The Invisible Menace

The Invisible Menace

This season I’ll be in charge of radon monitoring in the caves. Monitoring occurs year-round on a weekly basis, mainly on tour routes. The purpose of radon monitoring is less for the protection of visitors and more for tour guides and cavers who log thousands of hours in the caves over the course of their tenure. Radon concentration changes weekly, so it’s imperative that the park staff remain up to date on their exposure levels.

The sequence of radon-222 decay products. Once an atom of radon decays, it transforms into a slew of radioactive heavy metals which undergo alpha and beta decay until finally becoming a stable atom of lead-206. Diagram taken from the Summary of ICRP Recommendations on Radon, 2018.

Radon is a naturally-occurring, colorless, odorless, and non-reactive gas. It is formed through the decay of uranium, which is present in nearly every solid substance in the environment. It does not chemically interact or linger inside your body. Despite this, radon is the second-leading cause of respiratory cancers after smoking. This is because radon is radioactive and decays via alpha emission. What makes radon particularly dangerous is that it decays into a series of radioactive atoms, some of which also undergo alpha decay. These radon decay products are all metal atoms which can aerosolize, attach to dust particles, and embed themselves in lung tissue. Alpha emissions within the body are especially harmful because they can damage DNA and lead to the development of lung cancer.

Using a small electric air pump and a filter, I collect cave dusts which contain the various slew of radioactive alpha-emitting atoms in the air. Radon is chemically inert, so this technique cannot reveal the true concentration of radon gas, only decay products.

Monitoring for radon is pretty simple. You can either measure the concentration of radon or of the decay products. Because decay products are more chemically reactive, it’s much easier to capture them. When we do a radon run, we use an electric pump with detachable filters and travel in 5-minute increments from site to site along an established route. The air pump and filters collect cave dust. Once a 5-minute sample is taken, it must be analyzed for alpha emissions. Filters are analyzed one-by-one in an alpha counter. The number of alpha decays and the age of the sample (in minutes) can be input into an equation to receive working levels. I will explain working levels in a future blog, but these are the numbers which determine how much exposure one would receive when working in a particular section of the cave.

Here I am about to test a sample for alpha particles. The white filter contains cave dusts and radon decay products. The alpha counter records alpha emissions, which can be used to calculate exposure, or working levels.
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