Stopping cross-sections of various gases for alpha particles in the energy region 0.2 to 5.5 MeV

A single experimental apparatus has been designed to allow measurements of stopping cross-sections of materials in liquid and vapour phase, for alpha particles, using an indirect method. The method, in which residual energies for increasing absorber thicknesses are obtained and differentiated has been used in a number of investigations of phase effects in stopping power. As a set of preliminary experiments, the stopping cross-sections of He, N2, Ar, CH4 and air for 241Am alpha particles have been measured, to allow overall assessment of measurement and data analysis procedures by comparison with other published results. Such comparison suggests that the absolute uncertainty of the techniques employed is unlikely to exceed 4 or 5%. Some of the problems associated with indirect measurements of stopping power are discussed. (author)