Polonium determination

It has been characterized as a bright red solid, which melts in an atmosphere of bromine at about 325 °C. Exposure to the atmosphere converts it to P0O2 and, predictably, it hydrolyzes when dissolved in water. Because of the intense a-radiation emitted by polonium, determination of its crystal structure has been difficult due to the resulting disorder. 

Another area where controlled-potential coulometry has found application is in nuclear chemistry, in which elements such as uranium and polonium can be determined at trace levels. Eor example, microgram quantities of uranium in a medium of H2SO4 can be determined by reducing U(VI) to U(IV) at a mercury working electrode. 

Polonium is unique in being the only element known to crystallize in the simple cubic form (6 nearest neighbours at 335 pm). This a-form distorts at about 36° to a simple rhombohedral modification in which each Po also has 6 nearest neighbours at 335 pm. The precise temperature of the phase change is difficult to determine because of the self-heating of crystalline Po (p. 751) and it appears that both modifications can coexist from about 18° to 54°. Both are silvery-white metallic crystals with substantially higher electrical conductivity than Te. 

Although the Curies noted that one equivalent gram of radium released one hundred calorics of heat per hour, they were uninterested in the practical implications of this, as they were both devoted to pure scientific discovery. During their work with pitchblende in 1898, the Curies discovered two new radioactive elements, which they named polonium (in honor of Marie s homeland) and radium. By 1902 they had isolated a pure radium salt and made the first atomic weight determination. 

In 1898, Marie and Pierre Curie isolated two new radioactive elements, which they named radium and polonium. To obtain a few milligrams of these elements, they started with several tons of pitchblende ore and carried out a long series of tedious separations. Their work was done in a poorly equipped, unheated shed where the temperature reached 6°C (43°F) in winter. Four years later, in 1902, Marie determined the atomic mass of radium to within 0.5%, working with a tiny sample. 

The metal polonium (which was named by Marie Curie after her homeland, Poland) crystallizes in a primitive cubic structure, with an atom at each corner of a cubic unit cell. The atomic radius of polonium is 167 pm. Sketch the unit cell and determine (a) the number of atoms per unit cell (b) the coordination number of an atom of polonium (c) the length of the side of the unit cell. 

Poet, S. E., H. E. Moore and E. A. Martell, Lead-210, Bi-210, and Polonium-210 in the Atmosphere Accurate Ratio and Application to Aerosol Residence Time Determination, J. Geophys. Res.,... 

Various workers [3-7] have discussed the determination of polonium and lead in seawater. 

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). 

ISOTOPES All 41 isotopes of astatine are radioactive, with half-lives ranging from 125 nanoseconds to 8.1 hours. The isotope As-210, the most stable isotope with an 8.1-hour half-life, is used to determine the atomic weight of astatine. As-210 decays by alpha decay into bismuth-206 or by electron capture into polonium-210. 

In the environment, thorium and its compounds do not degrade or mineralize like many organic compounds, but instead speciate into different chemical compounds and form radioactive decay products. Analytical methods for the quantification of radioactive decay products, such as radium, radon, polonium and lead are available. However, the decay products of thorium are rarely analyzed in environmental samples. Since radon-220 (thoron, a decay product of thorium-232) is a gas, determination of thoron decay products in some environmental samples may be simpler, and their concentrations may be used as an indirect measure of the parent compound in the environment if a secular equilibrium is reached between thorium-232 and all its decay products. There are few analytical methods that will allow quantification of the speciation products formed as a result of environmental interactions of thorium (e.g., formation of complex). A knowledge of the environmental transformation processes of thorium and the compounds formed as a result is important in the understanding of their transport in environmental media. For example, in aquatic media, formation of soluble complexes will increase thorium mobility, whereas formation of insoluble species will enhance its incorporation into the sediment and limit its mobility. 

At trace levels, polonium can be separated effectively by solvent extraction, ion exchange, paper chromatography, and other techniques. Diisopropyl ketone, di-n-octylamine, and tri-n-butylphosphate are suitable solvents for extraction. Trace amounts of polonium in solutions or sohd mixtures containing no other emitters can be determined by measuring its alpha activity. 

Beginning in 1922 she published a long series of excellent researches on polonium, in which she determined the velocity of its alpha-rays and the distribution of their lengths, and observed their ionizing power, the oscillations in their paths, and the homogeneity of their initial velocity. In 1923 she used an original method to determine the range in air of its alpha-particles. 

Reactions used for the preparation of polonium compounds are straightforward, but the experimental techniques are strictly determined by the small amount of the commonly used polonium-210 which is available and by the exceptionally high specific activity of the isotope (4.5 curics/mg, i.e., 1013 disintegrations/min/mg). Apart from the major effects of the alpha bombardment to be described, the separation of polonium-210 from its lead daughter, which grows in at a rate of 0.5%/day, constitutes a major chemical problem. It calls for rapid and efficient methods of purifying the polonium stock before each experiment the best of these is the sulfide process described in Section III. 

Self-heating, due to the stoppage of the alpha particles within the solid, is a well known phenomenon and calculation shows that the energy release from one gram of polonium metal would be about 140 watts. This high energy output affords a useful and absolute method for the rapid determination of polonium in large sources by calorimetry. 

There have been some unsuccessful attempts to prepare a volatile hexafluoride from fluorine and polonium-210 26, 104), but recently such a fluoride has been prepared in this way from polonium-208 plated on platinum 132). The product appears to be stable while in the vapor phase, but on cooling a nonvolatile compound is formed, probably polonium tetrafluoride resulting from radiation decomposition of the hexafluoride. Analytical data are not recorded for any polonium fluoride, largely owing to the difficulty of determining fluoride ion accurately at the microgram level. 

Various workers [6,7] have reviewed methods for the determination of polonium in soils. 

Radiochemical Methods for Determination of Polonium, Radiolead, Uranium, and Plutonium... 

FIGURE 11.3 Radioanalytical determination of polonium, uranium, and plutonium. 

Separation and Determination of Polonium 210Po and Lead 210Pb... 

Skwarzec, B. 1997. Radiochemical methods for the determination of polonium, radiolead, uranium and plutonium in environmental samples. Chem. Anal. (Warsaw) 42 107-115. 

Flynn, W.W. 1968. The determination of low levels of polonium-210 in environmental materials. Anal. Chim. Acta 43 221-227. 

Elements 43, Masurium 61, Illinium 84, Polonium or Radium F 89, Actinium 91, Uranium Xs do not appear in the atomic weight tables. Although their existence has been indicated by means of X-rays or radioactive properties, they have not been isolated in amounts to allow of atomic weight determination. 

Another method for measuring Volta potentials is to ionize the air between the plates, and adjust the potential applied to them until no current passes across the air gap. This method appears to have been used first by Righi2 (with ultra-violet rays as a source of ionization), later by Perrin and many later workers, using radium salts 8 Greinachcr,4 and Anderson and Morrison,6 pointed out that errors frequently arose if sources capable of ionizing the air in other parts of the apparatus than directly between the plates and it is well to use either a carefully shielded source of j3 or y rays or a radioactive source such as polonium, which gives off only a rays which have a range of a few centimetres only. This method is that used for the determination of the surface potentials of insoluble films as described in Chapter II. 

The absorption spectrum of Po in HCl solutions reveals the presence of at least two complexes, A and B. Complex A absorbs with a maximum at 344m a. Complex B absorbs with a maximum at 418 m j,. The 418m a absorption can be used for the colorimetric determination of polonium. Although the 344m j, absorption is stronger in weakly acidic solutions, it is difficult to utilize because of chlorine formation brought about by radiation from the polonium. The absorbance of the complex at 344 m a was estimated by the use of a method involving the log absorbancy curves for the complex and for the chloride ion. 

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