neutron activation analysis contents: introduction principle diagramatic represetation fundamental requirements merits sensitivity demerits references

1. Analytical Chemistry
chem 420
Presenter: Muzammal zia
Spring 2019
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2. Presentation topic
Merits and demerits of NAA
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3. Table of contents
Topics Slide no
Introduction of NAA 4
Principle of NAA 5
Diagrammatic representation 6
Fundamental requirements 7
Merits of NAA 8
Demerits of NAA 17
References 22
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4. Introduction of NAA
 G. Hevesy and H. Levi introduced this method in 1936
 NAA is a method that is used for qualitative and quantitative determination of
elements based on the measurement of characteristic radiation from radio nuclei
formed directly or indirectly by neutron irradiation of material.
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5. Principle of NAA
 Sample is bombarded with neutron
 Neutron capture reaction would occur
 Neutron would transfer its energy to nucleus
 Nucleus becomes unstable and emit gamma rays to get stable compound
nucleus
 If compound nucleus is stable, PGNAA is observed
 If compound nucleus is unstable, it will emit gamma rays along with Beta
Particles and termed as DGNAA
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6. Diagrammatic representation
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Fig.1 NAA

7. Three fundamental requirements for NAA
 Source of neutron
 Instrument that is used for the measurement of x-rays that are emitted during
reaction
 Which type of reaction doing during the NAA
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8. Merits of NAA
 Very sensitive method
 Selective method
 We get accurate results
 This method is used as reference or standard method
 Used for elemental analysis
 Used for major, minor, minute or trace elements
 It has wide range of applications in every field of life
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9. Continue……
 Pre treatment of samples is normally not required
 No sample digestion(does not need of chemical treatment)
 No extraction
 No volume loss
 No dilution required
 No potential for contamination due to handling or laboratory chemicals
 One simple procedure can analyze 30+ elements simultaneously
 High sample volume capabilities
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10. Continue……
 Non-destructive
 Can analyze multiple element samples
 Inherent capability for high levels of accuracy
 Significant matrix independence as most sample are transparent to both neutron
and gamma rays
 The use of radiochemical separation to overcome interference in complex
gamma-ray spectra
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11. Sample size
 Simplicity of sample treatment before analysis
 Sample reduced to a size suitable for encapsulation prior to conducting the
irradiation procedure
 Suitable sample mass may vary from milligrams to several grams of sample
 Small sample sizes (0.1 mL or 0.001 gm)
 Suitable for determination of masses in the order of 10-6 to 10-9.
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12. No potential for contamination
 In order to avoid the potential for contamination, samples are weighed into
vessels appropriate for the type of irradiation to be performed under Class 1000
clean room conditions.
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13. Detection limit
 The ability of an analytical method to determine the minimum/lowest amounts
of an element/sample present with complete certainty /reproducibility.
 It can be achieved by optimizing irradiation parameters (Energy, Fluence rate of
neutrons, times of irradiation, counting)
 Very low detection limits for 30-40 elements
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14. Sensitivity
 Ability to sense the analyte in the sample of NAA with acceptable reliability.
 Based on nuclear parameters(neutron cross section, half-life, gamma-rays
abundance)
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15. Self-validating
 It is self-validating
 Two or more analytical gamma lines may be used for the determination of same
element, allowing a cross-check of the process
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16. Significant matrix independence
 H, C, O, N, P, and Si (matrix-forming elements) hardly form any radioactive
isotopes (so less matrix effect)
 Significant matrix independence as most samples are transparent to both
neutron and gamma rays
 The chemical form and physical state of the elements do not influence the
activation and decay process as the vast majority of samples are transparent to
both the probe and the analytical signal(the gamma rays)
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17. Demerits or limitations of NAA
 There must be a source of neutrons
 Not all elements are detectable
 It cannot perform analysis on certain elements such as oxygen and carbon
 Some trace elements that we do not determine are P, Mn, Hg, Cu, Hg, Mo, Dy
 Some of these elements(Mn, Mo) are determined by other INAA labs
 Hg and Mo can be determine when they are in much higher concentrations
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18. Slow technique
 It is not a quick method
 It is often time demanding
 Results obtain up to 2-4 weeks
 Depending upon the half lives of the elements
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19. Chemical limitation
 It only gives information on the total concentration of an element
 Inability of this technique to distinguish the chemical nature(bonding, structure,
ionization state) and physical state of the element under consideration
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20. Nuclear limitation
 Interferences may arise if different elements in the sample emit gamma rays of
nearly the same energy
 Changes in the irradiation conditions resulting when the sample is inserted in the
neutron flux
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21. Less common
 Less common than other analytical techniques due to necessity of having access
to a nuclear reactor or neutron generator
 Not all laboratories have access to a nuclear reactor
 Initial equipment costs for Ge(Li) spectrometry and irradiation facilities are high
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22. References
 Win, D. (2004). Neutron activation analysis (NAA). AU J Technol, 8(1), 8-14.
 Filby, R. H., and Shah, K. R.(1974). Activation analysis and applications to
environmental research. Toxicological and Environmental Chemistry, 2(1), 1-44.
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23. References
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