Ionization of methane and ethane by x rays: Effect of fluid density on energy absorption (dosimetry)

Abstract

When a fluid contained in a glass or steel cell is irradiated with x rays, the energy absorbed by the fluid is not a linear function of the fluid density over the range 1–1000 kg/m3. A semiempirical model is presented to estimate the absorbed energy as a function of density. The model is based on the energy distribution and ranges of secondary electrons at different densities. The dose measured in air at 1 atm pressure and 298 K is used as a reference. The model is tested against data on the ionization of air at densities 1–5 kg/m3, methane at 12–453 kg/m3, and ethane at 28–571 kg/m3. The yields of ionization estimated with the model increase at high densities, in agreement with an earlier theory of ionization in dense fluids.