Polonium, electrodeposition

Radiometric methods are unique for their ability to provide directly the surface concentration of the adsorbate. A method for in situ study of electrochemical reactions on solid electrodes was invented by Joliot. ° He used a thin gold foil as an electrode which at the same time served as the window of the radiation counter. Johot determined the kinetics and the effect of tartaric acid on polonium electrodeposition on gold. The method was later further developed and improved (e.g.. Refs. 102,103). 

Cowen et al. [5] showed that polonium can be electrodeposited onto carbon rods directly from acidified seawater, stripped from the rods and auto-plated onto silver counting disks with an overall recovery of tracer of 85 4% for an electrodeposition time of 16 h [ 13]. 

Electrodeposition of polonium directly from acidified seawater onto carbon rods. 

Polonium may be purified by various processes. Such purification methods include precipitation of polonium as sulfide and then decomposing the sulfide at elevated temperatures spontaneous decomposition of polonium onto a nickel or copper surface and electrolysis of nitric acid solutions of polonium-bismuth mixture. In electrolytic purification polonium is electrodeposited onto a platinum, gold, nickel, or carbon electrode. 

Much of the early literature of polonium describes methods for separating it from these mixtures many of these have subsequently been adapted to the separation of milligram amounts of polonium from irradiated bismuth and to its purification. The methods range from a simple chemical separation of the element with a tellurium carrier to its electrodeposition on to a more noble metal or its spontaneous electrochemical replacement on the surface of a less noble metal. 

The electrochemical separation of polonium from irradiated bismuth has not been investigated to any extent it appears, however, that electrodeposition from hydrofluoric acid solution offers a practical means of separation (131). 

The activity of 210Po in aquatic samples has to be calculated on the basis of the electrodeposition time of the polonium on a silver disc using... 

Solutions containing the metal, most commonly in nitric acid, will deposit the metal on a platinnm electrode by electrodeposition. Polonium metal is deposited spontaneously from such solutions on to metals such as silver or nickel. The metal can be sublimed off such support metals at low pressures. Thermal decomposition of polonium sulfide also yields the metal. In much the same way as tellurium, the metal can be obtained from its solutions by the action of reducing agents such as hydrazine, tin(II) ion, titanium(III) ion, and dithionite. Such metal precipitates appear as gray-black powders. Thin foils, silvery in color, have been prepared by vacuum sublimation of the metal. 

Electrodeposition of polonium on silver discs, as well as electrolysis of uranium and plutonium on steel discs... 

The need to prepare very thin sample sources for counting necessitates a lengthy radiochemical separation procedure to remove bulk elements efficiently, as well as alpha emitters that will interfere with the spectra (Table 1). Radiochemical procedures and sample mounting onto a planchet are variable in efficiency and can be affected by sample-related factors. It is therefore imperative to use a yield monitor for the procedure if quantitation is required. After radiochemical separation the solution is prepared for alpha counting using electrodeposition, co-precipitation and filtration as a thin source, direct evaporation, electrospraying, or vacuum sublimation. If the planchet is contaminated with polonium, the planchet is heated to remove the volatile polonium. 

---