How I Screwed Up My Radon Test

OK, I’m stupid.

Here are the details. I dutifully followed the directions (mostly) on the Pro-Lab radon testing kit. I placed the two detector-vials on a flat surface in my basement, more than 2 feet above floor and 3 feet away from walls. After the prescribed 96-hour testing period, I capped the detectors, and then carefully put them in my desk drawer for later mailing to Pro-Lab. The latter action was my screw up. I should have immediately mailed them to Pro-Lab for reading. By sticking the detectors in my desk I demonstrated a fundamental misunderstanding of the nature of the thing I was testing for.

This is as good an entree as any to the properties of radon.

As every real estate agent has heard repeatedly, radon is a colorless, odorless, naturally-occurring gas. It is the heaviest of the noble gases, which are a group of elements that don’t easily react with other elements. Helium, neon, and argon are the better known noble gases that we encounter in our daily lives. Radon is also radioactive. It is this property in combination with its inertness as a noble gas that makes it such a troublemaker.

Naturally occurring uranium in the ground is the ultimate source of radon. Uranium-238, the most common isotope, is weakly radioactive. Over the course of time—a long time—it decays to lead-206. I say “a long time” because uranium-238’s half-life, or the time it takes half the radioactive atoms in a sample to decay, is 4.5 billion years. By the way the much rarer isotope, uranium-235, in a highly enriched form, was the explosive (fissile) material for the “Little Boy” atomic bomb dropped on Hiroshima.

As you can see on the chart above, the chain of radioactive decay from uranium-238 to lead-206, a process known as transmutation, is quite long. Radon sits in the middle, more or less. Under normal conditions the elements above radon in this chain are solids, and, as such, stays fixed in the soil. However, when radium-226 decays to radon-222 things change. Radon, as reported above, is a gas, and, more specifically, a noble gas, a gas that doesn’t chemically interact (or bond) easily. It’s a free spirit, so to speak, and migrates to the earth’s surface through pores in rock/soil and ground water. For reasons I will delve into later, radon tends to concentrate in the basement levels of buildings.

Radon is highly radioactive. Its half-life is 3.8 days. It decays by emitting an alpha particle to become polonium-218. Polonium-218 decays in similar fashion to lead-214 (radioactive). Lead-214 emits a beta particle to form bismuth-214, et cetera. Each of the successive progeny of radon emits either an alpha or beta particle as the decay chain continues towards lead-206. Both types of radiation pose health hazards.

If radon was the last stage before non-radioactive lead-206, it probably wouldn’t pose a serious environmental issue. Although we might inhale it, we would likely exhale it in the next breath. In any case the next element in the decay chain would be the non-radioactive lead-206. While lead is an environmental hazard, the concentration we’re talking about here is extremely small and wouldn’t by itself create much of a hazard (lead from old paint is a completely different story).

But radon isn’t the penultimate decay stage. The elements it transmutes into are chemically reactive solids as opposed to inert gases. Polonium-218, lead-214, bismuth-210, and the rest of the radioactive progeny, are likely to attach themselves to dust particles and tobacco smoke, which, in turn, become lodged in lung tissue, where radioactive emissions in the form of alpha and beta particles can do real damage.

Now back to my original act of gross stupidity...the purpose of the detector-vials that I left open for 96 hours in my basement was to collect a representative sample of radon, whose radioactivity then has to be measured by a lab. Problem is the radon within the capped detector-vials doesn’t stay “radon.” It decays into polonium, lead, bismuth, etc., each of which has its own characteristic half-life, so when the lab measures radioactivity a few days after the vials are capped and mailed, it actually measures the radioactivity of the mixture of elements created by radon’s decay, each of whose concentration is constantly changing. Obviously there’s a time relationship between radioactivity and the original radon concentration, but I suspect the longer you wait, the more sources of error creep into the reading. As it costs $30 to read my radon test, I will opt to repeat it rather than risk a bad reading because I delayed shipping the test vials to the lab.