Neutron activation analysis: Difference between revisions
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'''Neutron activation analysis (NAA)''' is an extremely sensitive technique of [[radiochemistry|radiochemical]] analysis used to determine the existence and quantities of major, minor and trace elements in a material sample. As opposed to other methods in analytical chemistry, such as [[mass spectrometry]] or [[chromatography]], it focuses entirely on the nuclei of atoms, not their molecular structure. | {{TOC|right}} | ||
'''Neutron activation analysis (NAA)''' is an extremely sensitive technique of [[radiochemistry|radiochemical]] analysis used to determine the existence and quantities of major, minor and trace elements in a material sample. As opposed to other methods in analytical chemistry, such as [[mass spectrometry]] or [[chromatography]], it focuses entirely on the nuclei of atoms, not their molecular structure. It reports the concentrations of all elements in a sample, down to extremely low levels. | |||
==Principle== | |||
When samples are irradiated with [[neutron]]s, they emit [[gamma ray]]s. "Samples with unknown elemental concentrations are irradiated with thermal neutrons in a nuclear reactor together with standard materials of known elemental concentrations. Neutrons are absorbed in the nuclei of constituent atoms, and later these nuclei emit radiation with energy and quantity characteristic of the particular element...This emitted radiation is a 'fingerprint' of the element, and the amount of radiation given off at a certain energy is indicative of the amount of the element present in the sample. A comparison between specific activities induced in the standards and unknowns provides the basis for computation of elemental abundances. From this analysis, a report is issued giving elemental concentrations in the unknown sample."<ref>{{citation | |||
| publisher = Nuclear Reactor Laboratory, [[University of Wisconsin]] | |||
| title = Neutron Activation Analysis Description | |||
| url = http://reactor.engr.wisc.edu/naa/UWNRNAA.htm | |||
}}</ref> | |||
==Comparison with other methods== | |||
===Advantages=== | |||
*Inherently nondestructive. "The sample is not permanently damaged by NAA, and in the case case of forensic analysis and analysis of rare samples, such as meteorites or archeological finds, the sample can be saved and even subjected to further analysis at a later time...the sample may become slightly radioactive in NAA, the radiation in the sample decreases with time until it reaches a state similar to which it was before the NAA was performed on it." | |||
*"detects the total elemental content, regardless of oxidation state, chemical form or physical location." <ref>{{citation | |||
| publisher = Nuclear Reactor Laboratory, [[University of Wisconsin]] | |||
| title = Advantages of NAA over other chemical analyses | |||
| url = http://reactor.engr.wisc.edu/naa/advant.htm | |||
}}</ref> | |||
*Simultaneously detects all elements in the sample | |||
*Time-efficient for analyzing many samples | |||
===Disadvantages=== | |||
*Need for neutron source | |||
==Major facilities== | |||
One major NAA research facility is the [[High Flux Isotope Reactor]] at [[Oak Ridge National Laboratory]].<ref>{{citation | One major NAA research facility is the [[High Flux Isotope Reactor]] at [[Oak Ridge National Laboratory]].<ref>{{citation | ||
| url = http://neutrons.ornl.gov/facilities/HFIR/naa.shtml | | url = http://neutrons.ornl.gov/facilities/HFIR/naa.shtml | ||
| title = What is Neutron Activation Analysis? | | title = What is Neutron Activation Analysis? | ||
| publisher = Neutron Sciences, [[Oak Ridge National Laboratory]]}}</ref> | | publisher = Neutron Sciences, [[Oak Ridge National Laboratory]]}}</ref> | ||
==References== | |||
{{reflist|2}} | |||
Revision as of 11:26, 8 May 2010
Neutron activation analysis (NAA) is an extremely sensitive technique of radiochemical analysis used to determine the existence and quantities of major, minor and trace elements in a material sample. As opposed to other methods in analytical chemistry, such as mass spectrometry or chromatography, it focuses entirely on the nuclei of atoms, not their molecular structure. It reports the concentrations of all elements in a sample, down to extremely low levels.
Principle
When samples are irradiated with neutrons, they emit gamma rays. "Samples with unknown elemental concentrations are irradiated with thermal neutrons in a nuclear reactor together with standard materials of known elemental concentrations. Neutrons are absorbed in the nuclei of constituent atoms, and later these nuclei emit radiation with energy and quantity characteristic of the particular element...This emitted radiation is a 'fingerprint' of the element, and the amount of radiation given off at a certain energy is indicative of the amount of the element present in the sample. A comparison between specific activities induced in the standards and unknowns provides the basis for computation of elemental abundances. From this analysis, a report is issued giving elemental concentrations in the unknown sample."[1]
Comparison with other methods
Advantages
- Inherently nondestructive. "The sample is not permanently damaged by NAA, and in the case case of forensic analysis and analysis of rare samples, such as meteorites or archeological finds, the sample can be saved and even subjected to further analysis at a later time...the sample may become slightly radioactive in NAA, the radiation in the sample decreases with time until it reaches a state similar to which it was before the NAA was performed on it."
- "detects the total elemental content, regardless of oxidation state, chemical form or physical location." [2]
- Simultaneously detects all elements in the sample
- Time-efficient for analyzing many samples
Disadvantages
- Need for neutron source
Major facilities
One major NAA research facility is the High Flux Isotope Reactor at Oak Ridge National Laboratory.[3]
References
- ↑ Neutron Activation Analysis Description, Nuclear Reactor Laboratory, University of Wisconsin
- ↑ Advantages of NAA over other chemical analyses, Nuclear Reactor Laboratory, University of Wisconsin
- ↑ What is Neutron Activation Analysis?, Neutron Sciences, Oak Ridge National Laboratory