Search

The uptake of 137Cs, 65Zn, 106Ru and 60Co by several types of marine sediment was studied by a simple laboratory technique. The reactions were measured as functions of equilibration time, carrier concentration, sediment concentration and salinity. Large values of the distribution coefficients of these radioisotopes at sediment concentration of 0.05 mg/ml were interpreted as nucleation, respectively aggregation of particulate forms of the radioisotopes by sediment particles. Constant distribution coefficients are found at higher sediment concentrations where nucleation is masked by adsorption onto the sediment particles. 137Cs was found to have an uptake proportional to the illite content of the sediments, probably involving an ion-exchange reaction with potassium. The other radioisotopes showed less specific adsorptions. All radioisotope sediment reactions could be represented by the Freundlich isotherm model. The consequences of the uptake, especially the high particulate proportions of the radioisotopes at low sediments concentrations, were discussed with regard to the supply of trace elements to bottom sediments in the open ocean and the availability of artificially introduced radioactivity to filter feeders and benthic life.

The relationship between grain disorder and sites of formation of surface latent-image specks on tabular silver-bromide emulsion grains has been investigated for small latent-image exposures. The technique was to expose the grains, partially develop them to reveal the sites at which developable latent-image specks had been formed, and then to form photolytic silver in the grains to decorate the disorder. It is shown by an electron-micrographic technique that many of the surface latent-image specks are formed where lines of platelets of photolytic silver meet the grain edges. It is concluded that in grains of the above type there may exist at least one specific type of disorder which provides surface sites where nucleation and aggregation of silver occur preferentially at small exposures. A direct demonstration is presented of the competition between surface and internal sites on and within a grain for the electrons produced by exposure.