Tracer artificial

Cobalt-60, an artificial isotope, is an important gamma ray source, and is extensively used as a tracer and a radiotherapeutic agent. 

Following the movement of airborne pollutants requires a natural or artificial tracer (a species specific to the source of the airborne pollutants) that can be experimentally measured at sites distant from the source. Limitations placed on the tracer, therefore, governed the design of the experimental procedure. These limitations included cost, the need to detect small quantities of the tracer, and the absence of the tracer from other natural sources. In addition, aerosols are emitted from high-temperature combustion sources that produce an abundance of very reactive species. The tracer, therefore, had to be both thermally and chemically stable. On the basis of these criteria, rare earth isotopes, such as those of Nd, were selected as tracers. The choice of tracer, in turn, dictated the analytical method (thermal ionization mass spectrometry, or TIMS) for measuring the isotopic abundances of... 

In the marine environment, the numerous radionuclides can be classified into three broad categories based on their production or origin (1) those derived from the weathering of continental rocks, the primordial radionuclides, (2) those formed from cosmic radiation, the cosmogenic radionuclides, and (3) those artificially introduced into nature, the anthropogenic or transient radionuclides and tracers. The primordial radionuclides (e.g. Th, and U) were... 

In the Type III pile, an apparent wetting front created by several artificial rainfall events conducted in late 2006 led to an elevated zone of moisture in the upper 3 m of the pile. Rainfall events late in the summer 2007, linked to two tracer tests, resulted in a wetting front that penetrated to a depth of approximately 8 m. This moisture was subsequently mobilized through the summer 2008 season as the pile warmed above 0°C (Neuner et al. 2009). 

In addition, artificial materials have been employed in diverse diagnostic and therapeutic applications and biotechnologies, e.g., tracers for advanced imaging technologies, carriers for controlled drug and gene delivery, biosensors and growth supports for cells in a culture. 

The isotope iodine-131 is an artificial radioisotope of iodine used as a tracer in biomedical research and as a treatment for thyroid disease. 1-131 has a half-hfe of about eight days, which means it will be eliminated from the body in several weeks. 

Ammonium thiocyanate is used in the manufacture of herbicides, thiourea, and transparent artificial resins in matches as a stabilizing agent in photography in various rustproofing compositions as an adjuvant in textile dyeing and printing as a tracer in oil fields in the separation of hafnium from zirconium, and in titrimetric analyses. 

Overall, serum and urinary increment methods have shown that a Ca source (e.g., CaCOs) accompanied by citrate is better absorbed than one that is not (Heaney et ah, 1999). Citrate that is absorbed into circulation is inclined to bind Ca ions and thereby artificially elevate incremental data compared to other salts (Heaney, 2001b). A number of studies utilizing the most sensitive isotopic tracer methods have demonstrated that CCM is highly absorbable compared to other Ca sources (Abrams et ah, 2003 Heaney et ah, 1989b Miller et ah, 1988 Smith et ah, 1987). 

Composizioni (o Miscele) per traccianti (Tracer Compositions). See under PIROTECNIA o ARTIFICI DA GUERRA... 

Isotope ratio measurements are performed whenever the exact ratio, or abundance, of two or more isotopes of an element must be known. For example, the isotopic ratios of lead are known to vary around the world, so it is possible to determine the source of lead in paint, bullets and petrol by knowing the isotopic abundances of the four lead isotopes 204, 206, 207, 208. Another example is the use of stable isotopes as metabolic tracers, where an animal is both fed and injected with an element having artificially enriched isotopes and the fractional absorption of the element can be accurately determined. 

Peeters et al. (1996) have made a series of experiments with artificial tracers added to the upper hypolimnion of several Swiss lakes or basins of lakes (basin size between 5 and 220 km2). They always found elongated cloud shapes which they approximated by ellipses. The principal axes grew with time as ... 

The use of isotopes in mechanistic and analytical chemistry has been known since about 1913 but it was the advent of artificially produced isotopes in the period from 1945 onwards that really marked the beginning of a wide range of isotopic tracer techniques. There is now an extensive literature on tracer techniques and a few of the more useful references are included at the end (7—5). 

Revs 27,199-285( 1940) (ca 600 refs)( Artificial radioactivity) 6)G.vonHevesy, "Radio active Indicators, Interscience, NY(1948) 7)G.K.Schweitzer, "Radioactive Tracer Techniques, Van No strand, MY(1949) 8)... 

From the above it can be concluded that in many instances the introduction of an artificial radionuclide into the environment provides us with a natural tracer experiment. Indeed, this is the basis for the application of deterministic compartmental models, based on tracer kinetics, to radioecology (Whicker and Schultz, 1982). This approach is largely based on the assumption that radionuclide movements will exhibit first order kinetics although the existence of naturally-occurring tracees (stable isotopes) at relatively high abundance may result in more complex concentration-dependent kinetics. Furthermore, nutrient analogues may exert even more complex effects on processes such as radioion absorption across root plasma membranes this will become evident later in the chapter. 

The ApBq and A Bn layers are seen to grow parabolically, whereas the thickness of the ArBs layer will gradually decrease with passing time. Eventually, this layer will disappear. It is easy to notice that in this case the values of the diffusional constants k[A2 and kim can readily be determined from the experimental dependences x2- t and z2- t, respectively, using an artificially prepared specimen A-ApBq-ArBs-A iB,-B or A-A,B-B. It is essential to mention that both the ApBq and AtBn layers must be the first to occur at the A-B interface. The diffusional constant k[A2 thus obtained is the reaction-diffusion coefficient of the A atoms in the ApBq lattice, while the diffusional constant klB3 is the reaction-diffusion coefficient of the B atoms in the Afin lattice, to be compared with respective self-diffusion coefficients determined using radioactive tracers. 

Two alternative approaches exist. The first one involves significantly lowering the temperature to values where the diffusion of vacancies can be observed with a technique like STM. At lower temperatures a surface vacancy can then be artificially created by ion bombardment or direct removal of an atom by the tip. This approach has been applied successfully to several semiconductor surfaces [29-31]. For metal surfaces, although vacancy creation at a step by direct tip manipulation of the surface has been demonstrated [32], to our knowledge, no studies have been published where the diffusion of artificially created vacancies in a terrace has successfully been measured. The second approach involves the addition of small amounts of appropriate impurities that serve as tracer atoms in the first layer of the surface [20-24]. The presence and passage of a surface vacancy is indirectly revealed by the motion of these embedded atoms. If one seeks to measure both the formation energy and the diffusion barrier of surface vacancies explicitly, a combination of these two approaches is needed. 

Chrysikopoulos CV (1993) Artificial tracers for geothermal reservoir studies. Environ Geology 22 60-70... 

For systems not artificially enriched in (e.g., tracer experiments), the discrimination factor is essentially equal to the difference between the of the substrate... 

Nuclear chemistry (radiochemistry) has now become a large and very important branch of science. Over four hundred radioactive isotopes have been made in the laboratory, whereas only about three hundred stable isotopes have been detected in nature. Three elements —technetium (43), astatine (85), and promethium (61), as well as some trans-uranium elements, seem not to occur in nature, and are available only as products of artificial transmutation. The use of radioactive isotopes as tracers has become a valuable technique in scientific and medical research. The controlled release of nuclear energy promises to lead us into a new world, in which the achievement of man is no longer limited by the supply of energy available to him. 

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