# I How accurate are radon detectors?

1. Nov 30, 2018

### SteveUSA

I was looking online at detectors in the $150-$200 range, queried a seller's website, asked how the electrons or helium nuclei (aka alpha particles) from radon could be discriminated from other sources. The reply:

"Rn222 is the only thing the monitor measures and it is relatively unaffected by anything else. The radon chamber uses passive diffusion and alpha spectrometry to count Rn222 alpha particles - this is achieved through a silicon photo diode. Other particles and rays are discounted through our algorithm."

So do the helium nuclei have a specific energy level that can be distinguished from other sources? Is a detector in this price range accurate enough to justify purchase?

2. Dec 1, 2018

### gleem

Radon is unique in its radiation signature in that there are almost no other common airborne high energy alpha particle emitters in the environment. Any gamma or beta ray will have significantly less energy.

Your concern for discrimination of radiation is important but also is the sensitivity. What levels of radon do they claim that they can measure. Could you post a link to the manufacturers website?

If you are interested in determining the concentration of radon in your home I would advise you to obtain a radon kit from a reputable monitoring service and let them determine the hazard level. Accurate determination of radon levels is not trivial. I do not think it is a good DIY project.

3. Dec 1, 2018

### SteveUSA

I thank you for the reply. I actually did run a test 15-20 years ago with a $20 sample collector purchased from, and analyzed by, the University of Pennsylvania, which reported 4.0 picocuries/liter, on the threshold of concern. I wanted to check for potential changes and started researching detectors. The site is https://airthings.com/us/ and the product is at https://store.airthings.com/us/corentium-model-qri-digital-radon-monitor.html (if that link doesn't work, it is the Corentium detector currently selling for$179). I did not see any specs for precision or accuracy, so I asked and received the reply I quoted in my original post. I see now, following the second link, that the "uncertainty" is 10% even after a month, not too impressive.

4. Dec 1, 2018

### Staff: Mentor

Radon in a basement is due to the balance between up welling of radon from the ground and exchange of air from the closed space to the outside. Given that, I would expect the balance to be variable in time. To determine a trend, I would want to see a plot of daily samples over a period of years. The plot would show both variability and trend, and if the ratio of variability to trend is too large, the unreliability of the trend estimate.

Let's say that the accuracy of the instrument yields a reading biased high or low. If the bias is constant, that would not change the trend. If the bias is not constant, then it is another source of variability.

It sounds like a fun project, but one in which statistical handling of noisy data is perhaps more important than selection of the instrument.

5. Dec 1, 2018

Staff Emeritus
I'm having a hard time figuring out what your question is. Can this detect radon at all? Sure. Is the precision 1%? Surely not. But I feel your real question is somewhere in between. What do you want to know?

6. Dec 1, 2018

### SteveUSA

I was checking for whatever response I might get, ranging from "those are crap" to "oh yeah, I used one and it matched readings from other instruments".

I would not trust a single instrument. Without at least 2 methods which agree, no way to be confident.