Comparative study of electron energy deposition and yields in water in the liquid and vapor phases

Dual sets of Monte Carlo computations were made for electrons in water to assess differences due to the state of condensation. The GSF computer code was used for the vapor and the ORNL code for the liquid. The underlying physical differences specifically incorporated into the liquid code are discussed. At electron energies greater than or equal to 50 eV, ionization is considerably more efficient in the liquid than in the vapor, the high-energy W values for the two phases being 24.6 and 30.0 eV/ip. Above 50 eV, the Fano factor is about half as large in the liquid as in the vapor. The single-collision spectrum in the liquid is harder, giving a greater stopping power in the range 50 to 104 eV, beyond which the liquid and vapor stopping powers merge. Slowing down spectra for 103- and 104-eV electrons and depth-dose curves for 1-keV electrons are calculated. In addition, the radial dose distributions around electron paths in liquid and vapor are compared