Polonium abundance

Polonium is a very rare natural element. Uranium ores contain only about 100 micrograms of the element per ton. Its abundance is only about 0.2% of that of radium. 

Polonium, because of its very low abundance and very short half-life, is not obtained from natural sources. Virtually all our knowledge of the physical and chemical properties of the element come from studies on Po which is best made by neutron irradiation of in a nuclear reactor ... 

It will be recalled that is 100% abundant and is the heaviest stable nuclide of any element (p. 550), but it is essential to use very high purity Bi to prevent unwanted nuclear side-reactions which would contaminate the product Po in particular Sc, Ag, As, Sb and Te must be <0.1 ppm and Fe <10ppm. Polonium can be obtained directly in milligram amounts by fractional vacuum distillation from the metallic bismuth. Alternatively, it can be deposited spontaneously by electrochemical replacement onto the surface of a less electropositive metal... 

Radon-222 also undergoes radioactive decay and has a radioactive half-life of 3.8 days. Radon-220 and -219 have half-lives measured in seconds and are not nearly as abundant as Radon-222. Thus the discussion of radon health effects here centers on Radon-222. Radon-222 decays into radon daughters or progeny, which are radioactive elements. Two of these (polonium-218 and polonium-214) emit alpha particles (high-energy, high-mass particles, each consisting of two protons and... 

The rarity of polonium is evident from a calculation (1) which shows that the outermost mile of the earth s crust contains only 4000 tons of the element, whereas radium, usually classed as rare, is present to the extent of 1.8 X 107 tons. The abundance of polonium in uranium ores is only about 100 Mg per ton and hence separation of the element from such mineral sources cannot seriously be considered. However, radium, at equilibrium with its daughters, contains 0.02 wt % of polonium and, until recently, most of the element was obtained either from radium itself or, more usually, from expended radon ampoules which, after the radon decay is complete, contain radium-D and its daughters. Fortunately, however, the parent of polonium in these sources, bismuth-210, can be synthesized by neutron bombardment of natural bismuth [Bi209 (n,y) Bi210] and with the advent of the nuclear reactor it has become practicable to prepare milligram amounts of polonium. Almost all of the chemistry of the element recorded in the recent literature has been the result of studies carried out with polonium-210 prepared in this way. 

Fig. 15.1 Relative abundances of the group 16 elements (excluding Po) in the Earth s crust. The data are plotted on a logarithmic scale. The units of abundance are parts per billion (1 billion = 10 ). Polonium is omitted because its abundance is only 3 X 10 ppb, giving a negative number on the log scale.

Polonium is found in the earth s crust at exceedingly low levels its natural abundance is only 2 x 10 ° milligrams per kilogram. Polonium is produced in pitchblende when the bismuth isotope °Bi, which has a half-fife of five days, decays into °Po. Approximately 100 micrograms of polonium are found in 1 ton of uranium ore. Polonium can also be produced by bombarding ° Bi with neutrons to form °Bi, which in turn decays into °Po. 

Even in case of lead coolant the problem of polonium contamination exists because of Bi-209 formation by neutron capture in Pb-208 (abundance 52.3%) [7.5] ... 

We have already discussed the history of discovery of two natural radioactive elements, that is, uranium and thorium, in Chapter 4. These elements can fairly easily be found in minerals with chemical analysis since their content is sufficiently high. Other natural radioactive elements (polonium, radon, radium, actinium, and protactinium) are among the least abundant elements on Earth. Moreover, they exist in nature only because they are the products of radioactive transformations of uranium and thorium. 

Radon is a colorless, odorless and radioactive gas, the heaviest of all gases. Rn, the most abundant isotope of radon, has a half-life of 3.8 days and decays into an isotope of the element polonium. After inhalation of radon, this radionuclide stays locked in the tissues, e.g. in the lungs. Because of that, radon from the surrounding soil and rocks has become a safety issue around the world. 

Polomnm—(Poland,nativecountryofMme.Cutie[1867-1934]),Po at.wt. (209) at. no. 84 m.p.254°C b.p. 962°C sp.gr. (alpha modification) 9.32 valence-2,0, +2, +3(7), +4, and+6. Polonium was the first element discovered by Mme. Curie in 1898, while seeking the cause of radioactivity of pitchblende from Joachimsthal, Bohemia. The electroscope showed it separating with bismuth. Polonium is also called Radium F. Polonium is a very rare natural element Uranium ores contain only about 100 tg of the element per ton. Its abundance is only about 0.2% of that of radium. In 1934, it was found that when natural bismuth ( Bi) was bombarded by neutrons, Bi, the parent of polonium, was obtained. Milligram amounts of... 

Pure lead is not completely exempt firom polonium formation because Pb (the most abundant natural isotope of lead) transmutes into Bi, and Po is eventually produced from neutron capture by ° Bi. The rate of polonium production in pure lead is, however, much lower than in the case of LBE, and it is negligible in terms of decay heat power. In fact, the polonium inventory at equilibrium in the primary system of a 1500 MWth, pure lead-cooled reactor (ie, ELSY) has been calculated to be less than 1 g after 40 years of irradiation (Cinotti et al., 2011). 

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