Neutron activation procedure

The properties of such materials are not measurably altered until subjected to doses in excess of a million rads. At these higher doses, the principal changes are due to chem decompn which, with very few exceptions, resnlt in a decrease in sensitivity to mechanical stimulus and also in a dimunition of expl output. The radiation doses normally encountered in neutron activation procedures range from a few rads for 14 MeV fast neutron activation to several thousand rads for thermal neutron activations in a nuclear reactor. Thus, such doses are well under the limit at which measurable changes can occur... 

These techniques are designed to minimize both the actual working time, required and the analytical uncertainties in sample analysis. Sample preparation and neutron activation procedures are based on proved analytical and microanalytical techniques. The unusually high sensitivity, reliability, and accuracy are achieved through a choice of optimum irradiation and counting times for the y-ray detection systems. 

This analytical method measures two elements, K and Th, which were also determined via NAA. However, the neutron activation procedure is limited to samples weighing a few hundred milligrams. Thus, another set of internal standards was included in the analysis to insure not only consistent and accurate results, but also homogeneous samples for these elements over a sample size range of 1000-fold. 

Coincidence techniques have also been used for Compton interference reduction in the use of large volume Ge(Li) detectors together with plastic scintillator anticoincidence shields 70), In some cases it might be desirable to use the coincidence electronics to gate the multichannel analyzer to accept only non-coincident pulses. In 14 MeV neutron activation procedures the annihilation radiation resulting from the decay of 13N produced indirectly from the carbon in the plastic irradiation unit may be discriminated against by gating the analyzer to accept only non-coincident events. 

With the neutron activation procedure, the measurement of P is reliable only when there is very little Al (<20 ppm), or when an epithermal irradiation (Cd-covered) is used to correct for the direct activation of 28Al from the Al. For badly contaminated samples, the X-ray fluorescence data are more suitable for the P determination. The sequential irradiation procedures (with and without cadmium) showed that many of the mummy samples were contaminated to some extent and contained more than 20 ppm of Al. 

Analysis of Particles by Neutron Activation Analysis. The analytical neutron activation procedure used for the collected particles involved two irradiations of each filter (short-and long-term) using the standard procedures. The standards for neutron activation analysis were made with aliquots of known standards (1.000 ppt Fisher Scientific Standards) in sealed tubes. These standards were always counted with the samples. The following were the standards used in this study Na and Cl Cu and Mn Al, V, and Ti K and Br Zn and Hg Co and Cr As and Ag Se, Sc, Sb, and La and Fe, Mg, and I. 

Trace metal concentrations in seawater are so low that contamination of the sample and loss of metal to container walls are critical problems in any analytical technique. These problems are particularly severe when the water sample must undergo extensive chemical treatment prior to the determination step. Most available techniques require such a chemical step or steps, because of their inadequate sensitivity and/or inability to determine the metal in the presence of the other sea water salts. Even those neutron activation procedures established for analysis of elements in seawater usually require a preactivation concentration step (2). 

Our modern understanding of their geochemical behaviour dates from about 1960, following the introduction of sensitive and accurate radiochemical neutron activation procedures. Some of the earliest work validated the distinctive patterns of both the sediments and the meteorites (although the absolute levels measured were much lower than the earlier estimates). This led to the realisation among geochemists that the lanthanides were indeed widely fractionated under common geological conditions of temperature and pressure, and so opened up broad perspectives for research. 

The earliest methods for tin analysis, namely, gravimetric and titrimetric methods, are now mainly of historical interest. Being essentially macro methods, laborious in application, they are limited and mainly useful for levels of tin in food in the 50-100 ppm range or above. The use of colorimetric analysis is associated with problems of specificity, sensitivity, and stability of the tin complexes formed. Nowadays, methods for tin analysis in biological media include the various atomic spectroscopic techniques (atomic absorption spectrometry, atomic emission spectroscopy, and inductively coupled plasma atomic emission spectrometry) as well as electrochemical and neutron activation procedures. 

For the deterrnination of trace amounts of bismuth, atomic absorption spectrometry is probably the most sensitive method. A procedure involving the generation of bismuthine by the use of sodium borohydride followed by flameless atomic absorption spectrometry has been described (6). The sensitivity of this method is given as 10 pg/0.0044M, where M is an absorbance unit the precision is 6.7% for 25 pg of bismuth. The low neutron cross section of bismuth virtually rules out any deterrnination of bismuth based on neutron absorption or neutron activation. 

Radioactive nuclei are used extensively in chemical analysis. One technique of particular importance is neutron activation analysis. This procedure depends on the phenomenon of induced radioactivity. A sample is bombarded by neutrons, bringing about such reactions as... 

Although sophisticated methods may constitute the core methods for certification it is useful to include good, well executed routine methods. In order to further minimize systematic error, a conscious purposeful attempt should be made to get methods and procedures with wide-ranging and different sample preparation steps, including no decomposition as in instrumental neutron activation analysis and particle induced X-ray emission spectrometry. 

Domow et al. [201] have reported on the use of cyclotron-produced carrier-free and they obtained a narrower line width (53 pm s ) as compared to the procedure using neutron-activated activity. However, both procedures are... 

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

Although the neutron activation analysis is inherently more sensitive than the atomic absorption spectrometry, both procedures yield a reliable measurement of vanadium in seawater at the natural levels of concentration. 

All items of equipment must be considered, including balances and volumetric measuring devices, not just the expensive equipment. In terms of instrumentation, while a method using a mass spectrometer may be ideal for the study, if no such equipment is available the job will have to be contracted out to another laboratory, or another approach agreed with the customer. Neutron activation or radiochemical measurements require special equipment and dedicated laboratory facilities and safety procedures. Such techniques are often not generally available and are better left to specialist laboratories. 

The need for special facilities for work involving neutron activation analysis and radiochemical measurements has been referred to above in Section 4.3.6. Other safety factors may also influence your choice of method. For example, you may wish to avoid the use of methods which require toxic solvents, such as benzene and certain chlorinated hydrocarbons, or toxic reagents, such as potassium cyanide, if alternative procedures are available. Where Statutory Methods have to be used, there may be no alternative. In such cases, it is essential that staff are fully aware of the hazards involved and are properly supervised. Whatever method is used, the appropriate safety assessment must be carried out before the work is started. Procedures should be in place to ensure that the required safety protocols are followed and that everyone is aware of legislative requirements. 

Nixon277 compared atomic absorption spectroscopy, flame photometry, mass spectroscopy, and neutron activation analysis as methods for the determination of some 21 trace elements (<100 ppm) in hard dental tissue and dental plaque silver, aluminum, arsenic, gold, barium, chromium, copper, fluoride, iron, lithium, manganese, molybdenum, nickel, lead, rubidium, antimony, selenium, tin, strontium, vanadium, and zinc. Brunelle 278) also described procedures for the determination of about 20 elements in soil using a combination of atomic absorption spectroscopy and neutron activation analysis. 

Hughes, M.J., Cowell, M.R. and Hook, D.R. (1991b). NAA procedure at the BM Research Laboratory. In Neutron Activation and Plasma Emission Spectrometric Analysis in Archaeology, ed. Hughes, M.J., Cowell, M.R. and Hook, D.R., British Museum Occasional Paper 82, London, pp. 29 16. 

An introductory manual that explains the basic concepts of chemistry behind scientific analytical techniques and that reviews their application to archaeology. It explains key terminology, outlines the procedures to be followed in order to produce good data, and describes the function of the basic instrumentation required to carry out those procedures. The manual contains chapters on the basic chemistry and physics necessary to understand the techniques used in analytical chemistry, with more detailed chapters on atomic absorption, inductively coupled plasma emission spectroscopy, neutron activation analysis, X-ray fluorescence, electron microscopy, infrared and Raman spectroscopy, and mass spectrometry. Each chapter describes the operation of the instruments, some hints on the practicalities, and a review of the application of the technique to archaeology, including some case studies. With guides to further reading on the topic, it is an essential tool for practitioners, researchers, and advanced students alike. 

Trace amounts of Tc are also determined in filter paper and vegetable samples by neutron activation analysis The procedure consists of the following major steps separation of technetium from the sample, thermal neutron irradiation of the Tc fraction to produce °°Tc, post-irradiation separation and purification of °°Tc from other activated nuclides, and counting of the 16 s Tc in a low-background P counter. The estimated detection limits for Tc in this procedure are 5 x 10 g in filter paper and 9 x 10 g in vegetable samples. 

Neutron activation analysis (NAA), based on the interaction of the object material with fast neutrons, has been used in the identification and determination of the content of elements present in pigments, coins and alloys, stone, glass, and pottery [26]. Multi-elemental analysis (about 20 elements) can be performed on small samples off less than 5 mg, with sensitivities in the ppm range. The requirement of a nuclear reactor, the handling of radioactive materials, and the time-consuming procedures required for preparing the samples are the main drawbacks of this technique. 

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