The Range of Alpha-Particles in Water

Abstract

A photographic method is described for measuring the ranges of alpha-particles in liquids whose properties are compatible with emulsion sensitivity utilizing a surface deposit of radiocolloid aggregates as point sources of alpha-radiation. The method has been applied to both water of normal isotopic composition and to heavy water containing 97 percent deuterium oxide. Using polonium radiocolloids as a source of 5.3-Mev alpha-particles ranges of 38.1±0.5 and 38.0±0.5 microns were measured in the respective liquids. By conducting the exposure at temperatures below the freezing point the method is also applicable to certain solid media. The ranges of RaF alpha-particles in normal and heavy ice were found to be 41.6±0.5 and 41.5±0.5 microns. The integral molecular stopping power of water is computed to be 1.56±0.02 for an alpha-particle energy of 5.3 Mev. Similar measurements with radium sulfate radiocolloids indicates a molecular stopping power of 1.56±0.02 for the alpha-particles from RaC′, as compared with a computed value of 1.54±0.02. Larger estimates for this constant may originate from water-air interface effects inherent in experiments with an external detector.