Bragg-Rule Applicability to Stopping Cross Sections of Gases forαParticles of Energy 0.3-2.0 MeV

The additivity of atomic stopping cross sections, Bragg's rule, is tested for $\alpha$ particles in the gaseous compounds ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, ${\mathrm{O}}_2$, N${\mathrm{H}}_3$, ${\mathrm{N}}_2$O, CO, C${\mathrm{O}}_2$, C${\mathrm{H}}_4$, ${\mathrm{C}}_2$ ${\mathrm{H}}_2$, ${\mathrm{C}}_2$ ${\mathrm{H}}_4$, ${\mathrm{C}}_2$ ${\mathrm{H}}_6$, ${\mathrm{C}}_3$ ${\mathrm{H}}_6$ (propylene), and ${\left(\mathrm{C}{\mathrm{H}}_2\right)}_3$ (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.