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19 March 2010

Answer to Question #157 Submitted to "Ask the Experts"

Category: Radon

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

Why is the dust wiped from my TV tube's face radioactive (10 times background)? It rapidly decays to near background within hours. My other house dust is not radioactive. Can soft x rays be responsible?

The radioactivity on your TV screen is due to short-lived radon-222 decay products (polonium-218, lead-214, bismuth-214, and polonium 214) that were produced in the air and have been collected on the surface of your TV screen. The electrostatic charge on the tube attracts dust particles and free ions from the air. The radioactivity is due to a combination of a collection of dust with radon decay products attached and a collection of unattached radon decay product ions and ion clusters. The greater activity on the tube compared to other household dust is probably due to there being more dust on the tube than on other surfaces and due to the collected ions.

Charles E. Roessler, PhD, CHP

A quick search of the literature about radon decay products on TV screens turned up the following note by Robert M. Boyd in the Health Physics Society's Newsletter, December 1986, page 24.

Inexpensive Indoor Radon Test—In that a color television is an excellent collector of the radon-222 daughters ever present in indoor air, the screening method described below may afford a simple and inexpensive test for determining indoor radon problems. Preliminary studies show a very strong electrostatic attraction of tiny dust particles to which radon daughters are attached to the television screen. By wiping the television screen and analyzing the residue, one can roughly correlate the concentration of radon daughters in the air. If done when the radon level is expected to be high because of meteorological or other conditions, this method might determine whether a more accurate and detailed study is needed. If perfected and refined, this method would provide a fast way to evaluate a large number of homes and other indoor environments for a potential radon hazard.

Procedure:

Turn on your color TV set for approximately four hours.
Turn off the set and wait four hours. (Collection is best when the set is off for awhile.)
Now with your finger tips, thoroughly wipe the entire screen of your TV set with a paper tissue slightly dampened with rubbing alcohol.
Immediately check the wipe (smear) with a Geiger counter, using a thin-window pancake probe. A typical number is 6,000 counts per minute.

Gen Roessler, Editor HPS Web Site

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