Lucas cell

A Lucas cell is used to grab a gas sample, filter out the radon daughters through a special filter at 0.01 micrometres, and then counts the radioactive decay of radon gas. The inside of the 1-liter gas chamber is coated with silver activated zinc sulphate or ZnS(Ag) that scintillates or shines when struck by alpha particles. A cone shaped 5 inch photomultiplier tube at the top of the chamber counts the photons and sends the count to the data logger or counter.

Radon itself is an inert gas, much like Helium, Argon, Xenon, and Krypton gas. Its danger lies in the fact that its daughters accumulate in the dust in your house. The Radon Daughters are radioactive solids that lodge in your lungs and bombard them with alpha and beta radiation.

If you need a sample of radon daughters wipe your computer monitor or TV - the black stuff is radioactive. In addition, plastic grocery bags, if left in a high radon environment collect radon daughters due to static charge. The EPA recommends a radon level of no more than 4 pCi/l in the air. The average in my home is 2.4-3 pCi/l. On a rainy, low barometer day I have measured up to 7 pCi/l. The Eberline provides 660 V dc to operate the photomultiplier tube and returns real time data in counts per minute. Alternatively, picocuries per liter (pCi/l). It’s the fastest way to measure radon gas, easily! Radon seeps up fast in high precipitation events and low barometers.

For this example, we will use the uranium decay series that begins with Uranium 238, since its radon has the longest half-life and it poses the most danger to humans. The decay chain is as follows:

$238U\Rightarrow 234Th\Rightarrow 234Pa\Rightarrow 234U\Rightarrow 230Th\Rightarrow 226Ra\Rightarrow 222Rn$

Natural Radium-226 decays into Radon-222 and becomes a gas from a solid. Radon-222 has a half-life of 3.82 days and is transported up through the soil. It decays into radon daughters, forming a solid again. Radon daughters from 222Rn then continue as follows:

$218Po\Rightarrow 214Pb\Rightarrow 218At\Rightarrow 214Bi\Rightarrow 214Po\Rightarrow 210Tl\Rightarrow 210Pb\Rightarrow 210Bi\Rightarrow 210Po\Rightarrow 206Tl\Rightarrow 206Pb$ (stable)

External links

http://enhs.umn.edu/hazards/hazardssite/radon/radonmeasure.html

• http://www.albert-cordova.com/lucas/lucascell.htm

• http://www.blackcatsystems.com/GM/articles/radon_thoron.html