Polonium after decay

Marie Curie discovered the element polonium, Po, in 1898. She named polonium after Poland, her homeland. Curie won two Nobel Prizes, one in Physics (1903) for sharing in the discovery of radioactivity, and one in Chemistry (1911) for the discovery of radium, which has been used to treat cancer. Radium-226 undergoes alpha decay to yield radon-222. 

Polonium-210 decays by alpha emission and has a half-life of 138 days. Suppose a sample of Po-210 contains 6.02 X 10 Po-210 atoms and undergoes decay for 138 days. What was the mass in grams of the original sample Assume all alpha particles formed by the decay escape, and the daughter nuclei remain in the sample as nonradioactive isotopes then calculate the mass of the sample in grams after 138 days. 

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. 

The final member of the group, actinium, was identified in uranium minerals by A. Debieme in 1899, the year after P. and M. Curie had discovered polonium and radium in the same minerals. However, the naturally occurring isotope, Ac, is a emitter with a half-life of 21.77 y and the intense y activity of its decay products makes it difficult to study. 

Marie (NLP 1903, NLC 1911 ) and Pierre (NLP 1903 ) Curie took up further study of Becquerel s discovery. In their studies, they made use of instrumental apparatus, designed by Pierre Curie and his brother, to measure the uranium emanations based on the fact that these emanations turn air into a conductor of electricity. In 1898, they tested an ore named pitchblende from which the element uranium was extracted and found that the electric current produced by the pitchblende in their measuring instrument was much stronger than that produced by pure uranium. They then undertook the herculean task of isolating demonstrable amounts of two new radioactive elements, polonium and radium, from the pitchblende. In their publications, they first introduced the term radio-activity to describe the phenomenon originally discovered by Becquerel. After P. Curie s early death, M. Curie did recognize that radioactive decay (radioactivity) is an atomic property. Further understanding of radioactivity awaited the contributions of E. Rutherford. 

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. 

The extraction of polonium from uranium ores is now only of historical interest. The trace level amounts used in the earlier work were usually obtained either from the lead residues of uranium ore processing, which contained lead-210, or, more commonly, from aged radon ampoules which, after the complete decay of the radon, contained Pb210, Bi210, Po210, and... 

Radon itself is radioactive however, its radiation is not the major problem. Because it is a gas and chemically inert, it is rapidly exhaled after breathing. However, radon decays to polonium ... 

By 1898 Madame Curie and her husband Pierre, in collaboration with Bequerel, had isolated two new elements from the radioactive decay of uranium in pitchblende ore. Both were more radioactive than uranium itself. They named the first element polonium (Po) after Madame Curie s native land (Poland), and the second was named radium (Ra). Isolation of these two elements required chemical separation of very small amounts of Po and Ra from tons of pitchblende. Radium was found to be over 300,000 times more radioactive than uranium. 

Very soon after the radioactivity of thorium and uranium had been discovered it was found that pure samples of both of these elements were only very weakly radioactive. However, such pure samples became more and more radioactive with time until they reached a steady level identical to that in the original samples before pmification. This suggested that the uranium or thorium atoms were transforming or decaying into other radioactive daughter elements and that hitherto undiscovered series of such elements might exist. The search for the radioactive products of uranium by Marie and Pierre Curie led to the characterisation of two new elements, which were named polonium, Po, and radium, Ra. Both elements are far more radioactive than uranium and decay so rapidly that no ore deposits are formed. They exist only because they are formed constantly from naturally occurring uranium. 

When an element has more than one radioisotope, determinations and data analysis are generally more complex because the isotopes may differ in half-life, especially when a series is involved, e.g., radium, thorium, polonium, radon, actinium, protactinium, and uranium. One possibility is to make measurements after the decay of the short-lived radionuclides, but this may require long waiting times. In favorable cases, it is more convenient to measure the activity of decay products (e.g., radon, thoron ( Rn), actinon ( Rn)), or correct the measurements of the short-lived radioisotopes after determination of the isotopic composition. 

Some tonnes of raw material had been treated. The amount precipitated by electrolysis was 0.002 g, with an estimated quantity 0.0001 g of a new element. This new element was given the name polonium (Po) after Marie s native country. Polonium was the first element whose discovery was based on radioactive measurements. The isotope found in Curie s and Debierne s investigations was °Po with a half-life of 138 days. In nature polonium exists only in equilibrium with its mother substances in different decay series. If separated from its environment, it disintegrates to lead. 

The polonium production in an LBE-cooled reactor is so high that in the 80 MW, LBE-cooled ADS developed in the 5th Framework Program of Euratom, the polonium inventory within the primary coolant circuit was evaluated to be 2 kg at equilibrium. This amount of polonium generates a decay heat in the primary system that, 5 days after a reactor shutdown, would equal the decay heat power of the fuel itself (Cinotti et al., 2011). 

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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