One more idea on radioactive countertops: Several ideas, actually,

I have tested a number of different stone counter materials in an informal way, and none were hot. However, I have direct knowledge of one that was quite hot, detected by a CRM moved to the counter after the basement test was done, but not turned off. (long story, realtor involved). It's pretty clear that some stone is radioactive, most is not. So if it's your house, or your family's house, the obvious answer is to test. Test the basement, test the bedroom, test the kitchen, test the air right on the counter or stone floor or stone shower enclosure. Passive tests are really cheap, nearly free from many county health departments. Deploy a half dozen of them at the same time, and have fun interpreting the results

I agree, not all granite is hot. The Chinese have done more testing than other countries, indeed the law requires all granite be tested before bringing to market. They have a sticker, not unlike our Matteress tags that must follow the slab till it is installed. The Chinese say that between 30 and 20% of all stones fail the Class A rating (.3 mSv,yr exposure or 41 uR/hr gamma). What testing I have done shows around 3 to 5% of granite is of major concern, if you consider types of granite.

In a real estate transaction, active tests are more likely to be in use, and are much more expensive. Not likely you could talk a client into multiple tests. I've done a few that way at the customer's request, one CRM in the basement, one in the kitchen, and my customers were glad to know that their stone wasn't hot.

We are using Scintillators to indicate Gamma, not really looking for Radon. I think that is best left to the professionals. A Scintillator will tell you from 8 feet away if there is a problem..

The comment by the manufacturer association about the equilibrium ratio, and the half life calculated to the ten-thousandth of a day was amusing. Does anybody know what it means?

I can speak to the Equilibrium Ratio. Not sure I understand the nuances of it yet, but apparently the Radon at some point reaches max level because it is decaying into daughter products as fast as it is being produced, or that seems to be the gist of it. I have heard that around 21 or 27 days. Dr. Llope said to just open your windows for a half day every three weeks to prevent the Radon building up to the max levels.

I didn't find the half life calculated to ten-thousandths, what page was it on?

When assessing cancer risk, it's the lifetime dose that counts, not the instantaneous exposure to any one source. So the problem with stone is its contribution to the overall house radon level. (Same as with radon in water.) However, if you have an unacceptable radon level in the home, it would be really good to know where it's coming from, so you don't waste time, effort and money mitigating the wrong place. That's the only good reason for multiple tests.



Matt Bezanson, NEHA RMP101003RT, NRSB RMS # SS75