Can a pancake geiger counter be used to estimate radon?

Submitted by Anonymous on Mon, 2012-02-06 20:33

If a pancake-style geiger counter (one that has a mica window to detect alpha) is used, can radon be estimated?

i.e., if one were to measure a background average of a room with the mica window uncovered, and then cover the mica window, and take the background average again (and maybe run it a few more times both ways just to make sure neither was a one-off), the difference should be the contribution of alpha. Would the amount of this alpha radiation be a rough estimate of radon levels?

And if so, at what point (how many CPM difference between the two measures) would suggest a potential radon issue and that a proper radon test might be a good idea?

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The basic answer is no. A

Submitted by bandstra on Tue, 2012-02-21 23:00.

The basic answer is no. A detector that only detects alphas is really required (see, e.g., the EPA radon webpage or the National Radon Proficiency Program website for examples of detector systems).

The reason is that the natural background of betas and gammas is much higher than the number of alphas you would expect, and it creates a signal-to-noise problem. The EPA recommends a maximum radon activity concentration of 4 picocuries per liter (0.15 Bq/L). Even at this level of activity, a rough calculation says there would only be about 1 excess count from radon every few minutes (assuming a ~5 cm diameter pancake and ~15% efficiency for detecting alphas). This means that if you take that detector and make two measurements — one with paper covering the mica window and the other without — it could take several days per measurement to see a statistically significant difference between the two measurements (this depends strongly on the background rate; I assumed 30 counts per minute). But even if this measurement were possible and yielded a positive result, it would be nearly impossible to back out the actual concentration in the air.

The Health Physics Society website notes that you could use a Geiger counter to estimate radon concentration by pulling air through a filter and then putting the filter in front of the detector, but there are problems associated with accurately interpreting these results as well.

Mark [BRAWM Team Member]

Thanks for your reply. Very

Submitted by Anonymous on Wed, 2012-02-22 21:18.

Thanks for your reply. Very helpful.