First background radiation levels are recorded before measuring, as well as afterward. That level is subtracted from the total.
Same thing with Radon. For example, we found .775 pCi/L of Radon in our Radon room prior to starting the last round of testing. After 18 square feet of some fairly hot granite was installed, the room Radon levels went over 10 pCi/L. Later another 18 square feet of the same granite was installed, but this additional granite was low radiation level. We expected a ten to twenty percent rise in Radon levels.
Instead it first doubled, then trippled. The reality is that not only is the radiation level important, but the porosity that allows the Radon to escape.
A later test with all the hot granite was removed and replaced with low radiation level granite. That test averaged around 20 pCi/L.
Another point is that our testing verified what four Radon researchers predicted from their lab testing.
We are about to start testing again with variable ventilation to see exactly how much air flow it takes to lower the Radon levels. We know that with an open door, the room stays around 2 to 5 pCi/L.
Look in the 2008 symposium papers. Brodhead has two papers that cover his findings and Kitto has one. Note that Kitto’s paper isn’t the complete presentation he gave at the conference. He had a study ready, but some of the seriously hot granite samples we sent convinced him to reopen his research. It is finished and going through peer review. It will show up to 24 pCi/L radon in an unventilated room, half that for normal ventilation.
This September, there will likely be a panel discussion on the issue again. ARRST asked me to participate and to line up the other speakers. Dr. Steck and Dr. Kitto have agreed so far, along with an Industrial Hygienist who also is a certified Radon tester in CA. A very respected Physicist has accepted but is awaiting approval by his employer. I asked the stone industry to participate as well.
Some reds are a problem, most aren’t. The hottest stone found so far is a black and white slab. Red dragon for example is safe as can be from the slabs we’ve tested so far.