NEUTRON ACTIVATION ANALYSIS

BY GIAN VARGAS

Purpose of method

This method was founded sometime in 1936 by Hevesy and Levi when they found that some rare elements become radioactive after exposure to neutrons.

Neutron Activation Analysis is used in a variety of Scientific disciplines, examples would be biology, archaeology, anthropology, and geology.

Its archaeological use arose sometime in the mid 1950’s to investigate archaeological problems when a group of scientists, whom were working at the Brookhaven National Laboratory, saw the method’s potential for the relating of artifacts to source materials through their chemical structures.

This method is used in determining the concentration of elements in a varied amount of materials.

Its is known for its extreme accuracies in determining the elemental compositions of samples.

Relevance in Forensic Science

• Since this method is used widely in the field of scientific analysis, it’s a no-brainer that NAA would be used in the realms of Forensic Science.

• Therefore its is used effectively in the analysis of gunshot residue, and analysis of the amounts of arsenic in hair.

• Types of evidence used in NAA would include hair samples, bullet casings, and paint chips.

Chemical Principles involved

• This analytical technique bases its principals on the capturing of neutrons

• A nucleus captures a neutron soon after collision and proceeds to get into an active state which then begins to release amounts of gamma rays, and thus the nucleus remains in an unstable state releasing gamma rays from radioactive decay and helping identify the chemical identity of the target nucleus.

Advantages

• Its incredible in producing bulk amounts of analytical material without destroying the sample(s) themselves.

• This makes such a technique widely appilicable not only in the fields of forensic science but in other disciplines such as earth sciences and the semiconductor industries.

• As I have afore mentioned its biggest use is in the archaeological fields when examining artifacts.

• And lastly, its cost-effective!

Disadvantages

• In order to properly use this method you must attain a “High-Flux” neutron source. Thus it must be performed in a proper laboratory setting.

• Also it is not a quick method, time is need for such a technique, as results can come back in a few weeks, depending on the half lives of the elements it may be longer or shorter.

• Also it cannot preform analysis on certain elements such as oxygen and carbon.

Case Example: Assassination of JFK

• The nation was shocked when President John F. Kennedy was assainated while in Dallas, Texas Nov. 22 1963.

• During this investigation, NAA was used to examine certain pieces of evidence such as bullet fragments to determine where the fragments came from, and paraffin wax cats taken from Lee Harvey Oswald’s hands to determine the amounts of gunpowder residue on his hands

• It was also used to support the “Magic Bullet” theory.

Sources

• http://22november1963.org.uk/jfk-assassination-neutron-activation-analysis

• http://acg.missouri.edu/NAA.html• http://www.becquerellabs.com/About-Neutron-Activation-

Analysis.html• http://archaeometry.missouri.edu/naa_overview.html• http://www.elementalanalysis.com/services/neutron-

activation-analysis-naa/