Radioactive polonium

The experimenters set up a lead-shielded box containing radioactive polonium, which emitted a beam of positively charged subatomic particles through a small hole. Today, we know that the particles of the beam consisted of clusters containing two protons and two neutrons and are called alpha particles. The sheet of gold foil was surrounded by a screen coated with zinc sulfide, which glows when struck by the positively charged particles of the beam. 

Rutherford s lead-shielded box contained radioactive polonium. As polonium decays, it emits helium nuclei, which consist of two protons and two neutrons. These nuclei are called alpha particles. Because they have no electrons, they are positively charged. 

Oxygen (O) and sulfur (S) are among the most important elements in industry, the environment, and organisms. Selenium (Se), tellurium (Te), radioactive polonium (Po), and newly synthesized element 116 lie beneath them in Group 6A(16) [Family Portrait, p. 444]. 

The major reason for its radiation danger is the formation of radioactive polonium aerosols when hot LBC contacts with air. It could happen under conditions of emergency tightness loss of the primary circuit and coolant spillage. In this case, as the RI operation experience at the NS has displayed, the yield of Po aerosols and air radioactivity (according to the thermodynamics laws) reduce quickly with temperature decreasing and spilled alloy solidifying. Fast solidification of spilled LBC restricts the area of radioactive contamination and simplifies its removal in the form of solid radioactive wastes. 

Now let us turn back to the last decades of the 19th century. When Mendeleev developed the periodic system of elements it contained many empty slots corresponding to unknown elements between bismuth and uranium. These empty slots were rapidly filled after the discovery of radioactivity. Polonium, radium, radon, actinium, and finally protactinium took their places between uranium and thorium. Only eka-iodine and eka-cesium were late. This fact, however, did not particularly trouble scientists. These unknown elements had to be radioactive since there was not even a hint of doubt that radioactivity was the common feature of elements heavier than bismuth. Therefore, sooner or later radiometric methods would demonstrate the existence of elements 85 and 87. 

Because of its intense radioactivity, polonium has been less studied than the other chalcogens, and the chemical consequences of the inert-pair effect, primarily a sixth-period phenomenon, remain largely unexplored for polonium. 

Uranium is another example of a contaminant often found in phosphate fertilizers. Also, highly radioactive Polonium-210 contained in phosphate fertilizers is absorbed by the roots of plants and stored in its tissues tobacco derived from plants fertilized by rock phosphates contains Polonium-210 which emits alpha radiation estimated to cause lung cancer. 

Similar to the other groups that have been presented, group 16 (VI A) (the chal-cogens or the oxygen family) starts with an element whose physical properties and chemical reactivity do not resemble those of the rest of the group. Here also, the metallic character increases down the group oxygen and sulphur are nonmetals, selenium and tellurium are considered metalloids (they are referred to as a metal when in elemental form), while radioactive polonium is classified either as a post-transitional metal or metalloid (Hawkes 2010 Bentor 2011). 

The last two chalcogens from Group 16 (VIA) to be considered are selenium and tellurium, both of which resemble sulfur to some extent. Radioactive polonium not is considered since it is radioactive and extremely rare. 

Corrosion of candidate materials for stills to separate radioactive polonium-210 from bismuth by distillation at temperatures of 450-950°C has been investigated. Tellurium, which is chemically similar to polonium, was used as a nonradioactive simulant. Of the materials tested, tantalum was the most satisfactory from the standpoints of fabricability and long-term corrosion resistance. Tantalum corroded at rates up to 2X10 mph during the initial 100-200 h of exposure, and the rate decreased to less than 2 X10 mph for 400 h for concentrations of tellurium of less than 30% in bismuth. 

Now that we have some understanding of the way in which the decay scheme works, we can look back and understand some of the difficulty Marie Curie had in isolating radioactive polonium (named for her home country of Poland). Using modem data from Ref. [1], we find t /2 = 3.53h for the electron capture of g Po Bi followed by another electron capture by Bi Pb with h/2 = 11.2h to form stable Pb. Although other isotopes are involved, this scheme shows the difficulty in isolating Po from Bi while the decay process is going on. Note that the time scale in Figure 7.6 is in hours. 

The other possibility is a liquid metal. Mercury was used in an experimental reactor in America, but the use of mercury poses some obvious hazards. A lead bismuth alloy is a possibility, since it has a low melting point (having the coolant freeze in the reactor is not a good move) but bismuth absorbs neutrons and decays to become radioactive polonium. The only other feasible option is to use sodium... 

---