Bragg-rule applicability to stopping cross sections of gases for α particles of energy 0.3 to 2.0 MeV

The additivity of atomic stopping cross sections, Bragg's rule, is tested for α particles in the gaseous compounds H₂, N₂, O₂, NH₃, N₂O, CO, CO₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆ (propylene), and (CH₂)₃ (cyclopropane). Compounds with single and double bonds are found to obey Bragg's rule. Compounds containing triple-bond structure are found to deviate from Bragg's rule by as much as 12.8%, but an empirical triple-bond correction is made to fit all the data of the present experiment. Evidence is seen for a possible physical-state effect.