Neutron Activation Analysis
Neutron Activation Analysis
Neutron activation analysis (NAA) is one of the most sensitive and specific nuclear process used for determining the concentrations of elements (trace quantities) in a vast amount of materials such as terrestil , lunar and meteoritic materials, marine sediments, air borne particles, natural water, biological material, hair, drugs, coal, petroleum and blood etc.The principle involved in neutron activation analysis consists of first irradiating a sample with neutrons to produce specific radionuclides. After the irradiation, the characteristic gamma rays emitted by the decaying radionuclides are quantitatively measured using gamma spectroscopy, where the gamma rays detected at a particular energy are indicative of a specific radionuclide's presence. Data analysis then yields the concentrations of various elements in the samples being studied.
When an element is made radioactive by placing it in a homogeneous flux of energatic charged particles of neutrons, the activity produced in the element is given by-
A = Nφσ(1 − eλt)
or, A = Nφσ(1 − e0.693t/t1/2)
where-
N = Number of atoms of the nuclide in the sample capable of forming radio isotope in question
φ = Neutron flux (i.e. number of neutrons cm-2s-1)
σ = Neutron capture cross section in cm2 for the given target nuclei
t = Time of irradiation
t1/2 = Half life of nuclear species produced
λ = Decay constant in sec-1 of the radioactive product.
Advantages of Neutron Activation Analysis
Compared to traditional material analysis methods, neutron activation analysis offers a number of advantages, such as-1. Non-destructive:
There is no risk of damage for samples subjected to NAA, which is ideal for analysis applications involving delicate or rare materials (e.g., archeological or anthropological findings).
2. Broad versatility and high sensitivity:
Neutron activation analysis can be used to identify a broad range of elements, even those in a very low concentrations in a small sample.
3. Fast processing time:
The analysis technique can detect and measure all of the elements within a sample simultaneously.
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