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Neutron Activation Analysis

Introduction

Neutron Activation Analysis (NAA or INAA for Instrumental Neutron Activation Analysis) is a radiochemical method of analyis that uses neutron irradiation of a sample to convert analyte elements to radioactive isotopes. The radioactive elements can then be detected and quantified by gamma-ray spectroscopy.

The usual procedure to perform NAA is to irradiate samples and standards in a reactor chamber for a period of time of minutes to hours, remove and allow to "cool" for a period of time, and then count. The cooling period allows short-lived radioactive species to decay away that might have interferred in the counting of the analyte and makes the irradiated samples safer to handle.


Instrumentation

The typical neutron source for NAA is a nuclear reactor. NAA is also possible using a discrete neutron source or an accelerator. Samples are usually sealed in a polyethylene vial and can be a solid, liquid, gas, slurry, etc.

A variation of NAA is prompt gamma-ray activation analysis (PGAA). In PGAA the gamma-ray emission is recorded as a sample is irradiated with neutrons. This method is useful for a few elements, such as B, Cd, and S, which are not amenable to regular NAA.


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