Gas-Phase Dosimetry by Use of Ionization Measurements

Abstract

A basis is provided for the use of ionization measurements to evaluate energy absorption in gas‐phase dosimetry when high‐energy electrons are employed as the radiation source. It is concluded that total energy absorption can be determined and that stopping powers can be employed to calculate relative energy absorption in various gases. Scattering measurements indicate that irradiation cells should be short. Relative values of the energy required to form one ion pair (W) by 1‐MeV electrons are shown to be the same as those reported for lower energy electrons, and the following W values for the partial absorption of 1‐MeV electrons are reported with a probable error of about ±2%: C₃H₈ 23.4, n‐C₄H₁₀ 22.9, i‐C₄H₁₀ 23.0, i‐C₅H₁₂ 23.9, C₃H₆ 24.8, 1‐C₄H₈ 24.4, trans‐2‐C₄H₈ 23.9, i‐C₄H₈ 24.4, CH₃CHO 26.4, (C₂H₅)₂O 23.8, CO 32.2, SO₂ 30.4, NO 27.5, N₂O 32.9, and NH₃ 26.5. Chemical‐yield measurements on ethylene suggest that the formation of acetylene can be measured with an accuracy of better than ±3%; above 400 Torr and with dose rates in the order of 10¹⁵ eV cc^—1·sec^—1 G(acetylene) = 3.07±0.08.