NATS 1575 Chapter Notes - Chapter 12: Neutron Activation Analysis, Neutron Activation, Emission Spectrum

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16 Aug 2016
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Chapter 12 // Metals, Paint, and Soil
Introduction
-many manufactured products and even most natural materials contain small quantities of
elements, knows as trace elements, present in concentrations of less than 1%.
-for the criminalist, the presence of these trace elements is particularly useful, because they
provide “invisible” markers that may establish the source of a material or at least provide
additional points for comparison.
Neutron Activation
-nuclear chemistry provides a new tool for identifying and quantitating the elements
-a nuclear reactor is simply a source of neutrons that can be used for bombarding atoms,
causing some neutrons to be captured to produce radioactive isotopes (atoms with the same
number of protons but a different number of neurons).
-To identify the radioactive isotope, it is necessary to measure the energy of the gamma rays
emitted as radioactivity.
-Neutron activation analysis measures the gamma-ray frequencies of specimens that have been.
bombarded with neutrons
-This method provides a highly sensitive and nondestructive analysis for simultaneously
identifying and quantifying 20 to 30 trace elements.
-Forensic analysis has employed neutron activation on find trace elements in metals, drugs,
paint, soil, gunpowder residue, and hair.
Paint
-Paint spread onto a surface will dry into a hard film that can best be described as
consisting of pigments and additives suspended in the binder.
-One of the most common types of paint examined in the crime laboratory involves finishes
emanating from automobiles.
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