Radioactivation analysis

Radioactivation analysis based on has largely replaced the earlier isotopic dilution method, and is now a well-established technique. In this technique, the unknown material and a sample containing a known concentration of the element ( P), are bombarded with neutrons under identical conditions. Each sample will thus have the same proportion of its P converted into P, and measurement of the latter in the two samples will enable the original P content of the unknown material to be estimated. Phosphorus is well suited for this kind of analysis because its half-life is long compared with the time required for activation, and the efficiency of activation from a given amount of radiation is high. The latter is usually known as a high neutron capture cross section . 

A scheme of activation analysis usually includes a chemical separation process or the addition of a carrier . It is sometimes desirable to remove chemically, before activation, any elements which would cause interference. For example, the presence of sulphur or chlorine in the sample could cause inaccuracies in the estimation of phosphorus content due to reactions (13.216) and (13.217) taking place and providing extra radioactive phosphorus. In a similar manner silicon can also cause interference with the phosphorus estimation owing to the side reaction. 

An increased sensitivity of detection can often be obtained by concentration of the total phosphorus content after irradiation bnt before measurement of the P content. In some analyses requiring the detection of very small concentrations of phosphorus, the addition, after irradiation, of a carrier material may also be incorporated in the procedure. This might he in the form of a (measured) quantity of the original P compound, since after irradiation only the P content is measured. The reason for using the carrier is that, with very low concentrations, a significant proportion of the phosphorus compound (both isotopes) may be lost in the analysis process, as, for example, by absorption on glassware. The added carrier prevents disproportionate loss of the radioactive atoms, whose concentration has to be measured. 

Radioactivation analysis is sensitive to 10 g phosphorus and the elanent can be measured in concentrations down to a few parts per million in such diverse substances as aluminium, alumina, iodine, silicon, paper, beer, oils and rocks. 

A particularly important use is in the determination of traces of P in the iodine used to make Sil4, the source of high-purity semiconductor silicon. Irradiation of the sample produces both radioactive iodine and phosphorus. The half-life of the former isotope is, however, only 25 min and after a few hours its concentration is negligible. After this period the measured radioactivity, for practical purposes, is due only to the P content and from this the P content of the original iodide sample can be measured. Using direct radioactivation, the P content of semiconductor silicon can be estimated down to 2 ppm or less. 

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Soft, silver white metal that is isolated in the tiniest of amounts. All isotopes are radioactive, the longest-lived has a half-life of 22 years. The element is an intermediate in the decay series of 235U. Strong alpha emitter that is used in radioactivation analysis and forms an effective neutron source with beryllium. 

Nuclear bombardment reactions in which the product is radioactive constitute the basis of radioactivation analysis (p. 456). Although in principle any bombardment-decay sequence may be used the analyst is largely concerned with thermal neutron activation. Equation (10.13) relates the induced activity to the amount of the parent nucleide (analyte). However, practical difficulties arise because of flux inhomogeneities. It is common therefore to irradiate a standard with very similar characteristics alongside the sample, e.g. for a silicate rock sample a standard solution would be evaporated on to a similar amount of pure silica. On the assumption that identical specific activities for the analyte are then induced in the sample and standard, the amount w2 of analyte is readily calculated from... 

Winchester, John W., Radioactivation Analysis in Inorganic Geochemistry Wink, David, see Ford, Peter C. Witt, Michael and Roseky, Herbert W., Sterically Demanding Fluorinated 2 1... 

Radioactivation analysis is used for the analysis of trace amounts of suitable elements. It is a technique that is not generally applicable to biological material although it has been used for the measurement of lead in hair and nails. 

K. Kobayashi, T. Shigematsu, Trace determination of iron, cobalt, nickel and copper in zirconium fluoride by substoichiometric radioactivation analysis, J. Radioanal. Nucl. Chem. Articles 113 (1987) 333-341. 

Activation (or radioactivation) analysis 1 A99— A100 see Radiation gauging in energetic matls 9 R76-R103, also Radioactive tracers 9 R104-R113... 

Radioactivation analysis has been used to measure bromine in polymers (37—39) and recently a novel technique for trace oxygen has been reported (40). Any polymer or other material (e.g. metal alkyl) which is miscible with butyl lithium solutions may be analysed since the procedure involves the intermediate production of triton particles by the nuclear reaction 6Li (n, a) t. The tritons then act as nuclear projectiles for the activation of oxygen 0 (t, n) 18F and the radioactivity due to fluorine-18 is measured. A sensitivity of 1 x 10 g in a 0.5 g sample is claimed. 

There is a wide range of applications for methods of analysis that are based upon the energies and intensities of the radiations emitted by radioactive nuclides. These techniques sometimes are temied radiometric methods of analysis. The methods are not restricted to the determination of substances initially radioactive, since there is wide use of methods involving the irradiation of stable, nuclides to produce radioactive ones, followed by measurement of their radiations, horn which the composition of the original stable substance can be inferred This method is radioactivation analysis. Another method for the use of measurements of radioactivity in the analysis of stable substances is that of tracer techniques, that is, by the addition to them of radioactive nuclides, which can then be used to follow the course of various reactions or processes. There are various ways of introducing the radioactive nuclides, which are discussed later in this entry. 

Radioactivation Analysis. The principle of this technique is that a stable isorope when irradiated by neurrons, by charged particles such as protons or deuterons or by gamma rays, can undergo a nuclear reaction to produce a radioactive nuclide. After the radionuclide is formed, and its radiations have been characterized by radiation detection devices, calculations can be made of the elements contained in the sample before irradiation. 

Radioactivation Analysis. See Activation Analysis A99-L RATO. See under ATO A497-R Ripping Ammonal A289 (table)... 

Payne, B. R. Radioactivation Analysis Symposium, Vienna, 1959. Radioactivation Analysis Proceedings. London Butterworth 1960. 

Bowen, H. I, M., and D. Gibbons Radioactivation Analysis. Oxford Clarendon Press 1963. 

Winchester, John W., Radioactivation Analysis in Inorganic Geochemistry. . 2 1... 

International Atomic Energy Agency Joint Commission on Applied Radioactivity (I. C. S. U.) Radioactivation Analysis-Proceedings of the Radioactivation Analysis Symposium held in Vienna, Austria, June 1959. London Butter-worth 1960. 

Trace metals in sufficient quantities to initiate autoxidation occur not only in crude hydrocarbons, fats, and oils, but also in highly purified materials—e.g., highly purified linoleic acid was found to contain 0.21 p.p.m. Cu and 0.0008 p.p.m. Co (results obtained by radioactivation analysis). 

The operation, since 1945, of nuclear reactors has made available radioisotopes of most elements. The isotopes are useful in a variety of chemical investigations, including those concerned with solubility, diffusion, reaction mechanism and structure. They have given rise to new analytical techniques, such as isotopic dilution and radioactivation analysis. In industry also, they have a wide and rapidly expanding application. All this is made possible by the ease with which small quantities of the nuclides can be detected, often remotely, and quantitatively determined by commercially available and easily operated equipment. 

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