Answer to Question #10445 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Surveys and Measurements (SM)

The following question was answered by an expert in the appropriate field:

Q
I need to perform a study to determine the uranium concentration in drinking water. I have a high-purity germanium detector in my laboratory. Is it possible to use the gamma spectrometry to perform the study? If so, can you please brief me on how to go about it?
A

There are numerous methods of analysis for uranium in water. The method in which gamma spectrometry is used generally relies on the presence of certain gamma-emitting radioactive progeny of 238U, such as 214Pb and 214Bi. The difficulty with such an analysis is that in water samples there is a high likelihood that these progeny will not be in radioactive equilibrium with the parent uranium. You may be able to analyze for 226Ra using the gamma measurements from these progeny by placing the sample in its counting container and sealing it (leaving a minimum free air space) and allowing a few weeks for the radon and subsequent progeny to achieve equilibrium with the radium and then doing the gamma spectrometry measurements. Unless you know that the radium is also in equilibrium with the uranium (and this is generally unlikely in water samples), you cannot assume that the uranium activity is the same as that of the radium.

In most cases you would have to use other techniques, such as electrodeposition and alpha counting or chemical fluoroscopy to do the uranium analysis. Here are some links to analytical methods and their descriptions that you might find useful. Good luck.
  1. Oak Ridge Associated Universities link to approved procedures. Click on the pdf link to Environmental Protection Agency methods.
  2. Link to Environmental Measurements Laboratory Procedures HASL-300.
  3. Link to Environmental Protection Agency analytical methods.

George Chabot, PhD

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