The Penetrating Power of β-Decay Recoils of Epithermal Energies in Organic Matter

Abstract

A method for the measurement of the extent of dislocation of the β-decaying nucleus from its equilibrium position is described. An ionized layer formed at the surface of an aqueous solution of an ionic surface-active substance served as a source of β-disintegrating atoms. The primary adsorbed surface-active ions give rise to an electrical double layer within the liquid phase. When the solution contains β-active ions, some will join the electrical double layer near the surface as counter ions. It was found that radioactive β-recoils arising in an adsorbed surface layer are able to leave the surface, collected on a negatively charged plate, and counted. In order to reach the gas phase, the β-recoils have to penetrate the primary organic adsorption layer. When the expanded adsorption layer is gradually compressed, particles of lower energy are stopped, resulting in decreased recoil activity. Extrapolation to zero β-recoil activity gives an approximate value for the mass per unit area of organic material which stops completely atoms of certain initial energy. For particle energies between 2 to 22 eV, a linear dependence is found between the maximum β-recoil energy and the "penetrating power". The corresponding organic stopping layers for this energy region are between 1.0 to about 1.6 × 10−7 g/cm2.