Isotope Effect as a Function of Alpha-Particle Energy in the Ionization of Hydrocarbon Gases

In this work the isotope ratio, i.e., the ratio of the ionization produced by a given alpha particle in a deuterated hydrocarbon gas to the corresponding ionization in an undeuterated hydrocarbon gas, was investigated as a function of alpha-particle energies in the range 5.8–1.6 MeV. Alpha particles from 244Cm, 210Po, and 147Sm were employed. Particles reduced energies were also obtained by passing alpha particles through thin mica windows. The isotope effect was larger in the hydrocarbons investigated than for our previous experiments for ionization by beta particles from 63Ni. For the hydrocarbons methane, ethane, acetylene, and ethylene there was found to be a very small increase of the order of 1%–3% in the isotope ratio as one decreased the alpha-particle energy from 5 to 1.6 MeV. A tentative explanation of this change with alpha energy has been advanced.