Polonium, natural

The more metallic nature of polonium is shown by the fact that it dissolves not only in concentrated nitric and sulphuric acids but also in hydrofluoric and hydrochloric acids. 

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. 

In 1934, scientists discovered that when they bombarded natural bismuth (209Bi) with neutrons, 210Bi, the parent of polonium, was obtained. Milligram amounts of polonium may now be prepared this way, by using the high neutron fluxes of nuclear reactors. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Radon-222 [14859-67-7] Rn, is a naturally occuriing, iaert, radioactive gas formed from the decay of radium-226 [13982-63-3] Ra. Because Ra is a ubiquitous, water-soluble component of the earth s cmst, its daughter product, Rn, is found everywhere. A major health concern is radon s radioactive decay products. Radon has a half-life of 4 days, decayiag to polonium-218 [15422-74-9] Po, with the emission of an a particle. It is Po, an a-emitter having a half-life of 3 min, and polonium-214 [15735-67-8] Po, an a-emitter having a half-life of 1.6 x lO " s, that are of most concern. Polonium-218 decays to lead-214 [15067-28A] a p-emitter haviag = 27 min, which decays to bismuth-214 [14733-03-0], a p-emitter haviag... 

Polonium has no stable isotopes, all 27 isotopes being radioactive of these only °Po occurs naturally, as the penultimate member of the radium decay series ... 

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 ... 

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 Curie (Paris) discovery of the elements radium and polonium, the isolation of radium, and the study of the nature and compounds of this remarkable element. 

Polonium, completing the elements of Group 16, is radioactive and one of the rarest naturally occurring elements (about 3 x 10 " % of the Earth s crust). The main natural source of polonium is uranium ores, which contain about lO g of Po per ton. The isotope 210-Po, occurring in uranium (and also thorium) minerals as an intermediate in the radioactive decay series, was discovered by M. S. Curie in 1898. 

Eighteen isotopes of sulfur, 17 of selenium, 21 of tellurium, and 27 of polonium have been registered of these, 4 sulfur, 6 selenium, and 8 tellurium isotopes are stable, while there is no stable isotope of polonium. None of the naturally occurring isotopes of Se is radioactive its radioisotopes are by-products of the nuclear reactor and neutron activation technology. The naturally occurring, stable isotopes of S, Se, and Te are included in Table 1.2. 

One curious observation, however, was that pure U actually had a lower radioactivity than natural U compounds. To investigate this. Curie synthesized one of these compounds from pure reagents and found that the synthetic compound had a lower radioactivity than the identical natural example. This led her to believe that there was an impurity in the natural compound which was more radioactive than U (Curie 1898). Since she had already tested all the other elements, this impurity seemed to be a new element. In fact, it turned out to be two new elements—polonium and radium— which the Curies were successfully able to isolate from pitchblende (Curie and Curie 1898 Curie et al. 1898). For radium, the presence of a new element was confirmed by the observation of new spectral lines not attributable to any other element. This caused a considerable stir and the curious new elements, together with their discoverers, achieved rapid public fame. The Curies were duly awarded the 1903 Nobel prize in Physics for studies into radiation phenomena, along with Becquerel for his discovery of spontaneous radioactivity. Marie Curie would, in 1911, also be awarded the Nobel prize in chemistry for her part in the discovery of Ra and Po. 

The liquid mine wastes are mainly represented by underground drainage waters (up to 2000 m3/day and even more), as well as low radioactive waste water from uranium treatment plants (from 100 up to 300 m3/day). The uranium isotopes, radium-226, thorium-230, polonium-210, lead-210 are the most dangerous. Their total activity in waste waters reaches often 10-50 Bq/L at the MPC values for natural waters of 0.111 Bq/L. 

Most of the known chemistry of polonium is based on the naturally occurring radioactive isotope polonium-210, which is a natural radioactive decay by-product of the uranium decay series. Its melting point is 254°C, its boiling point is 962°C, and its density is 9.32g/cm. ... 

Polonium is more metallic in its properties than the elements above it in group 16. It is the only element in group 16 that is naturally radioactive. It is in a position on the periodic table of elements where it can be a metal, metalloid, or nonmetal. It is more often considered a metal because of its electrical conductivity decreases with an increase in temperature. 

Polonium is found only in trace amounts in the Earths crust. In nature it is found in pitchblende (uranium ore) as a decay product of uranium. Because it is so scarce, it is usually artificially produced by bombarding bismuth-209 with neutrons in a nuclear (atomic) reactor, resulting in bismuth-210, which has a half-hfe of five days. Bi-210 subsequently decays into Po-210 through beta decay The reaction for this process is Bi( ) Bi — °Po + (3-. Only small commercial milligram amounts are produced by this procedure. 

Table Group VIIB (the halogens), is the earth s rarest naturally occurring element. All its isotopes are radioactive (Table I), hence the Greek name aoTaTCoC, meaning unstable 44, 45). The possibility of their existence was predicted from the -decay of polonium (55). Its three naturally occurring isotopes, At, At, and At, are the extremely short-lived natural daughters of AcA (77), RaA (76,173), and AcK (72), respectively.

Santschi PH, Li YH, Adler DM, et al. 1983. The relative mobility of natural (thorium, lead and polonium) and fallout (plutonium, americium, cesium) radionuclides in the coastal marine environment Results from model ecosystems (MERL) and Narragansett Bay. Geochim Cosmochim Acta 47 201-210. 

Polonium can be recovered from natural pitchblende. The yield, however, is exceedingly small as 1 g of polonium is contained in about 25,000 tons of pitchblende. The element may be isolated from the pitchblende extract by deposition on a bismuth plate immersed in chloride solution. 

Polonium also can be synthesized by neutron irradiation of natural bismuth in a reactor ... 

These two kinds of lead are now known to be isotopes, or inseparable elements which belong in the same space in the periodic table and yet differ in atomic weight and in radioactive properties. According to Frederick Soddy, the first clear recognition of isotopes as chemically inseparable substances was that of H. N. McCoy and W. H. Ross in 1907 (75,107). Strictly speaking, the science of radioactivity has revealed only five naturally occurring new elements with distinctive physical and chemical properties polonium, thoron, radium, actinium, and uranium X2. All the other natural radioactive elements share previously occupied places in the periodic table. 

Thus it is evident that there are three natural radioactive isotopes of thallium, seven of lead, four of bismuth, seven elements in the polonium pleiad, three inert radioactive gases, four isotopes of radium, two of actinium, six of thorium, three eka-tantalums, and three uraniums. 

Their joint papers on The numbers of ions produced by alpha rays of radium C in air were published in the Comptes rendus in 1928. In the following year they investigated the nature of the absorbable radiation which accompanies the alpha-rays from polonium. In 1930 M. Joliot presented his thesis for the doctorate, which was entitled The electrochemistry of the radio-elements, and Mme. Joliot continued her study of polonium (123). 

Pierre and Marie Curie called Becquerel s radiation radioactivity . They found that another heavy element, thorium, was also radioactive, and deduced that natural uranium ore (pitchblende) contained other radioactive elements, which they called polonium (after Marie s native country) and radium (because it glowed). After two years of sifting through tonnes of uranium ore, they isolated salts of these new elements. The work left both the Curies with hands badly scarred from radiation bums, and it no doubt hastened Marie s death from leukaemia in 1934. Pierre might have met the same fate had he not been tragically killed in a road accident in 1906. 

Unlike its lower homologues, sulfur, selenium, and tellurium, polonium has no long-lived or stable isotopes. It has, in fact, one of the most unstable nuclei of naturally occurring elements, the only readily accessible isotope being that of mass 210 this decays by alpha emission with a half-life of 138.4 days and occurs in nature as the penultimate member of the radium decay series, the last three stages being... 

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. 

In the last decade, most of the contributions to the chemistry of polonium have, rather naturally, been made by workers employed in the Atomic Energy Establishments of the United Kingdom and the United States, where milligram amounts of the element have been extracted from irradiated bismuth. Before this, all the experimental work on the element had been on the trace scale, in which quantities from 10 10 to 10 6 g were used, apart from one large source, of about 100 Mg of polonium mixed with... 

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