Neutron Activation Technique

When bombarded with free neutrons, nuclei briefly capture the free neutrons, becoming excited, but this effect quickly wears off.

Neutron activation analysis is a sensitive, accurate means of quantifying a sample's trace element concentrations. The sample, which could be anything from a piece of metal to a work of art, is bombarded with free neutrons, exciting its nuclei and making them heavier. The nuclei decay, emitting a beta particle and, almost always, gamma rays. A high-resolution gamma ray spectrometer detects these rays for quantitative and qualitative analysis. Neutron activation technique is non-invasive, with no need for sample prep or solubilization. While it briefly induces radioactivity, this effect soon disappears, making it possible to analyze even delicate materials with neutron activation.

Things You'll Need

• Nuclear reactor with uranium fission
• High-resolution gamma ray spectrometer

Instructions

1. Obtain element "standards," which are samples with known concentrations of the elements whose concentrations you want to measure. You will be quantifying gamma ray emissions of your standards and comparing them to gamma ray emissions of the sample you want to study, in order to figure out element concentrations in your unknown sample. In this way, you will be able to use neutron activation to analyze concentrations of most elements, with a few exceptions that do not respond to neutron activation: boron, carbon, oxygen and aluminum.

2. Place both your unknown sample, of which you are measuring concentrations, and your standard sample, of which you already know the concentrations, a few inches from a nuclear reactor with uranium fission. Switch on the nuclear reactor to bombard the sample with neutrons.

3. Use a high-resolution gamma ray spectrometer to detect the "delayed" gamma rays from the sample.

4. Calculate the concentration of the sample from the spectrometer data. This concentration is a product of the standard concentration, the ratio of the standard weight to the sample weight, and the ratio of sample activity to standard activity.

Tips & Warnings

• Nuclear reactors and nuclear materials are radioactive and highly dangerous. Heed all posted warnings and follow all posted safety procedures.

References

• Illinois State Archaeological Survey: "An Overview of Neutron Activation Analysis"; Michael D. Glascock; 2004

Resources

• Australian Nuclear Science and Technology Organization: Neutron Activation Analysis