Activation analysis principles

H. J. M. Bowen, in Activation Analysis, Principles and Applications, Academic Press, New York, 1965, pp. 143-148. 

Principles and Characteristics In neutron activation analysis (NAA) the sample is irradiated by neutrons. The principal reaction in NAA is ... 

Activation analysis is based on a principle different from that of other analytical techniques, and is subject to other types of systematic error. Although other analytical techniques can compete with NAA in terms of sensitivity, selectivity, and multi-element capability, its potential for blank-free, matrix-independent multielement determination makes it an excellent reference technique. NAA has been used for validation of XRF and TXRF. 

Introduction to nuclear structure and the principles of neutron activation analysis... 

UV/Vis-spectroscopy is the classical method of analysis of enzyme activity. The principle is the change in absorption behavior of a substrate during the reaction process, for example by modification or Hberation of a chromophoric function. A number of enzymes from different classes can be assayed spectrophoto-metrically using their natural substrates or cofactors. In this way, activity of acetyltransferases can be estimated by measurement of absorption of acetyl coenzyme A at 232 nm [33]. Oxidoreductases which require a cofactor, e.g., NAD/NADH, to carry out the transfer of hydrogen can be characterized by measuring the absorption of this cofactor depending on its oxidation stage [33]. 

Kruger, P. Principles of Activation Analysis, Wiley, New York, 1971. 

Uranium in nature may be measured either radiometrically or chemically because the main isotope - 238U - has a very long half life (i.e., relatively few of its radioactive atoms decay in a year). Its isotopes in water and urine samples usually are at low concentrations, for which popular analytical methods are (1) radiochemical purification plus alpha-particle spectral analysis, (2) neutron activation analysis, (3) fluorimetry, and (4) mass spectrometry. The radiochemical analysis method is similar in principle to that of the measurement of plutonium isotopes in water samples (Experiments 15 and 16). Mass spectrometric measurement involves ionization of the individual atoms of the uranium analyte, separation of the ions by isotopic mass, and measurement of the number of separated isotopic ions (see Chapter 17 of Radioanalytical Chemistry text). 

In many laboratories that have access to a nuclear reactor, neutron activation is used for the chemical analysis of rocks, minerals, petroleum, biological tissues, alloys, etc., and the technique is well suited for the determination of the concentrations of trace elements in polymers. Neutron activation analysis was used by Given et al. (1) in their studies of water tree growth in polymeric insulation and by Wu and Chen (2) in their studies of dopant-polymer interactions in MoCl5-dcped polyacetylene films. In this work the principles of the method are described and the possibilities are illustrated by means of measurements carried out on polyethylene. 

Two radioanalytical methods described in chapter 17 are applied preferentially in the life sciences, activation analysis and isotope dilution, the latter mainly in combination with the substoichiometric principle. 

In principle, radiometric techniques are most suitable for the shorter-lived radio-nuclides, whereas at longer half-lives (-100 years or more) techniques based on mass spectrometry or neutron activation analysis start to become more sensitive. This is shown in Table 12.10. 

Antimony can be readily determined in petroleum at a concentration of less than 10 ng/g by instrumental neutron activation analysis with a 1-hr irradiation at a neutron flux of 1012 n cm"2 sec"1. The principle radiation arising from the 121Sb (n, y) 122Sb activation and subsequent decay of 122Sb occurs at 564 KeV. With a high resolution Ge(Li) detector antimony may be measured in the presence of 82Br (550 KeV) and 76As (559 KeV), which may be found in some petroleum matrices. 

Arsenic levels below 10 ng/g can be readily detected in petroleum by instrumental neutron activation analysis. The most convenient technique involves direct gamma counting based on the 75As (n, y) 76As reaction with a principle radiation of 559 keV. After a 1-hr irradiation at a neutron flux of 1012 n cm"2 sec-1, the arsenic may be counted in a relatively short time. The method requires a high resolution Ge(Li) detector to avoid interference from bromine (550 keV) or antimony (564 keV). 

Earlier methods used to determine mercury in biological tissue and fluids were mainly colorimetric, using dithizone as the com-plexing agent. However, during the past two to three decades, AAS methods - predominantly the cold vapor principle with atomic absorption or atomic fluorescence detection - have become widely used due to their simplicity, sensitivity, and relatively low price. Neutron activation analysis (NAA), either in the instrumental or radiochemical mode, is still frequently used where nuclear reactors are available. Inductively coupled plasma mass spectrometry (ICP-MS) has become a valuable tool in mercury speciation. Gas and liquid chromatography, coupled with various detectors have also gained much importance for separa-tion/detection of mercury compounds (Table 17.1). 

X-ray fluorescence spectrometry, gas chromatography and neutron activation analysis (NAA). An older book edited by Hofstader, Milner and Runnels on Analysis of Petroleum for Trace Metals (1976), includes one chapter each on principles of trace analysis and techniques of trace analysis and others devoted to specific elements in petroleum products. Markert (1996) presents a fresh approach to sampling, sample preparation, instrumental analysis, data handling and interpretation. The Handbook on Metals in Clinical and Analytical Chemistry, edited by Seiler,... 

The following books provide in-depth coverage or include a discussion of the principles and techniques of activation analysis. The 532-page book by Ehmann and Vance... 

The fundamental principle behind analysis by activation analysis is activation or excitation of an atomic nucleus by exposure to radiation such as neutrons, protons or high-energy photons with subsequent measurement of emitted sub-atomic particles or radiation. The most common aspect of the technique involves activation with neutrons in a nuclear reactor and measurement of delayed emitted gamma rays, denoted neutron activation analysis, either instrumental neutron activation analysis (INAA) or neutron activation followed by radiochemical separation (RNAA) in which the element of interest is chemically separated from the matrix after irradiation to provide for better, unimpeded counting. 

Excellent, comprehensive treatments of the principles and fundamentals of nuclear activation analysis - including applications fundamentals - are found in the following five consecutive chapters in the first edition of Treatise on Analytical Chemistry Finston (1971a) (Radioactive and isotopic methods of analysis nature, scope, limitations, and interrelations) Finston (1971b) (Nuclear radiations characteristics and detection) Crouthamel and Heinrich (1971) (Radiochemical separations) Seaman (1971) (Tracer techniques) and Guinn (1971) (Activation analysis). A series of seven similarly comprehensive chapters appeared in the updated second edition Lieser (1986), (Fundamentals of nuclear activation and radioisotopic methods of analysis) Herpers... 

The history of neutron activation analysis goes back to the middle of the 1930s when it was first described by G. Hevesy and H. Levi at the Niels Bohr Institute in Copenhagen. The principle of the technique is that elements can be made radioactive by exposure to neutron irradiation. Two types of physiological processes are associated with this activation one prompt and one delayed. Classically, neutron activation analysis is based on the detection of the delayed event, viz. the characteristic radiation emitted during the decay -with a specific half-life (ti/a) - of the unstable nuclei formed by (n,y) reaction. 

Neutron activation analysis is an invaluable technique for trace element determinations in biological matrices. Probabiy its most important advantage is its relative freedom from errors due to extraneous additions of exogenous materiai from reagents, equipment, or laboratory environment. Characteristics which contribute further to the popularity of the technique are its outstanding sensitivity, excellent specificity, and multielement capability. In principle, the technique is able to produce relatively unbiased and precise measurements — at least in competent hands. That it is, however, necessary to warn against uncritical expectations is illustrated by the grossly inconsistent results obtained in several laboratories. 

Kruger, P. "Principles of Activation Analysis Wiley-Interscience New York, 1971 pp. 482-503. 

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