Tracers, production

Abstract Methods for the synthesis of compounds labeled with the short-lived positron emitting radionuclide are described. Important aspects on how to achieve high specific radioactivity and the need for technical solutions to establish a reproducible routine tracer production are pointed out. Examples of positron emission tomography (PET) as a tool in drug development are also included. 

Remote or processor-controlled automated device. Remote or processor-controlled automated devices, mainly developed for radiation protection purposes, also have other advantages such as increasing the reproducibility in the tracer production. This also facilitates... 

The requirement for a rapid tracer production means that the synthesis should be designed in such a way that the C atom is introduced as late as possible. This approach is exemplified by alkylation of carbon, nitrogen, oxygen, and sulfur nucleophiles with [ C]methyl iodide, a synthetic route that provides a general method for the labeling of many biomedically interesting compounds. 

Polymer retention was determined by material-balance calculations in which the area under each polymer production curve was compared with the area represented by the injected polymer slug. An alternative method to determine polymer retention was based on the areas of the polymer and tracer production curves. 

Recent developments in the production of neutron sources have led to the rejection of °Po-Be sources in favour of the more convenient Cm-Be source. The half-life of the latter source (163 d) being comparable with that of °Po (138 d). A recently designed Sb-Be source provides a thermal-neutron flux of 10 n" s over an irradiation volume of 20 cm . This is at the centre of a large Be moderator block containing holes for the insertion of Sb pencils. The course has been designed specifically for activation analysis and short-lived tracer production. 

The use of tracers enables efficient and reliable measurements of oil, gas and water flow in industrial process units and pipe line systems under production conditions thus fundamentally being non-destructive testing methods. Typical problems which can be efficiently assessed by tracer studies include ... 

In situ control and calibration of flare and other gas metering systems is performed by gaseous tracers using the transit time method without affecting the normal production. Details about methodology are given in / /. 

Deuterium is used as a moderator to slow down neutrons. Tritium atoms are also present but in much smaller proportions. Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen (fusion) bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer. 

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

The changeover from ROO radicals to HOO radicals and the switch from organic peroxides to HOOH has been shown as temperature is increased in propane VPO (87,141). Tracer experiments have been used to explore product sequences in propane VPO (142—145). Propylene oxide comes exclusively from propylene. Ethylene, acetaldehyde, formaldehyde, methanol, carbon monoxide, and carbon dioxide come from both propane and propylene. Ethanol comes exclusively from propane. 

The use of radioactive tracers was pioneered by Georg von Hevesy, a Hungarian physical chemist, who received the Nobel Prize in 1943 for his work on radioactive indicators (1). Radioisotopes have become indispensable components of most medical and life science research strategies, and in addition the technology is the basis for numerous industries focused on the production and detection of radioactive tracers. Thousands of radioactive tracers have been synthesized and are commercially available. These are used worldwide in tens of thousands of research laboratories. 

Many applications ia tracer technology require products of high specific activity, ie, compounds having a high degree of substitution of specific atoms with radioisotopes. For many labeled compounds nearly 100% labeling can be achieved at one or more locations ia a molecule usiag... 

The small synthetic scale used for production of many labeled compounds creates special challenges for product purification. Eirst, because of the need for use of micro or semimicro synthetic procedures, the yield of many labeled products such as high specific activity tritiated compounds is often low. In addition, under such conditions, side reactions can generate the buildup of impurities, many of which have chemical and physical properties similar to the product of interest. Also, losses are often encountered in simply handling the small amounts of materials in a synthetic mixture. As a consequence of these considerations, along with the variety of tracer chemicals of interest, numerous separation techniques are used in purifying labeled compounds. 

Decay products of the principal radionuclides used in tracer technology (see Table 1) are not themselves radioactive. Therefore, the primary decomposition events of isotopes in molecules labeled with only one radionuclide / molecule result in unlabeled impurities at a rate proportional to the half-life of the isotope. Eor and H, impurities arising from the decay process are in relatively small amounts. Eor the shorter half-life isotopes the relative amounts of these impurities caused by primary decomposition are larger, but usually not problematic because they are not radioactive and do not interfere with the application of the tracer compounds. Eor multilabeled tritiated compounds the rate of accumulation of labeled impurities owing to tritium decay can be significant. This increases with the number of radioactive atoms per molecule. 

Radioactive tracers account for about 20% of the worldwide market for consumables and reagents for life science research. In 1994 the value was estimated at about 300 million. The principal fuU line manufacturers are Du Pont—NEN Research Products (Boston, Massachusetts) and Amersham International (Amersham, U.K.). These companies share roughly equaHy about 85% of the radiochemicals worldwide market. In addition to an extensive line of catalog products, these suppHers offer custom labeling and custom synthesis services. The rest of the market is shared by producers of a limited range of products or services, such as ICN Biomedicals (Costa Mesa, California) and American Radiolabeled Chemicals (St. Louis, Missouri). 

Yearly consumption of isotopes for production of tracer chemicals varies depending on the radionucHde. Eor example, about 1,100 GBq (30 Ci) of P was expected to be utilized worldwide in 1995 compared with ca 7,400 TBq (200,000 Ci) of tritium. 

Concerns over safe handling of radioactive materials and issues around the cost and disposal of low level radioactive waste has stimulated the development of nonradiometric products and technologies with the aim of replacing radioactive tracers in research and medical diagnosis (25). However, for many of the appHcations described, radioactive tracer technology is expected to continue to be widely used because of its sensitivity and specificity when compared with colorimetric, fluorescent, or chemiluminescent detection methods. 

Hot atom reactions have also been used to label organic compounds with T. Irradiation of helium-3 with neutrons according to the nuclear reaction produces very energetic tritium atoms that can displace ordinary hydrogen in organic compounds. This procedure is not very selective, and the labeling pattern must be determined to enable the tritiated product to be used effectively as a tracer (34). 

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... 

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