Radionuclides polonium

FIGURE 11.4 Alpha spectra of polonium radionuclides (209Po and 210Po). 

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. 

Activity Determination of Polonium, Radiolead, Uranium, and Plutonium Radionuclides... 

There are three names coimected with the discovery of radioactivity Henry Bec-querel, who discovered this phenomenon in 1896 [2] Maria Sklodowska-Curie, who named this process radioactivity and her husband Pierre Curie [3]. They stated that uranium salts emit ionizing rays and, furthermore, Maria Sklodowska-Curie discovered that thorium gives off the same rays. She proved that radiation was not the outcome of some interaction of molecules, but must come from an atom itself this discovery was absolutely revolutionary. Maria and Pierre discovered the first two radioactive elements, polonium and radium. There are about 20 radioactive elements and about 50 radionuclides in the natural environment. 

Polonium is found in the natural environment, especially in uranium and thorium ores. Of seven natural radionuclides of polonium, Po is the most important. It is an alpha emitter with energy of 5.305 MeV and half-life of 138.376 days [24]. Polonium is a very radiotoxic element and undergoes strong bioaccumulation in land and aquatic organisms [1]. 

After separation and purification, the pure fractions of uranium and plutonium are electroplated on polished stainless discs and the activities of their radionuclides measured using alpha spectrometry. The distribution value of alpha detectors, which is between 17 and 20 kev, is very important. Two radionuclides ( Pu and " °Pu) are measured together because the difference between the energy of their alpha particles is less than 15 keV [1, 14]. Figures 15.3, 15.4, and 15.5 present typical spectra for the alpha measurement of polonium, uranium, and plutonium [ 1 ]. 

The errors inherent in measuring the activity of polonium, uranium, and plutonium can be assessed by determining radionuclides in CRMs in international laboratory exercises and using the CRM produced by the International Atomic Energy Agency... 

Whether in the environment or in the human body, uranium will undergo radioactive decay to form a series of radioactive nuclides that end in a stable isotope of lead (see Chapter 3). Examples of these include radioactive isotopes of the elements thorium, radium, radon, polonium, and lead. Analytical methods with the required sensitivity and accuracy are also available for quantification of these elements in the environment where large sample are normally available (EPA 1980,1984), but not necessarily for the levels from the decay of uranium in the body. More sensitive analytical methods are needed for accurately measuring very low levels of these radionuclides. 

According to Styron et al., (1979) for a realistic assessment of the magnitude of release of radionuclides, special attention needs to be given to lead-210 and polonium-210 since they appear to have a large potential for significant environmental impact and have not received sufficient attention in trace-element studies for power plants. Another potentially important parameter in determining radiation exposure to man centres on disposal and utilization of coal ash and refuse. Lee et al., (1977) have suggested that emanation of radon-222 from ash disposal ponds will be the most serious radionuclide problem associated with increased use of coal. A potential hazard can be associated with the use of fly ash in cement and concrete blocks and in roadway construction. The radium-226 in these concrete blocks used for home construction may constitute an important source of radon-222 dose to the public. 

Internally deposited naturally occurring radionuclides also contribute to the natural radiation dose from inhalation and ingestion of these materials when contained in air, food, and water. Included are radionuclides of lead, polonium, bismuth, radium, potassium, carbon, hydrogen, uranium, and thorium. Potassium-40 is the most prominent radionuclide in normal foods and human tissues. The dose to the total body from these internally deposited radionuclides has been estimated to be 39mremyear. ... 

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... 

Polonium (ii) The radioisotopes of polonium (usually Po) have been difficult to analyze with accuracy using the conventional methods. The procedure outlined here is, however, simple, rapid, and accurate. With the sample in solution, add 3 to 5 mL of concentrated phosphoric acid and evaporate to remove other acids. Transfer this phosphoric acid solution to a small equilibration vessel using 3 to 5 mL of water. Add 1 mL of 0.1 M HCl. Add a measured volume, 1.2 to 1.5 mL, of a solution of TOPO, 0.1 to 0.2 M, in toluene and equilibrate. This is a highly selective separation of polonium from other radionuclides with the possible exception of the beta/gamma emitting bismuths. Quantitative stripping and transfer of the polonium to a plate is difficult but the use of an extractive scintillator and counting on a PERALS spectrometer is rapid and simple and the results are quite accurate. Because of the minimal chemical manipulations required, the accuracy of this determination can easily be better than 1%. 

Radionuclides at very low concentrations that have a large value of 7 ° deposit spontaneously on metals that are readily oxidized in the solution. For example, polonium is routinely purified and prepared for counting by spontaneous deposition on a nickel planchet. Spontaneous deposition has been demonstrated with other metals (Blanchard et al. 1960). Polarographic separation has been achieved by reducing a radionuclide to an amalgam in a drop of mercury (Kolthoff andLingane 1939). 

As decay occurs, the remaining activity declines. The time it takes for a radionuclide to lose half its activity is its half-life (ti/2), which may range from extremely short to extremely long periods. The half-lives of polonium-214 and uranium-238, for example, are 163.7ps and 4.46x10 years, respectively. As individual isotopes decay they can form new stable or unstable isotopes in a series of steps that eventually ends in a stable nucleus. The type of decay and the half-lives of the intermediaries in a decay series is characteristic of the isotope e.g., radioactive thorium-232 undergoes the following decay steps to result in a stable isotope of lead ... 

The specific feature of LBC is the formation of a-active polonium-210 radionuclide with a half-life of 138 days when bismuth is irradiated with neutrons. 

Solving the number of principal problems on RIs reliability and safety ensuring the proper coolant quality and its maintenance in the course of operation, ensuring radiation safety associated with forming alfha-active polonium-210 radionuclide, etc. These tasks have been developed for the NS sRIs. 

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. 

As only small absolute amounts of radionuclides are to be determined, and thus only small amounts of elements are to be separated, separation cannot usually be properly performed by methods whose success depends on the amount of the component to be isolated (e.g., as in precipitation). Therefore, methods that are independent of amount (such as liquid-liquid extraction and ion-exchange methods) are more advantageous. Extraction procedures very often take advantage of additions of chelating components. For separating volatile radionuclides (such as iodine or ruthenium) from the sample matrix, distillation methods can be used advantageously. Electrolytic deposition has been shown to be applicable in the separation of polonium. 

In the uranium series, a daughter of (namely Rn) enters the atmosphere and later decays through several short-lived daughters to lead-210 with a half-life of 22.3 years (see also O Sect. 17.14 on the polonium/lead method). This radionuclide is removed by precipitation with a residence time of about 10 days. Later, this may deposit on snow and ice in glaciers as... 

The radiation safety was ensured under the generation of polonium-210 during the operation of lead-bismuth cooled reactor installations, including primary circuit equipment repair and removal of spilled lead-bismuth coolant, there was no personnel irradiation over the permissible limits for this radionuclide [XIX-3] ... 

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. 

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