213 10 Radioactive Labeling in Experimental Aerosol Research Kvetoslav R. Spurny CONTENTS Introduction 213 Laboratory Methods of Preparing Radioactively Labeled Aerosols 214 Labeling by Means of Decay Products of Radon and Thoron 214 Ultra-fine Aerosols by Radiolysis 215 Labeling by Means of Radioactive Gases 217 Labeling by Means of Radioactively Labeled Elements and Compounds 218 Equipment and Procedures 219 Labeling by Means of Radiolabeled Condensation Nuclei 222 Radioactively Labeled Carbonaceous Aerosols 226 Radioactively Labeled Fibrous Mineral Aerosols 228 Radioactive Labeling of Sampling Filters 231 Radioactive Aerosol Labeling in Animal Inhalation Toxicology and Medical Research 234 Animal Inhalation Toxicology 235 Generation Techniques 235 Radioactively Labeled Model Aerosols in Human Medicine 236 Choice of Particles and Radiolabel 236 Radiolabeled Aerosols for Ventilating Imaging 237 Radioactive Labeling of Atmospheric Aerosols 238 Labeling by Decay Products of Radon and Thoron 238 Labeling by Cosmic Radiation 238 Labeling by Artificial Radioactivity 238 Fission Products 238 Industrial Sources 239 Nuclear Power Plants 239 Chernobyl Aerosol Characterization 239 Radiolabeled Atmospheric Aerosols and Radiation Smog 239 References 243 INTRODUCTION From an experimental point of view, in studying physical, chemical, and biological behavior and effects of solid and liquid aerodisperse systems under atmospheric and laboratory conditions, the application of radioactive labeling procedures is very useful. Radioactive aerosols and radioactively labeled aerosols have existed in nature probably as long as our planet has existed. In 1995, Renoux published an overview of the history of the natural atmospheric radioactivity. The discovery of the rare radioactive gas radon is attributed to Pierre L829/frame/ch10 Page 213 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC 214 Aerosol Chemical Processes in the Environment and Marie Curie in 1898 and Dorn in 1900. Thoron ( 220 Rn) was discovered by Rutherford and Owens in 1899–1900, and actinon ( 219 Rn) by Debierne and Geisel about the same time. The first scientist to find radioactive aerosols was Marie Curie in 1905. 2 She studied the influence of gravitational field on the decay products of radon. Radon’s radiotoxicity was first studied in France in 1904 by Bouchard and Balthazard, and in 1924 it was hypothesized that the great mortality observed in uranium mines of Schmeeberg in Germany and Joachimsthal in Czechoslovakia was due to radon. In 1939, Read and Mottram found that radioactive aerosols are biologically more effective than radon itself. 2,3 Elster and Geitel were the first to see (in 1901) that radioactivity is present in the atmosphere. 1 Since World War II, radioactive aerosols have become well known, and the object of increasing studies and use. Their physical properties and effects started to be intensively studied in the 1950s. Wilkening estimated the size distribution of the natural radioactive aerosols in the atmosphere in 1952 and, in 1959, Jacobi found that more than 50% of the natural atmospheric radioactivity is deposited on aerosol particles smaller than 0.2 µ m. The first theory of small particle labeling by radioactive ions was developed by Bricard in 1949. The exploitation of radioactive labeling in aerosol research also dates back to the 1950s. Nevertheless, a very fast development started about ten years later. 3 Since that time, basic theoretical investigations have led to a complex description of the nuclear methods applied in physical and chemical research. 4 What is the difference between a radioactive aerosol and a radioactively labeled aerosol? There may be no precisely definable difference. From a historical point of view, all radioactively labeled aerosols in the atmosphere and space are called radioactive aerosols. But from a radiochemical point of view, for aerosols used in the laboratory conditions, it is best to use the expression “radioactively labeled aerosols.” This means that only some aerosol particles are radioactive, and that only a portion of each particle is in fact radioactive. In contrast, the expression “radioactive aerosol” means that all particles are radioactive, and that each particle consists predominantly of radioactive species. LABORATORY METHODS OF PREPARING RADIOACTIVELY LABELED AEROSOLS Different methods can be used in the preparation of radioactively labeled aerosols under laboratory conditions. The most important labeling methods for practical and laboratory purposes are listed in Table 10.1. Neutron activation of the aerosol itself (method 1) is not very suitable or economical, and therefore will not be discussed here. The most suitable methods are those in which the aerosol is first prepared with the desired properties, and the particles are then labeled by condensing a radioactive substance on their surfaces (methods 2 and 3). Another convenient method for preparing radioactively labeled aerosols involves condensation or dispersion of radioactive substances (method 4). The processes of preparing radioactive nuclei (method 5) and preparing condensation aerosols can be combined. L ABELING BY M EANS OF D ECAY P RODUCTS OF R ADON AND T HORON This method is used very often and is similar to the natural radioactive labeling of fine aerosol particles in the atmosphere. Through a diffusion process, the natural aerosols are labeled by means of radon and thoron decay products. 3 The relative distribution of the activity on particles of different sizes was first described by Lassen in 1965. 5 This distribution function was constructed assuming the validity of Junges’s distribution of natural aerosols, 6 including the condition of coagulation (see Table 10.1). Wire screen diffusion batteries have been found to be the most suitable method for measuring the activity size distribution of radon and thoron progeny. 7-9 L829/frame/ch10 Page 214 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC Radioactive Labeling in Experimental Aerosol Research 215 The short-lived decay products of 222 Rn and 220 Rn are formed initially in an atomic, positively charged state that rapidly combines with submicron (mainly with nano-sized) aerosols. The resulting ultra-fine aerosols consist of a complex mixture of charged and neutral particles. Under normal conditions, the average electrical charge of the 222 Rn and 222 Rn progeny atmosphere is substantially less than one elementary unit. The electrical charge distribution is mostly symmetrical. 10-13 The decay-product method of labeling is relatively easy to use in the laboratory. An artificial inactive aerosol is passed through a cylinder filled with radon or thoron. When aerosol particles remain in this atmosphere for a sufficient length of time, they become alpha-radioactive. It should be noted, however, that if concentrations of thoron greater than about 1 µ Ci (27 kBq)/liter are used, aerosols may be produced by radiolytic reactions with impurities in the air. these may also become labeled with ThB and confuse the picture. 3 Ultra-fine Aerosols by Radiolysis It has been reported for many years that condensation nuclei can be produced by ionizing radiation. For example, radiolysis following the decay of 222 Rn results in the production of ultra-fine aerosols. Recent studies were able to improve the measurement of activity size distribution of these ultra- fine particles produced by radon and its daughters. It has been found that the activity that was conventionally referred to as the “unattached” fraction is actually an ultra-fine particle aerosol from water molecule radiolysis with a size range of 0.5 nm to 3 nm. 14 Oxidizable species such as SO 2 react promptly with hydroxyl radicals and form a condensed phase. These molecules coagulate and become ultra-fine particles. The size distribution of these ultra-fine particles can be shifted upward with the increase of SO 2 concentrations. Further investigation 13 showed that 218 Po formed — during radon decay in well-controlled composition atmospheres (e.g., N 2 ) — clusters in the size range between 0.7 nm and 2.0 nm. Figure 10.1 shows the diagram of such a 218 Po cluster generation system. The size of the produced clusters could be efficiently measured by means of a SMEC ( spectrometre de mobilite electrique circulaire ) device. The clusters formed in the radiolysis of radon include progeny particles and nonradioactive particles. In more recent investigations, the activity size distributions of 212 Pb- and 212 Bi-borne nanometer particles were produced and measured. When thoron gas enters the spherical chamber (Figure 10.2), it soon decays to 212 Pb and can be oxidized. Since most 212 Pb ions have positive charge, they attract polar molecules and form clusters. The cluster sizes measured by means of a diffusion battery (DB) were less than 2 nm. 9 TABLE 10.1 Some Methods for Preparing Radioactively Labeled Aerosols 1. Preparation by means of neutron activation of aerosols in a nuclear pile or other neutron source (not very suitable). 2. Labeling by means of decay products of radon and thoron. Relative distribution of activity on particles of different sizes (L. Lassen): A ( r ) d r = Φ ( r ) N ( r ) d r 3. Labeling by means of radioactive gases (Rn, Tn, Xe, etc.) in high-frequency discharge at low pressure. 4. Preparation by means of radioactively labeled elements and compounds (condensation aerosols, disperse aerosols, and plasma aerosols). 5. Preparation by means of radioactively labeled condensation nuclei . L829/frame/ch10 Page 215 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC 216 Aerosol Chemical Processes in the Environment FIGURE 10.1 Schematic diagram showing the system for the generation of 218 Po cluster aerosols. (From Mesbah, B., Fitzgerald, B., Hopke, P.K., and Pouprix, M., Aerosol Sci. Technol., 27, 381-393, 1997. With permission.) FIGURE 10.2 Experimental setup for the generation and measurement of nanometer-sized 212 Pb- and 212 Bi- borne particles. (From Chen, T.R., Tung, C.J., and Cheng, Y.S., Aerosol Sci. Technol., 28, 173-181, 1998. With permission.) L829/frame/ch10 Page 216 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC Radioactive Labeling in Experimental Aerosol Research 217 L ABELING BY M EANS OF R ADIOACTIVE G ASES This method consists of exposing an aerosol or an aerosol sample to a high-frequency discharge at low pressure in a mixture of radon, krypton, or xenon, etc., and air. The atoms of a radioactive gas, ionized and accelerated in the electric discharge, penetrate and are retained on the surface of the aerosol particles. The method of labeling has two attractive features. First, the position of individual particles can be determined by autoradiography. When radon is used for labeling and radiography is carried out with nuclear emulsion, individual particles show up in the radiogram as stars consisting of the tracks of alpha-rays (Figure 10.3). The frequency of the tracks in each star is an indication of the particle’s size. Second, the action of a suitable gaseous medium (a chemical surface reaction) on the aerosol particles can release the radioactive gas from the aerosol sample. This feature provides the possibility of chemically identifying individual particles in the aerosol sample. An aerosol can be activated directly in a suspended state, independent of its chemical compo- sition, in a stream of gas. By repeated measurements of aerosol activity, the aerosol concentration can be measured continuously. Labeling with decay products of radon is most suitable for these purposes, because the radon is not used in gaseous form and is attached to the surface of the solid substances. Radon can be firmly fixed, for example, on the inner wall of a glass tube with the aid of an electric discharge at low pressure. 15,16 The radon is retained near the surface and a large proportion of the RaA atoms originating from the decay are ejected by recoil into the gas inside the tube. Because of their low energy, these atoms traverse a small distance, roughly 0.1 mm; and if the air is free of aerosols, they quickly diffuse back to the surface of the tube, where they are retained. If the air contains aerosol particles, however, some of the RaA atoms are retained by the aerosol; and the retention of RaA atoms increases with increasing concentration of the aerosol. An instrument for continuous measurements of inactive aerosol concentration, based on this principle, was built and described by Jech in 1963. 16 The function of the instrument is shown schematically in Figure 10.4. The aerosol sample in air flows at a speed of roughly 0.25 1/min through the activating tube (A), which contains 5 to 10 mCi (185 to 370 MBq) radon. The activated aerosol emerges from the tube, is filtered by a Millipore filter (F), and its activity is measured differentially. The activity of the filter was continuously measured by a Geiger-Müller counter (in its proportional region); and the counts were integrated and registered by the ratemeter (Rm) and FIGURE 10.3 The tracks of alpha-rays from single aerosol particles. L829/frame/ch10 Page 217 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC 218 Aerosol Chemical Processes in the Environment recorder (Rg). The relative amount of RaA atoms retained by individual particles was dependent on the size of the particles as well as on the numerical concentration of the aerosol. Therefore, the instrument had to be calibrated for an aerosol of given dispersity. 17 L ABELING BY M EANS OF R ADIOACTIVELY L ABELED E LEMENTS AND C OMPOUNDS In this case, there are two principle possibilities: (1) preparation of dispersed aerosols by spraying or nebulizing solutions or powders; and (2) preparation of condensation aerosols by spontaneous vapor condensation, or vapor condensation in the presence of radioactive condensation nuclei. The first method has some disadvantages: the possibility of contamination is great; the con- sumption of radioactive material is large; and the aerosol particles show little specific radioactivity. Nevertheless, it was used in some cases to great effect in the 1960s and thereafter. 18 However, the second possibility — the use of condensation methods — provides highly dispersed aerosols, approximately monodisperse, and the particles show a high specific radioactivity. Through the nucleation process, the particle size and the aerosol concentration can be changed by changing the supersaturation of the vapor. From nucleation theory, it is known that the particle concentration for a given time is an exponential function of the supersaturation of a vapor. This supersaturation is controlled in practice by changing the evaporation temperature of the substance and the flow rate of dilution gas. When all conditions are constant, the concentration can be calibrated and the particle size determined as a function of evaporation temperature and gas flow, the particle size being measured with an electron microscope, diffusion battery, etc. 19 The chemical elements and compounds for preparing condensation aerosols have to be stable; they should not decompose on heating. Evaporation is often accompanied by oxidation, so that the aerosol being prepared becomes oxidized. Tables 10.2 and 10.3 describe the elements and inorganic and organic compounds that are suitable for preparing condensation aerosols and which are easy to label with different radioisotopes. Table 10.4 shows more detail concerning some radioactively labeled inorganic condensation aerosols that were described and used in laboratory experiments in the 1960s. 19-27 FIGURE 10.4 Schematic diagram of apparatus for continuous recording of aerosol concentration, and an example (inset) of a recording that shows aerosol concentration in unfiltered and filtered air from the laboratory. A = activating tube; F = Millipore ® filter; GM = Geiger–Müller tube; Rm = ratemeter; Rg = recorder; S = lead shield; D = revolving metal disk; P = pump; CPM = counts per minute, t = time. L829/frame/ch10 Page 218 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC Radioactive Labeling in Experimental Aerosol Research 219 Equipment and Procedures Different kinds of equipment can be used for spontaneous condensation under constant conditions. Three of them have proven to be very suitable for the generation of highly dispersed radiolabeled condensation aerosols. Such model aerosols make it possible to measure more rapidly and sensi- tively numerous processes in the mechanics of aerosols (e.g., coagulation, phase transformation, filtration, deposition, etc.). TABLE 10.2 Inorganic Material Suitable for Preparing Radioactively Labeled Condensation Aerosols Element or Compound Melting Point (°C) Temperature (°C) at Vapor Pressure 10 –5 mmHg Hg –38.9 126.2 H 2 SO 4 10.5 145.8 Ga 30 1349 H 4 P 2 O 7 61 — Se 217 356 Re 2 O 7 296 215.5 Tl 303.5 825 SeO 2 340 157 Te 452 520 AgCl 455 912 BeI 2 488 283 PbCl 2 501 547 LiF 547 1047 AgI 552 820 CsI 621 738 CsBr 636 748 CsCl 646 744 NaI 651 767 V 2 O 5 690 — NaCl 800 865 Ag 961 767 Au 1063 1083 Mn 1244 717 Be 1284 942 Si 1410 1024 Ni 1455 1157 Co 1478 1249 Fe 1535 1094 V 1710 — Pt 1774 1606 Cr 1900 907 SrO 2430 2068 Mo 2622 1923 Os 2697 2101 Ta 2996 2407 W 3382 2554 L829/frame/ch10 Page 219 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC 220 Aerosol Chemical Processes in the Environment Furnace Generators The apparatus for the generation of condensation aerosols by sublimation of the solid phase or by evaporation of the liquid phase or inorganic substances consists of an electric furnace in which the substance under study is heated to an adjustable and controlled temperature. The dry gas passing through the furnace at an adjustable flow rate is enriched with the vapor or aerosol particles of the same substance used. After passing through the furnace, the gas with aerosol particles is led into a condenser and then into a homogenizer. Several types of furnace, each specially designed for an individual aerosol or aerosol group, proved suitable. 19-27 A longitudinal furnace (Figure 10.5) was employed to prepare sodium chloride aerosols. 19 A ceramic tube was heated by two electric coils. In the first part of this tube, radiolabeled NaCl [ 24 Na, 10 to 500 mCi (370 MBq to 18.5 GBq)] was heated to the desired temperature in a porcelain boat. The second part of the tube was heated to a temperature about 10% higher than that in the first part. A vertical furnace (Figure 10.6) was employed to prepare silver iodide aerosols. The furnace consisted of two halves that were heated by electric, ceramic heating elements with a power output of 800 W. The gas entered the space over the substance (AgI) in the middle of a sealed silica tube. The vapor and the aerosols of silver iodide were drawn off from the upper part of the furnace. The yellow powder of AgI was added through a wider tube into a platinum crucible placed on the bottom of the tube. The AgI can be radiolabeled by 131 I or by 110 Ag. For substances with a low melting point or high vapor pressure (e.g., Se, SeO 2 , H 2 SO 4 , H 4 P 2 O 7 ), an apparatus with a double glass orifice was found suitable (Figure 10.7). Here, a vapor was condensed in a gas stream. After going through the double orifice (2), the vapor and cold clean gas were combined in the mixing reservoir (5). The produced aerosols were radiolabeled by 35 S, 75 Se, and 32 P. 19 TABLE 10.3 Organic Compounds Suitable for Preparing Condensation Aerosols (Radioactive Labeling by Means of Radioactive Condensation Nuclei) Compound Formula Melting Point (°C) Temperature (°C) at Vapor Pressure 1 mmHg Dichloro-1-naphthylsilane C 10 H 8 C l2 Si — 106.2 Trethylene glycol C 6 H1 4 O 4 — 114.0 Tetraethylene glycol C 8 H 18 O 5 — 153.9 Nitroglycerine C 3 H 5 N 3 O 9 11.0 127.0 Capric acid C 10 H 20 O 2 31.5 125.0 Palmitic acid C 16 H 32 O 2 64.0 153.6 Diacetamide C 4 H 7 NO 2 78.5 70.0 Glutaric acid C 5 H 8 O 4 97.5 155.5 Acridine C 13 H 9 N 110.5 129.4 Resorcinol C 6 H 6 O 2 110.7 108.4 Sebacic acid C 10 H 18 O 4 133.0 — Adipic acid C 6 H 10 O 4 152.0 159.5 Hydroquinone C 6 H 6 O 2 170.3 132.4 Benzanthrone C 17 H 10 O 174.0 225.0 Hexachlorobenzene C 6 C l6 230.0 114.4 Dioctyl sebacate C 26 H 50 O 4 —— Dioctyl-phthalate C 18 H 30 O 4 —— Dibutyl-phthalate C 16 H 22 O 4 —— L829/frame/ch10 Page 220 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC Radioactive Labeling in Experimental Aerosol Research 221 Wire Generators Aerosol generators in which metal wires can be evaporated have also proved very suitable. This type of condensation aerosol generator produces a constant concentration of aerosol particles and constant particle sizes; these are reproducible. Furnace generators require a few hours before they work stably. On the other hand, wire generators, 10 minutes after they are turned on, produce constant particle sizes. The preparation of radioactively labeled aerosols from platinum wire and nickel-chromium wire were reported in the middle of the 1960s. 28,29 The principle of such a generator is shown in Figure 10.8. Clean, dry, and preheated air (G) flows across a platinum wire, which is heated electrically. The produced aerosols can be labeled by 197 Pt and 199 Au. Similarly, other types of metal wires have been found suitable, such as Re ( 186 Re, 188 Re), Au ( 198 Au), etc. 22 Another apparatus that can be used for preparing radiolabeled aerosols by wire evaporation is a “plasma” aerosol generator. 30 The principle of this method is shown in Figure 10.9. The tungsten or platinum wire (W) is exploded using energy stored in a bank of condensers (about 30 J). Such wire explosions are possible in atmospheres of various gases. 31 Sintering Metal Generators Highly dispersed silver aerosols have found useful applications in various physical, chemical, and biological investigations. Generation procedures for this metallic aerosol have been reported in several publications since the middle 1970s. 32 TABLE 10.4 Radioactively Labeled Inorganic Condensation Aerosols Compound or Element a Temperature Range (°C) Range of Particle Radii (µµ µµ m) Radioactive Isotopes (half-life) Pt-oxides, mo, s 600–1300 5 × 10 –3 –3 × 10 –2 197 Pt (18 h) 199 Au (3 d) Ag, s 600–1300 2 × 10 –2 –2 × 10 –1 110 Ag (249 d) Au, s 700–1200 10 –2 –10 –1 198 Au (2.7 d) WO 3 , N 2 , mo, s 900–1200 2 × 10 –2 –8 × 10 –2 185 W (73 d) NaCl, mo, s 400–1100 3 × 10 –3 –10 –124 Na (15 h) 22 Na (2.6 y) V 2 O 5 , s 400–950 5 × 10 –2 –1.5 × 10 –150 V (6 × 1014 y) Se, N 2 , mo, s 150–300 3 × 10 –2 –3 × 10 –175 Se (27 d) Te, N 2 , mo, s 200–300 10 –2 –5 × 10 –2 127 Te (105 d) Re(Re 2 O 7 ), s 100–350 4 × 10 –3 –3 × 10 –2 High spec. act. 186 Re (90 h) 188Re (17 h) AgI, N 2 , mo, s 200–600 5 × 10 –2 –3 × 10 –1 131 J (8 d) 110 Ag (249 d) H 4 P 2 O 7 , s 150–300 10 –2 –10 –132 P (14 d) H 2 SO 4 , l 50–200 10 –1 –10° 35 S (87 d) Hg, N 2 , l 50–200 5 × 1 0–1 –10 –1 203 Hg (48 d) AgCl, s, N 2 350–1000 10 –2 –7 × 10 –1 110 Ag (249 d) Fe(Fe 2 O 3 ), s, air 450–800 2 × 10 –3 –1.5 × 10 –255 Fe (2.5 y) GaCl 3 , s, N 2 , air 60–200 0.4–2.5 67 Ga (78 h) S, s, He 50–200 10–1 –5 × 10 –135 S (87.6 d) Tl, s, N 2 300–700 2 × 10 –3 –5 × 10 –3 204 Tl (3.9 y) a mo = monodisperse aerosol; s = solid; l = liquid. L829/frame/ch10 Page 221 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC 222 Aerosol Chemical Processes in the Environment Sutugin et al. 33-36 have developed a fundamental theoretical basis for the nucleation of metal and metal oxide molecules, and their results were later exploited for practical aerosol preparation. The Ag-aerosol can be easily radiolabeled. At the end of the 1970s, Spurny developed and described a generator for highly dispersed (Ag + 110 Ag) aerosols. 27 In this generator, disks of sintered silver particles (produced as “silver membrane filters” by Flotronics, U.S.) were used as the initial material (Figure 10.10). The disks were labeled with 110 Ag by neutron activation. A schematic and a photograph of the apparatus for preparation of condensation aerosols of radiolabeled silver are shown in Figure 10.11. The silver filter disk (Ag) was heated by electric current. Nitrogen, helium, or argon was used as the inert gas. Approximately monodisperse radio- labeled aerosols of silver were prepared at furnace temperatures between 400 and 1000°C. (Ag melting point is 960.8°C.) In the temperature range below the melting point (400 to 950°C), very fine aerosols could be obtained at concentrations between 10 ng l –1 and 5 µg l –1 . Mean particle diameters ranged between about 2 nm and 6 nm. At temperatures above the melting point (sintered silver was maintained in a porcelain boat), the particle sizes increased rapidly up to over 0.1 µm (Figure 10.12). This aerosol reacts easily with gases and vapors, such as O 2 , H 2 S, Cl 2 , Br 2 , I 2 , etc. LABELING BY MEANS OF RADIOLABELED CONDENSATION NUCLEI The condensation methods described can be used to prepare aerosols of relatively small particle size; for example, those smaller than 0.5 µm in diameter. However, these methods are not convenient for labeling organic aerosols because oxygen has no usable radioisotopes, and carbon and hydrogen yield soft radiation. In such cases, preparation by means of radiolabeled condensation nuclei should be considered. A combination of two kinds of aerosol generators is useful for the preparation of liquid organic aerosols labeled by radioactive nuclei. It is composed of a furnace generator for preparing radio- active condensation nuclei, and a modified Sinclair-LaMer generator (Figure 10.13). An organic FIGURE 10.5 A longitudinal furnace for preparing inorganic condensation aerosols. 1 = boat containing porous ceramic and an inorganic substance; 2 = metal shield; 3 = ceramic and asbestos shield; 4 = reheater; 5 = adjusting screws; 6 = quartz tube; N 2 = nitrogen; T = thermometer; Va = Variac. L829/frame/ch10 Page 222 Wednesday, February 2, 2000 11:39 AM © 2000 by CRC Press LLC [...]... MINERAL AEROSOLS Fibrous mineral aerosols belong in the group of aerosols consisting of nonspherical particles The particle shape, size, and chemical composition are parameters characterizing the physical, chemical, as well as toxic effects of any fibrous aerosol. 4 2-5 1 The procedure of radioactive labeling is therefore of basic importance in physico -chemical and toxicological studies in this field The. .. shown in Table 10. 5, are present in other asbestos minerals (e.g., in amphiboles) and also in the products of man-made mineral fibers 51Cr and 59Fe are therefore the most important radio-tracers of mineral fibers The classified and radiolabeled fibrous probes are then used for aerosol generation A vibrating bed aerosol generator47 can be then used to obtain a reproducible cloud of radiolabeled fibrous aerosols... 1986, accident at the Chernobyl nuclear generating station in the Ukraine did involve very high and dangerous release of radiolabeled aerosols An explosion and fire in the reactor core dispersed radiolabeled aerosols into the nearby environment (Figure 10. 25) as well as into the global atmsophere.7 1-7 7 Chernobyl Aerosol Characterization The Chernobyl accident resulted in the discharge from the damaged reactor... 95Zr 103 Ru 106 Ru 140Ba 141Ce 144Ce 89Sr 90Sr 239Np 238Pu 239Pu 240Pu 241Pu 242Cm 133 Half-life (d) Inventory (Bq) Percentage Released 3930.0 5.27 8.05 3.25 750.0 1.1 104 2.8 65.5 39.5 368.0 12.8 32.5 284.0 53.0 1.02 104 2.35 3.15 104 8.9 106 2.4 106 800.0 164.0 Element 3.3 × 101 6 1.7 × 101 8 1.3 × 101 8 3.2 × 101 7 1.9 101 7 2.9 101 7 4.8 101 8 4.4 101 8 4.1 101 8 2.0 101 8 2.9 101 8 4.4 101 8 3.2 101 8... 11:39 AM 238 Aerosol Chemical Processes in the Environment RADIOACTIVE LABELING OF ATMOSPHERIC AEROSOLS Radioactively labeled, finely dispersed aerosols are produced in the atmosphere — partly in a natural way and partly emitted into the atmosphere from several anthropogenic sources.6 5-7 9 They represent, in some situations, a non-negligible health risk for the general population Nevertheless, they are also... activation is the principal method used for radiolabeling on mineral fibers Nevertheless, a few other techniques are also mentioned in the literature.4 8-5 1 Tewson et al have successfully used the radioisotope 68Ga, with a half-life of 68 min.48 The tracing was very effective and specific activities of about 1 µCi (37 kBq)/mg were obtained Turnok et al labeled the mineral fibers using T3O The labeling was realized... controlled The original gas mixture (B) is labeled by the 14C-benzene (Ra-B) by this procedure, and is then introduced into the burner The fine carbonaceous aerosol thus produced is labeled by 14C (Figure 10. 18) and has specific activities in the range 1 to 10 µCi (37 to 370 kBq)/mg Such a model carbonaceous aerosol can be loaded with different PAH (non-active or radioactive) and used in physico -chemical. .. acetylene and benzene The gamma-ray spectra of neutron-irradiated fibrous samples exhibit the same range of radionuclides In the Table 10. 5, the principal gamma-emitting products of neutron-irradiated chrysotile asbestos are listed The principal, relatively long-lived activation products 46Sc, 51Cr, 59Fe, and 60Co are induced in the (neutron, gamma) reaction on the corresponding stable element Similar trace... time The principle of another labeling technique is shown in the Figure 10. 22 The exposure can be carried out in a small, O-ring-sealed glass chamber that is evacuated.54,55 226Ra source is used; it emits recoil atoms of 222Rn and also recoil atoms of 218Po and 214Pb Immediately after the end of the implantation period, the activity of the implanted specimen (filter) is dominated by the activity of injected... in addition to the larger amounts of noble gases (85Kr and 133Xe) The total core inventory of the exploded unit 4 of the Chernobyl Atomic Energy Station was at the level of 100 0 MCi (3.7 101 9 Bq) before the accident.71,72 The total release of radionuclides was estimated by the International Atomic Energy Agency in Vienna in 1996 (Table 10. 9) The atmospheric transport of the released radiolabeled aerosol . Labeling in Experimental Aerosol Research 231 The gamma-ray spectra of neutron-irradiated fibrous samples exhibit the same range of radio- nuclides. In the Table 10. 5, the principal gamma-emitting. and if the air is free of aerosols, they quickly diffuse back to the surface of the tube, where they are retained. If the air contains aerosol particles, however, some of the RaA atoms are retained. atoms are retained by the aerosol; and the retention of RaA atoms increases with increasing concentration of the aerosol. An instrument for continuous measurements of inactive aerosol concentration,