinders of amorphous matter have been observed, whose radius corresponds to ${\mathit{R}}_{\mathit{e}}$ when the track is continuous (i.e., for A≥1.3×${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^2$; ${\mathit{R}}_{\mathit{e}}$≥2 nm). A thermal-spike model is applied to calculate the radii of the observed tracks assuming that the observed amorphous cylinders correspond to a rapid quench of a molten liquid phase along the ion path. The model is applied only when the latent track is continuous and cylindrical. A good agreement is obtained taking into account that the initial spatial energy deposition on the electrons depends on the ion velocity.