Energy loss and dissociation of 10-MeV/amu H3+ ions in carbon foils.

Abstract

Energy losses and fractions of ${\mathrm{H}}_{3}^{+}$ and ${\mathrm{H}}_{2}^{+}$ ions emerging from carbon foils of 1--8.5 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ thickness, after incidence of 9.6-MeV/amu ${\mathrm{H}}_{3}^{+}$ ions, have been measured. From the decrease of the transmitted fraction of ${\mathrm{H}}_{3}^{+}$ ions with increasing foil thickness, the dissociation cross section for 9.6-MeV/amu ${\mathrm{H}}_{3}^{+}$ due to the ${\mathrm{H}}_{3}^{+}$-C collision has been determined to be (2.2\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{2}$. Further, the potential energy of the ${\mathrm{H}}_{2}^{+}$+${\mathrm{H}}^{+}$ system has been derived from the energy spectra of the fragment ${\mathrm{H}}_{2}^{+}$ ions, being 9.45\ifmmode\pm\else\textpm\fi{}0.74 eV, with interproton separations being equal to those known for stable ${\mathrm{H}}_{3}^{+}$ ions. For the stopping power of carbon for 9.6-MeV/amu ${\mathrm{H}}_{3}^{+}$ ions a value of 83.3\ifmmode\pm\else\textpm\fi{}5.5 eV/(\ensuremath{\mu}g/${\mathrm{cm}}^{2}$) has been obtained from the energy-loss data. This result corresponds to an effective charge of 1.45\ifmmode\pm\else\textpm\fi{}0.09 for ${\mathrm{H}}_{3}^{+}$ in carbon. The observed stopping power and the derived effective charge agree well with the values calculated by using the first-order Born approximation.