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08 July 2008

Answer to Question #3036 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:

I have been doing some experimentation with ¹⁰⁹Cd. I realize that it is a gamma emitter, but I don't have a gamma counter. We get counts with the liquid scintillation (LS) counter. My question: is it all right to use LS for ¹⁰⁹Cd? We are using the activity in a relative sense, comparing treatments with controls.

Cadmium-109 has an electron capture (EC) decay mode, with an 18 kiloelectron volt (keV) k-shell auger emitted 13% of the time, and various 22 to 25 keV k-shell x rays 65% of the time. This also feeds ^109mAg, which has similar energy x rays 35% of the time, and a couple high-yield conversion electrons from 63 to 84 keV 85% of the time. I would expect you would have very good counting efficiency with LS counting. If you don’t have a great deal of sample quenching, I’d expect you’d have good relative counting with LS. However, to take advantage of all these x rays, which will provide photoelectrons within the LS cocktail, and conversion electrons, you may try raising the upper end of the tritium window, or reducing the lower the end of the ¹⁴C window on your LS counter. You would then have all your counts falling in one range of energies.

David J. Allard, CHP

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