Radon isolation

From radium called niton at first, L. nitens, shining) The element was discovered in 1900 by Dorn, who called it radium emanation. In 1908 Ramsay and Gray, who named it niton, isolated the element and determined its density, finding it to be the heaviest known gas. It is essentially inert and occupies the last place in the zero group of gases in the Periodic Table. Since 1923, it has been called radon. 

Radon-220 [22481 8-7], Rn, a decay product of thorium, was discovered by Owens and Rutherford in 1900. The more common radon-222, a decay product of radium, was discovered later in the same year and was isolated in 1902. 

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

Element 86, the final member of the group, is a short-lived, radioactive element, formerly known as radium-emanation or niton or, depending on which radioactive series it originates in (i.e. which isotope) as radon, thoron, or actinon. It was first isolated and studied in 1902 by E. Rutherford and F. Soddy and is now universally known as radon (from radium and the termination-on adopted for the noble gases Latin radius, ray). 

Other radon-resistant alternatives besides simple isolation of the crawlspace should be considered because of the difficulties encountered in getting an adequate seal between the house and the crawlspace. These alternatives will be discussed in the next section. 

If a well has not been drilled, a nearby well may be an indicator of potential radon problems. Identifying potential radon-in-water problems by using the results from adjacent wells is subject to the same problems that were mentioned earlier. There is no guarantee that the neighbor s well is producing water with the same characteristics as the new well will produce since it may not be from the same stratum. The limited data available on houses with radon-in-water problems indicate that adjacent houses with similar wells sometimes produce similar radon-in-water problems and sometimes do not. However, few isolated radon-in-water problem houses have been observed. 

The charcoal beds must be thermally isolated from each other. The air inlets must be positioned far enough apart so as to minimize feedback of clean air back into the system. To prevent the accumulation of radon in the house in the event of a valve failure, all valves should be provided with backups. The volume of air cleaned per unit mass of carbon increases exponentially with decreasing temperature (Kapitanov et al., 1967). Thus greatly increased adsorption capacity can be obtained by cooling the carbon below ambient temperature. Although this process will require additional energy input, it may be worthwhile to consider some form of cooling. 

Radon can be isolated from radium by several methods. An aqueous solution of radium salt such as radium bromide is heated, liberating radon. Radioactive bombardment then decomposes water to oxygen and hydrogen. Radon is separated from the gaseous mixture by condensation in tiny tubes placed in liquid air. The tubes then are sealed by melting. A gold or platinum coating is applied to form the radon seeds used in radiation therapy. 

Uranium-238 emits an alpha particle to become an isotope of thorium. This unstable element emits a beta particle to become the element now known as Protactinium (Pa), which then emits another beta particle to become an isotope of uranium. This chain proceeds through another isotope of thorium, through radium, radon, polonium, bismuth, thallium and lead. The final product is lead-206. The series that starts with thorium-232 ends with lead-208. Soddy was able to isolate the different lead isotopes in high enough purity to demonstrate using chemical techniques that the atomic weights of two samples of lead with identical chemical and spectroscopic properties had different atomic weights. The final picture of these elements reveals that there are several isotopes for each of them. 

Ramsay and Rayleigh succeeded in isolating all of the noble gases except radon and in showing that they were inert to all common reagents. They also discovered the identity of alpha particles and ionized helium. 

RADON. [CAS 10043-92-2]. Chemical element symbol Rn, at. no. 86, at. wt. 222 (mass number of the most stable isotope), periodic table group 18 (inert gases), mp —71°C, bp —61.8°C. First ionization potential, 10.745 eV. Density 9.72 g/l O C, 760 torr), 7.5 x more dense than air. The gas has been liquefied at —65°C and solidified at —110°C. Radon was first isolated by Ramsay and Gray in 1908. Prior to acceptance of the present designation, radon was called niton or radium emanation. See also Radioactivity. 

Beyond element 92 (U) lie the transuranic elements of the actinide series. These are all artificial but 2< Pu is of interest because it is produced in nuclear reactors from 2 fU and may be released to the environment from accidents or weapons testing. It has a very long half life (2.4 x 104 years) and is a very dangerous alpha emitter, but, like radon, its geochemistry is too specialised to be included in this chapter. Choppin and Stout (1991) have written an overview of the general chemistry of Pu, to mark the 50th anniversary of its original isolation, and Rai et al. (1980) have discussed its soil chemistry. 

The abihty of these gases to form true chemical compounds with other atoms is limited to the heavier members of the group, krypton, xenon, and radon, where the first ionization energies are reduced to a level comparable with other chemically active elements. Theoretical studies, however, have indicated that it may be possible to isolate helium derivatives, such as MeBeHe. Many of the compounds are prepared at low temperature and characterized through spectroscopic techniques. More recently, multinuclear NMR has emerged as an extremely useful characterization technique. ... 

Within 3 years, Ramsay and M. W. Travers had isolated three additional elements by low-temperature distillation of liquid air, neon (Greek, neos, new), krypton (Greek, kryptos, concealed), and xenon (Greek, xenos, strange). The last of the noble gases, radon, was isolated as a nuclear decay product in 1902. 

Over the next decade, many scientists worked to find out more about radioactive materials. Curie and her husband, Pierre Curie (1859-1906), isolated two new radioactive elements, polonium and radium. In 1900, German physicist Friedrich Ernst Dorn (1848-1916) found a third radioactive element radon. 

The name comes from the Latin radius, meaning ray. It was discovered by Marie and Pierre Curie in 1898 when they were studying uranium and other radioactive materials found in pitchblende. There is about 1 g of radium in 7 tons of pitchblende, but it is 3xl05 times more radioactive than uranium. It was isolated as a metallic element in 1911 by Marie Curie and Andre-Louis Debieme (1874-1949). Radium exists in small quantities associated with uranium ores. Radium is phosphorescent, so it has been used to make luminous paint, especially for watch dials, but, because it is highly radioactive, most uses are related to nuclear medicine or the energy industry. Radon gas is produced from radium and is a harmful by-product. 

Already in the early days of radiochemistry some radionuclides were isolated from matrices and their mixtures were separated, making use of different volatility of various elements and compounds. Well-known is the role of the extreme volatility of radon in the discovery of emanations by Dorn and Rutherford (see a detailed story in Reference [1]). In her logbooks Mme. Curie noted purification of polonium by sublimation, when collecting deposits obtained at different temperatures [2], After the discovery of nuclear fission, the volatile species — Kr and Xe in the elemental state, As and Sb as gaseous ASH3 and SbH3, as well as Ru in the... 

The noble gases are very low-boiling gases. Except for radon, they can be isolated by fractional distillation of liquefied air. Radon is collected from the radioactive disintegration of radium salts. Table 24-1 gives the percentage of each noble gas in the atmosphere. 

In a concrete cellar an activity from radon of 200 Becquerel from 1 m of air has been measured. If the cellar walls are isolated such that no new radon is added from the walls and floor the activity will decrease with time. As the half-life for radon-222 is 3.82 days the activity after this period will be 100 Becquerel. After further 3.82 days the activity will be 50 Becquerel. 

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