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20 November 2008

Answer to Question #5970 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Rocks, Minerals, and Mines

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

I am a geology student. I recently came across a sample of what I think was autunite in a box of sulfur. I performed a streak test on it, looking for the distinctive smell, but it didn't have any odor. It just so happened that my lab partner and I were analyzing clay samples using a scintillometer. We picked up an unusual amount of radiation from this sample that we thought was sulfur after I had sniffed the streak plate. It was giving us a reading of >7,500 counts per second at a distance of 12 cm. I'm concerned about my health. How harmful is inhaling autunite dust? Should I consult someone? I would really appreciate any information or advice you could give me.

As you know, autunite contains uranium and is therefore radioactive. Uranium decays through a chain of radionuclides, the exact nature of which depends on which isotopes of uranium were present initially. The emanation consists of a mixture of alpha, beta, and gamma radiation.

Radiation counts from radioactive materials reach very large numbers from very small quantities. The original unit of radioactivity, the curie, was first defined as the activity in a gram of radium. It was later specified as 37 billion disintegrations per second.

The radiation you detected from your sample was thus low level. The quantity of radioactive material was extremely small. This can be compared with other natural sources of radiation to which we are all exposed. Outdoor air in the United States contains an average of 0.4 picocuries of radon and its radioactive decay products per liter, or 3.7 x 10^-3 disintegrations per second. The average American receives a dose of 3 millisievert (mSv) per year from natural radiation. About 2 mSv of this comes from inhaling radon and its radioactive progeny in air. The remaining 1 mSv is divided approximately evenly among cosmic, terrestrial, and internal sources. The human body is slightly radioactive, mostly due to potassium-40. All of this is from natural radiation that has been with us since the beginning of time. Man-made radiation contributes another 0.6 mSv per year, mostly from medical exposures.

Conclusion: You may have received a very small radiation dose from your autunite. However, it did not significantly alter your dose due to other natural radiation in the environment.

S. Julian Gibbs, PhD, DDS

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