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Radiation from Granite: A Definitive Explanation

The “Straight Goods” On The “Radioactive Granite” Issue:

An Interview with Professor William Llope, PhD; Rice University, Houston, TX

Connor Ferster, Universal Slate: Hi Professor Llope, I am a salesman at a Canadian stone import company called Universal Slate Int’l and wanted to provide my interior designer clients with some legitimate ‘hard-and-fast’ information regarding the potential dangers of radon gas in granite counter-tops.

Professor William Llope: I very much appreciate that you are taking this with an open mind. There are some that claim that this is a “myth” or that this story is simply industrial subterfuge (re: granite vs “synthetic” countertop options). To be clear, I have no affiliation whatsoever with the granite industry, any competitors to granite, granite testing agencies, or any entity like this with some stake in this game. I am completely independent here, and am paying for this research out of my own pocket simply because I find it interesting. Now, the bottom line here is that, on average, the vast majority of granites are safe. This much is clear. But to say that *all* are perfectly safe is a more sweeping comment, and is one that I believe cannot be supported by experimental data.

The issue: Types of radiation

Connor Ferster: I found your name in reference to studies being done at Rice University on radon off-gassing in granite counter-tops in the The New York Times article, “What’s Lurking In Your Countertop?” (July 24, 2008). The article stated that you were conducting studies on granite widely used in kitchen counter-tops, presumably on levels of radon gas emitted by such granites. You have also appeared on The Today Show on MSNBC in 2008 as an expert on this subject.

Professor Llope: Actually I’m concentrating on the direct radiation, although the radon emanation and the direct gamma radiation are typically correlated in the hottest stones. The (relatively rare) stones that are very hot in terms of the gamma radiation are typically relatively very hot because they contain elevated amounts of uranium ore or thorium-232. These admixtures of uranium or thorium can result in the emission of radon or thoron gas *and* gamma radiation.

The dangers of radiation

Connor Ferster: It seems that a lot of the press that I have read focusses more on the radon gas emissions and not direct gamma radiation. Would you say that one or the other is more of a concern? Can you give me an idea of the different dangers each one would pose and why?

Professor Llope: You have to distinguish between the radon emanation rate and the direct gamma emission rate; in the hottest stones, both can exist.

The radon is measured in terms of a concentration in air in units of pCi/L (picoCuries/Litre) – a la the 2-4 pCi/L EPA limits. Radon exposure is a risk to the lungs from inhaling radon-laden gas. You take in a breath, and during that breath, radon nuclei decay which shoots alpha particles into the soft tissue of your lungs. Over years, this can result in big damage, and in fact radon exposure is the second leading cause of lung cancer.

This same radon gas flowing around the outside of your body emits the same alpha particles, but these cannot pass through the dead layer of your skin called the epidermis. No damage.

On the other hand, the gamma and beta radiation that some emit in significant quantities are a “whole body dose”. Your whole body is getting splashed with radiation. Much of it passes right through you. But some of it interacts inside you and hence deposits energy in cells, which can damage the cells and DNA and potentially lead to mutations (cancer).

This distinction between the health risks from radon and direct radiation is a huge source of confusion in the public.

The important thing to remember is that mitigation for radon involves air exchanges. i.e. open windows or forced ventilation of some kind. That exchanges radon-laden air (from one’s basement or, in rare cases, their granite counter tops) with air from outside, which may have less radon in it.

There is no simple mitigation strategy if the counter tops are emitting significant quantities of direct radiation. Those gammas (and betas as well) are shining off the counters and can travel several 10’s of feet before ranging out. The only mitigation there is to cover your counters with 6 inches of lead, or to limit the amount of time you spend in the kitchen. Neither are particularly attractive options obviously…

Debunking “the myths”

Connor Ferster: Through my own internet ‘research’ I’ve found what seems to be a lot of “pseudo-science” on the topic (’radioactive potatoes’, etc.). My assumption from these videos would be that since all of these every day items emit radiation, the actual danger of radiation from granite is over-hyped. Can you comment on this?

Professor Llope: Radioactive potatoes, bananas, brazil nuts, etc are not “psuedoscience”. These things do emit radiation in measurable quantities. I have taken “textbook” spectra from bananas for example. The data I get looks exactly like a Potassium-40 source should.

But, one needs a sense of scale. There is a natural background to the radiation that we receive every year, and foods like these *do* contribute to this natural background. We also receive natural background radiation from cosmic rays, from other building materials, from medical and dental x-rays, from radon from the ground in many locations, and so on. All of these sources are “known” and understood to be part of the natural radiation dose that we all receive every day of our lives. These sources are a fact of life on this planet.

This natural background level (360 mrem/year) varies by factors of 2-3 depending on one’s location and lifestyle. Again, this is also well known. An airline pilot flying from New York to Los Angeles will accumulate an additional ~4 mrem, per trip, of absorbed radiation just from cosmic rays.

But, what we are talking about here are specific stones that can emit radiation at rates in “hotspots” that are factors of some *hundreds* above this natural background level. I have many stones for which there are large areas that emit radiation at rates that are ~10 times or more above that from the natural background.

Comparing these stones to bananas or potatoes is thus somewhat misleading. There are hugely different scales in the two cases. Yes, both emit radiation, but to say that both can emit radiation at similar rates is not always true for specific stones. This is not to mention that one does not have *hundreds* of square feet of bananas surrounding them in their kitchens, like they do with their countertops. Again though, I need to stress that it is a relatively small fraction of the decorative stone out there that are very hot like this. The majority are quite quiet and emit radiation at rates that is a small fraction of the natural background. This majority should thus be considered “safe” in general.

Radon gas vs. Direct gamma rays

Connor Ferster: Given what you’ve told me, I can see how radon gas could be less of a threat to health and safety given the variety of mitigation methods available. I can also see how much more of a concern having direct gamma radiation would be for a consumer.

Professor Llope: I wouldn’t really try to say one is more important than another. One at least needs to recognize that radon alone is not the whole story, nor is the radiation alone. I wouldn’t want to see a prioritization of the concerns here just yet. At this point what consumers need is the straight facts on what is going on. Both issues “exist” however the relative importance of each depends on a whole lot of other factors and thus it will always be difficult to come up with some general rules that consumers can understand re: predicting whether the radiation or the radon or both is a concern for them.

“The Key Question”

Connor Ferster: Now, getting into the crux of the issue, with some of the hottest granites you have tested, what would you estimate would be the total absorbed radiation in mrem (in a month) if someone were to be touching the hot spot for 1 hour/day? I just want to get an idea of the scale of radiation absorption that could be possible with a hot granite in a residential setting. Would it be below the acceptable additional dosage of 100mrem above and beyond the normal 360mrem from background radiation?

Professor Llope: This *is* the key question! To answer it directly though, I’d be giving away the major result of the paper that I’m working on, and I don’t want “to publish in a blog” – I hope you understand. Suffice it to say that there is indeed a non-zero correlation between the readings given by a geiger counter at the surface of the stone and the total absorbed dose of someone standing in a kitchen for a few hours a day… i.e. There is an effect here, and indeed a calculable dose that can be correlated with Geiger counter readings on the surface of the stone.

Proper detection measures

Connor Ferster: I was reading on your FAQ that a geiger counter, while it CAN be used to properly get a measure of the absolute amount of gamma radiation emitted from a sample, cannot be relied on (on its own) for a truly accurate measurement of absolute gamma levels.

Professor Llope: Correct. Geigers are 100% efficient (roughly) for beta particles because they are charged particles, but are only a few percent efficient for gammas. The Uranium ore and Thorium-232 in the hotter stones are primarily gamma emitters.

Connor Ferster: You mention to use a detector with a ‘2″ or 3″ deep NaI(Th) crystal’, instead. What is this kind of detector specifically called?

Professor Llope: It’s a detector with a Thallium-doped Sodium Iodide crystal. Basically, it is a 3″ diameter by 3″ depth crystal attached to a light detector called a photomultiplier tube. It is much more dense than a geiger counter so it has a much larger absolute efficiency for measuring gammas. This larger absolute efficiency means that it sees much closer to the total number of radiated particles than does a geiger counter.

Also, as opposed to a geiger counter (which just “counts”), the NaI crystal is “energy-resolved”. i.e. I can collect an “energy spectrum” from each of my samples. These spectra have peaks in them that correspond to specific nuclear decays in the stone. I can thus measure directly how much 40-Potassium, Uranium ore, and 232-Thorium are in each stone. The energy resolution of NaI crystals is not spectacular, but it is good enough to determine how much of each of these three major decay series are in the stone.

Additional information sources

Connor Ferster: Whilst I am working in the stone industry, I don’t feel like I can *entirely* trust information coming from the Marble Institute of America. I would much rather speak to an independent source. I don’t think my customers would really trust me if I was just taking information from the Marble Institute of America, either.

Professor Llope: The more you know, the better prepared you will be to handle a customer’s concerns. If you can give them well-informed answers, they will be more likely to do business with you. I can tell you that i have answered several thousand emails on this subject over the last year-plus. I always recommend simply asking the dealer for his/her opinions or their data, if available. If I’ve been told a dealer got upset by the question, or swept it under the rug as a “myth” or “junk science”, I suggest to the consumer that they choose a more-informed dealer.I do not, in general, steer them away from granite. I simply steer them towards dealers that are willing to help consumers pick stones that *both* attractive and quiet. Again, the dangerous stones are relatively rare. The vast majority of trade names should be considered safe, all things considered. Just not *all* stones.
If people would like more information on this topic, then people can visit my FAQ on the issue.

Connor Ferster: Thanks for your time, Professor Llope! Please let us know when your study is published and we will link to it from here.

Professor Llope: The pleasure is mine. Thank you for the interesting discussion. Take care

Limestone and Marble Staining – Part Two!

Last week we uploaded a video showing how limestone and marble were resilient to stains caused by common bathroom staining agents.  This week we did a video showing how limestone and marble are resilient to stains caused by various foods found in the kitchen.

Like last week, the stones were sealed with Miracle Sealants’ 511 Impregnator.

A quick synopsis of the results: while we found that none of the stones were stained by anything, there was some mild etching caused by the acidic items we were testing, namely ketchup and balsamic vinegar.  So, while there is no danger of any staining you do want to wipe up any acidic fluids shortly after they are spilled. (Maybe I’ll do a video showing how easy it is to remove etching from honed surfaces…)

Anyways, enjoy!  I realized after I uploaded the video to YouTube that the audio is slightly off-sync with the video, so, bear with it.

Limestone and Marble Staining, Exposed!

Ever since I’ve been working at Universal Slate, people have been telling me that “they heard” that limestone and marble shouldn’t be used in a bathroom because “it’s so porous and stains easily”.

But, is it true?  Watch the video below for some surprising results that may change the way you work with marble and limestone.

P.S. This is my first video and I learned a thing or two through the process.  At the beginning there is a lot of background noise but it goes away after a minute or so.

New mosaics (and colossal tiles) coming in to Universal Slate

After a rough year in 2009, we are finally getting back on our feet and focusing on bringing new material.  Our next container from Turkey (estimated to arrive in December) will have three new mosaic tiles and a new stone colour for us.  We have samples of the mosaics, see below, and so we are able to take some halfway decent pictures of them.  For the new stone colour, Silver (vein cut), we only have photos provided by the quarry and photos supplied by quarries are notoriously bad.  So, while I have included it in the photos below, I’ll be hopefully be getting a sample shortly to take some of our own photos.

Click the thumbnails below for larger resolution photos.

These are the three new mosaics we have coming in December.

These are the three new mosaics we have coming in December.

Cartagena Ivory/Noce blend (1"x1" squares; 12"x12" sheet)

Cartagena Ivory/Noce blend (1"x1" Squares; 12"x12" Sheet)

Cartagena Ivory (1"x1" Squares; 12"x12" Sheet)

Cartagena Ivory (1"x1" Squares; 12"x12" Sheet)

Umayo (Split-face Dolomite with Jet Black dots); 12"x12" Sheet

Umayo (Split-face Dolomite with Jet Black dots); 12"x12" Sheet

Now, Silver (vein cut) is going to be most similar to our existing Ocean Blue which is a grey Italian travertine that we stock in 12″x36″.  The differences between them is that Silver will be darker and will have a “curvier” vein flow.  Initially, we wanted to get Silver in to supplement our Ocean Blue as we’ve been finding that the Ocean Blue has been coming in more creamy looking.  With the cream in there, Ocean Blue has been looking more ‘greenish’ and not quite as sharp as we’ve seen in the past.  We’ve checked with the quarry on this and it seems that all the Ocean Blue they’ve been shipping out is looking like this.  I even cross referenced with Stone Tile West since we have those products produced at the same quarry; theirs is look exactly the same.

So, we wanted to get Silver in a 12″x36″ to perhaps go along side our Ocean Blue as an alternative but we couldn’t get it produced in that size.  Instead we got something much better!…

Our Silver (vein cut) is going to be coming in as an 18″x36″ tile!

We’ve only ever stocked 18″x36″ tile once in the past and that was the Morocco Beige, a rather plain looking stone.  It sold out within weeks.  Unfortunately, at the time, we didn’t have enough room to make it a regular addition to our inventory.  Now, we have room and will be starting to regularly stock this incredible size!

This is indeed a rare size and is something not typically available within Canada.  We have only 2000 Sq Ft. coming in for the first order so if this is something that you are interested in working with, drop me a line and let me know so I can try and reserve a sample for you.  Plus, this 18″x36″ stone is going to be completely affordable. Even though I don’t have a final pricing on it yet, our preliminary costings are looking very promising for the Silver (vein cut) to be an affordable stone option.

Silver (vein cut); Shown here as a 12"x24" tile, stacked.

Silver (vein cut); Shown here as a 12"x24" tile, stacked.

Slab Shower photos

Last week we had the glass installed on our newly built slab shower in the showroom.  We built it out of 3/4″ Bianco Antico granite and 10mm glass walls and includes a niche on the left-hand wall.  The cost on a shower like this, including $2500 in glass, would be about $7500.

Click the photos for a larger view.

Bianco Antico Slab Shower

This is our new slab shower. It measures 4'x4' and stands about 8' tall. The door is on the right-hand side.

4'x4' Slab Shower doorway

This is from the doorway looking into the shower. Notice the continuous vein running from the slab on the right, through to the slab on the left (in the lower right-hand corner), and on to the base.

This is the sand-blasted slab shower base.

This is the sand-blasted slab shower base. The texture is pronounced enough to ensure that there is NO chance of somebody accidentally slipping on it.

Website Troubles

We currently have no idea why but our website seems to be in-operative.  We are in the middle of fixing and will post when it’s back on line.  We are anticipating by the end of the week it should be back up.

If you have any questions or sample requests during that time, please just email Connor Ferster at connor@universalslate.com.

Thanks for bearing with us!