6.0–10.0−MeV∕uHe2+-ion-induced electron emission from water vapor

Abstract

We discuss absolute doubly differential cross sections (DDCS's) for the energy and angular distributions (20\ifmmode^\circ\else\textdegree\fi{}--160\ifmmode^\circ\else\textdegree\fi{}) of secondary electrons produced in the collisions of 6.0- and $10.0\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{He}}^{2+}$ ions with water vapor. Details of our experiments were reported in our previous paper [D. Ohsawa et al., Nucl. Instrum. Methods Phys. Res. B 227, 431 (2005)], which mainly considered the total uncertainty $(\ifmmode\pm\else\textpm\fi{}13%)$, as well as absolute DDCS data $(7--10\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ by $6.0\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{He}}^{2+}$ ions. All DDCS data, including the newly obtained data $(20--12\phantom{\rule{0.2em}{0ex}}000\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ by $10.0\text{\ensuremath{-}}\mathrm{MeV}∕\mathrm{u}$ ${\mathrm{He}}^{2+}$ ions, are compared with classical theories after being corrected for relativistic effects. Based on the Rudd model and the Rutherford cross section, the experimental results are discussed by taking account of the momentum spread of the bound electrons. This paper mainly describes the analysis of low-energy electrons and binary encounter peaks at high energies, as well as details of relativistic corrections.