Neutron activation analysis measurement

For the investigation of meteorites various experimental methods are applied, in particular mass spectrometry, neutron activation analysis, measurement of natural radioactivity by low-level coimting and track analysis. The tracks can be caused by heavy ions in cosmic radiation, by fission products from spontaneous or neutron-induced fission and by recoil due to a decay. Etching techniques and measurement of the tracks give information about the time during which the meteorites have been in interstellar space as individual particles (irradiation age). 

Figure 17.7 Calculated MDA of iodine as a function of sodium concentration in a sample by neutron activation analysis. Measurement condition neutron flux, 7 x 10 cm s sample weight, 0.1 g irradiation time, 30s counting time, 5min.

Measured by neutron activation analysis Measured by difference... 

The concentration of Ni in a new alloy is determined by a neutron activation analysis using the method of external standards. A 0.500-g sample of the alloy and a 1.000-g sample of a standard alloy known to contain 5.93% w/w Ni are irradiated with neutrons in a nuclear reactor. When irradiation is complete, the sample and standard are allowed to cool, and the gamma-ray activities are measured. Given that the activity is 1020 cpm for the sample and 3540 cpm for the standard, determine the %w/w Ni in the alloy. 

Thorinm-232 is the only non-radiogenic thorium isotope of the U/Th decay series. Thorinm-232 enters the ocean by continental weathering and is mostly in the particulate form. Early measurements of Th were by alpha-spectrometry and required large volume samples ca. 1000 T). Not only did this make sample collection difficult, but the signal-to-noise ratio was often low and uncertain. With the development of a neutron activation analysis " and amass spectrometry method " the quality of the data greatly improved, and the required volume for mass spectrometry was reduced to less than a liter. Surface ocean waters typically have elevated concentrations of dissolved and particulate 17,3 7,62... 

A modem technique for nitrogen detn is known as fast neutron activation analysis. Materials such as RDX are exposed to a high density fast neutron flux which converts the 14N content of the sample into unstable 13N. The N is detd by measuring the 13 N produced by the 14N (n, 2n) 13N reaction. This technique is extremely sensitive, but requires specialized instrumentation (Refs 44, 51 61)... 

Neutron activation analysis (NAA) is a technique for the qualitative and/or quantitative determination of atoms possessing certain types of nuclei. Bombarding a sample with neutrons transforms some stable isotopes into radioactive isotopes measuring the energy and/or intensity of the gamma rays emitted from the radioactive isotopes created as a result of the irradiation reveals information on the nature of the elements in the sample. NAA Is widely used to characterize such archaeological materials as pottery, obsidian, chert, basalt, and limestone (Keisch 2003). 

Wiernik and Amiel [411] used neutron activation analysis to measure lithium and its isotopic composition in Dead Sea brines. 

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. 

Differentiation of inorganic and organic mercury can be achieved in a number of different ways, many of which depend upon the reduction and vapourisation of the inorganic mercury, followed by reduction [84] or oxidation [85,86] of the organic mercury compounds, and a final measurement by atomic absorption or mass spectrometry. Similar methods of separation of the inorganic and organic components are used in the pretreatment of samples where the final analysis for mercury is to be made by neutron activation analysis [87,88]. 

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. 

In Gubbio, Italy, a 1 cm layer of clay between extensive limestone formations marks the boundary between the Cretaceous and Tertiary Periods. This clay layer was known to have been deposited about 65 million years ago when many life forms became extinct, but the length of time associated with the deposition was not known. In an attempt to measure this time with normally deposited meteoritic material as a clock, extensive measurements of iridium abundances (and those of many other elements) were made on the Gubbio rocks. Neutron activation analysis was the principal tool used in these studies. About 50 elements were searched for in materials like the earth s crust, about 40 were detected and about 30 were measured with useful precision [26-28]2. 

The y particle is emitted virtually instantaneously on the capture of the neutron, and is known as a prompt y - it can be used analytically, in a technique known as prompt gamma neutron activation analysis (PGNAA), but only if such y s can be measured in the reactor during irradiation. Under the conditions normally used it would be lost within the nuclear reactor. In this reaction, no other prompt particle is emitted. The isotope of sodium formed (24Na) is radioactively unstable, decaying by beta emission to the element magnesium (the product nucleus in Figure 2.13), as follows ... 

Glascock, M. D. and Neff, H. (2003). Neutron activation analysis and provenance research in archaeology. Measurement Science and Technology 14 1516-1526. 

Studies of the inorganics in cotton dust have incorporated the use of a wide variety of techniques. These include X-ray fluorescence spectroscopy, atomic absorption spectroscopy, electron microscopy, energy dispersive analysis of X-rays, X-ray diffraction, atomic absorption spectroscopy, neutron activation analysis and petrographic microscopy. It is necessary to use a wide array of techniques since no single technique will permit the measurement of all trace elements. Steindard chemical techniques to determine the ash content of samples and of various extracts have also been used. In most of these studies the ash fraction has been considered to be a reasonably accurate measure of the inorganic content. 

A method has been developed for the determination of technetium-99 in mixed fission products by neutron activation analysis Tc is separated from most fission products by a cyclohexanone extraction from carbonate solution, the stripping into water by addition of CCI4 to the cylohexanone phase, and the adsorption on an anion exchange column. Induced Tc radioactivity is determined using X-ray spectrometry to measure the 540 and 591 keV lines. The sensitivity of the analysis under these conditions is approximately 5 ng. The method has been successfully applied to reactor fuel solutions. 

Sheppard 1980). The level of thorium measured in 1969 in East Chicago, IN, a heavily polluted industrial area, was 1.3 ng/m compared to a value of 0.27 ng/m at a rural location in Michigan (Niles, Ml) (Dams et al. 1970). The air particulate samples collected from 250 sites in the United States by the National Air Surveillance Network (NASN) of ERA during 1975 and 1976 were analyzed for thorium-232 by neutron activation analysis. The measured concentrations at 250 urban and nonurban sites in the United States ranged from 0.2-1.0 ng/m, with a mean concentration of 0.3 ng/m (Lambert and Wilshire 1979). The mean concentrations of thorium-228, thorium-230 and thorium-232 in New York City air (sample collected on the roof above the 14th floor) were 36 aCi/m (aCi = 10 Ci), 36 aCi/m, and 37 aCi/m, respectively (Wrenn et al. 1981). 

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