The range-energy relation for α-recoil atoms

Abstract

The ranges of ThC" α-recoil atoms have been redetermined at pressures of hydrogen, argon, and air from 10-3 to 30 mm, by collection on a silver plate mounted 3 mm from a platinum source plate. The collector was maintained at a positive potential of 300 V to prevent collection of ions which migrate by diffusion. A similar method is used for RaA, with a (gaseous) radon source. Previous work is critically discussed in terms of the corrections necessary to allow for (i) geometrical features, and (ii) range straggling. Values of the mean range calculated both from previous work and from the present work are plotted against the recoil energy. Both the Fl�gge-Zimens recoil-range equation and the stopping power equation are shown to be unsatisfactory, and to rest on arguments which are subject to serious objection on both experimental and theoretical grounds. The recent Bohr treatment of collisions between recoil atoms and gaseous atoms is In much better agreement with the unobjectionable experimental data available.