Measurements of stopping cross sections of liquid water for fast protons and helium ions

Stopping cross sections of liquid water for MeV energy protons and helium ions have been measured by using a liquid jet target in vacuum. Energy loss spectra after passing through the target were measured at scattering angles from 5.0 to 50 mrad. The energy loss spectra have been successfully reproduced by Monte Carlo simulation calculations (GEANT4 v9.1.p03 toolkit) by taking account of multiple scattering of projectile particles inside the target. For protons, the stopping cross sections were deduced in an energy range from 0.3 to 2.0 MeV. It was found that the present data are in fairy good agreement with recent theoretical calculations.