Radioactive elements as tracers

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. 

This review is concerned principally with the use of the rare earth elements as tracers of geological processes. We do not discuss, except in passing, the great advances which have resulted from the use in geochemistry and cosmochemistry of the radioactive decay of to Nd and Lu to " Hf. These topics each... 

A valuable technique for research is the use of both radioactive and non-radioactive isotopes as tracers. By the use of these isotopes an element can be observed in the presence of large quantities of the same element. 

The first ever application of a radiotracer in a biological experiment dates back to 1923 when George de Hevesy used Pb to study plant uptake of lead from solution [5]. His seminal work was honored by the Nobel Prize in Chemistry in 1943 and made him the father of isotope tracing, a tool that is still indispensable in virtually any area of scientific research. The first use of a stable isotope to study mineral metabolism was reported in 1963, when Lowman and Krivit injected stable Fe together with radioactive Fe into a human subject to compare the plasma clearance of the two isotopes [6]. However, it was not until the 1980s that stable isotope techniques were explored systematically to study mineral and trace element metabolism in humans. This was not only due to the increasing recognition of health hazards associated with the use of radioisotopes. Mass spectro-metric techniques had to be refined to measure isotope ratios of the heavier elements at a precision suitable for the exploitation of isotopically enriched elements as tracers. Stable isotopic labels are made up from the same isotopes as the natural element, from which they differ only in terms of composition, that is, in the relative abundances of their isotopes. 

Other radioisotopes known to be produced by cosmic rays include Be, H, Na, Be, and Of these Be, P, and P have activities that are high enough to be measured in rainwater. In several instances, notably 0 and Be, these radioactive elements are useful as tracers. 

The role of radionuclides as tracer of the chemical transport in river is also reinforced by the fact that each of the U-Th-Ra elements has several isotopes of very different half-lives belonging to the U-Th radioactive series. Thus, these series permit comparison of the behavior of isotopes of the same element which are supposed to have the same chemical properties, but very different lifetimes. These comparisons should be very helpful in constraining time scales of transport in rivers. This was illustrated by Porcelli et al. (2001) who compared ( " Th/ U) and ( °Th/ U) ratios in Kalix river waters and estimated a transit time for Th of 15 10 days in this watershed. The development of such studies in the future should lead to an important progress in understanding and quantifying of transport parameters in surface waters. This information could be crucial for a correct use of U-series radioactive disequilibria measured in river waters to establish weathering budgets at the scale of a watershed. 

The origin of Aeolian dust from Chinese desert to Japanese islands was studied with ESR of dust, mostly fine grains of quartz.132 Suspended particulate matter (SPM) collected by environmental protection agency was measured with ESR.133 Dust soot of automobiles was also measured to check the motor combustion rate. Adsorption of NO, Mn2+ and Gd3 on clay minerals, bentonite and se-piolite134 has been studied using paramagnetic ions as tracers for radioactive elements. And studies have been carried out on how divalent and trivalent cations diffuse and blocked by surrounding clay minerals, in the context of their leak from nuclear waste repository to the environment.135... 

HEVESY, GEORG de (1885-1966). A Hungarian chemist who won the Nobel prize in chemistry in 1943, for his work on (he use of isotopes as tracers in the study of chemical processes. He discovered the element hafnium in 192.7. One of his interesting projects involved the calculation of ihc percentages of chemical elements in the universe. He also was involved in research using radioactive lead and phosphorus traces. His work included the separation of isotopes by physical means. His Ph D was granted ai Freiburg in 1908. 

Use of stable isotope dilution to assay elemental concentrations in biological samples has increased markedly in the recent past. Part of the reason is that use of radioactive isotopes previously employed as tracers has declined, and part is that interest in the effect of various elements on biological systems and their fate once they enter the food chain has increased. This important field is far from the author s area of expertise, so what follows should be considered a rather haphazard survey... 

A radioactive isotope (radioisotope) is an unstable isotope of an element that decays into a more stable isotope of the same element. They are of great use in medicine as tracers (to help monitor particular atoms in chemical and biological reactions) for the purpose of diagnosis (such as imaging) and treatment. Iodine (-131 and -123) and Technetium-99 are used for their short half-lives. 

Radioactive isotopes have the same chemical properties as the nonradioactive isotopes of the same element. Because they undergo the same chemical reactions, radioactive atoms are often used as tracers to determine what ordinary atoms are doing. For example, to detect problems in the human thyroid gland, physicians often presCTibe iodine that includes a tiny fraction of 53 , a radioactive isotope of iodine. The body should utilize all the iodine in the thyroid gland. With a Geiger counter, the physician can follow the path of the radioactive isotope. If the radioactive iodine is not absorbed by the thyroid, then the regular iodine has not been absorbed either, and the physician has confirmed that a certain problem exists. 

An extremely valuable technique for research that has been developed in recent years is the use of both radioactive and nonradioactive isotopes as. tracers. By the use of these isotopes an element can be observed in the presence of large quantities of the same element. For example, one of the earliest uses of tracers was the experimental determination of the rate at which lead atoms move around through a crystalline sample of the metal lead. This phenomenon is called self-diffusion. If some radioactive lead is placed as a surface layer on a sheet of lead, and the sample is allowed to stand for a while, it can then be cut up into thin sections parallel to the original surface layer, and the radioactivity present in each section can be measured. The presence of radioactivity in layers other than the original surface layer shows that lead atoms from the surface layer have diffused through the metal. 

Almost all elements found in nature can now be made radioactive. Radioactive potassium and phosphorus are used as tracers to measure how effectively plants take up fertilizer from soil. Radioactive iodine is applied in nuclear medicine to diagnose and treat thyroid problems. Radiation treatment for cancer therapy uses radioactive cobalt, which is made by irradiating ordinary cobalt with neutrons. 

Arsenobetaine, arsenosugars and arsenocholine are organoarsenicals less toxic for animals and humans than inorganic arsenic compounds, and have been found in certain marine organisms and in seafoods. They are excreted rapidly in urine (about 70% of the dose in 24h) . Natural arsenic is a pure one-isotope element ( As) and had to be labelled with radioactive arsenic for metabolic studies. As has been chosen as the most suitable isotope for tracer investigations. 

In medical installations, the use of radioactive isotopes for diagnosis and therapy has significantly increased in the past years. Nonencapsulated radioactive elements are used for different purposes such as in diagnosis by tracers, treatment of thyroid or blood disorder, and in medical research. These activities produce some solid radioactive wastes like cotton, rubber gloves, syringes, etc., as well as liquid wastes, mainly scintillation liquids. Another type of waste is the encapsulated sources that are used for cancer treatment these elements must be changed when their activity decays below a certain level. 

Radioactive isotopes are often used as tracers to follow the path of an element through a chemical reaction. For example, using radiotracers chemists have determined that the oxygen atoms in O2 that are produced by a green plant during photosynthesis come from the oxygen in water and not the oxygen in carbon dioxide. 

One application of radioactive tracer techniques of considerable importance in solid state structural problems is the emanation method due to Hahn (21). The method has been employed widely and has been developed recently as a sensitive, quantitative method by Gregory (22), who has employed it for the investigation of structural changes and for the extraction of diffusion data. The procedure in outline is as follows A convenient amount of a radioactive element which decays to an isotope of radon (e.g., radiothorium) is ccprecipitated... 

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