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This is an older study, but it is important because it shows that the issue of radiation in building materials has been brought up again and again over the years. Granted that in Europe this issue of radioactive building materials was dealt with with regulation, it still took some time to get it passed.
The following is a posting by Dan McCarn, an Uranium Geologist that has been helping with testing information and protocols. He provided a report on the Houston granite countertop lab analysis from ARS. The color coded chart is available, but as a spread sheet and will need to be converted into a pdf or Jpeg image for posting.
Dan travels the world working with Uranium mining companies and who would be better at avoiding high urainum levels in granite slabs than someone who has spent his life looking for Uranium? I would highly recomend him as a consultant to any stone company needing advice.
The following analysis was posted on the RadSafe site for an analysis for a piece of dimension stone. Al Gerhart submitted an analysis which contained some information (U-235, Ra-226) which I used to estimate the total U (Natural) of the stone. Note that this is a “high-graded” sample of a hot-spot. I do not know the methods used for the analysis, nor was it reported with the analysis.
“… a lab report on the countertop in Houston Texas that lead to this flurry of reports. It gave two Radium isotope contents as 1,130 pCi/g or so.
Potassium 40, 53.9 . (Potassium 40 is a radioactive element, the 53.9 is the amount in pCi/G)
Scandium 46 , 31.65
Cobalt 60 , .13
Cesium137 , .189
Thallium 208, 37.8
Lead 210 , 415.5
Bismuth 212 , 85.46
Bismuth 214 , 410.77
Lead 214, 484.99
Radium 226 , 986.95
Radium 228 , 128.34
Thorium 228 , 144.76
Uranium 235 , 37.83
ARS Houston Granite Countertop report
Assuming secular equilibrium between U-238 and U-234 (age of granite > 2 million years) and normal crustal abundance ratios of isotopes of uranium:
Isotopic Abundance (Solved for Secular Equilibrium Conditions)
Percent Weight Abundance
Activity at time t – Bq
Activity at time t – Ci
Activity at time t – pCi
Mass in micrograms
Mass in milligrams
Mass in Grams
Mass in Kg
% U (g/g)
Total activity is 1,680.30 pCi per 2.4610E+03 ug U-Nat uranium in secular equilibrium or
0.6828 pCi / ug U-Nat total activity
Ingrowth is essential to understand in order to interpret the meaning of the analyses. The sample would need to be canned for 30 days or so if crushed to achieve secular equilibrium with Bi-214. But, if I assume that the U-235 activity is 37.83 pCi / g given Al’s lab report,
1) the activity of U-238 should be 821.24 pCi/g, which is in rough equilibrium with Ra-226 (986.95 pCi/g) in Al’s report;
2) the total U-natural should be 2460.96 ug / g or about 0.25% U-Nat for the rock.
3) The Bi-214 value suggests that about 1/2 of the available radon has been emanated from the rock sample, but this might easily be effected by sample handling (crushed, ground, etc.) and not permitting enough time for ingrowth to occur in a sealed container. Since granites typically are in secular equilibrium, I suspect that sample handling is more at fault, but additional analyses would be required to confirm this.
The grade (0.25% U) would be enough to mine if commercial quantities actually showed this endowment, which I strongly doubt for a “plain” granite. However, leaching of uranium from such a zone of mineralization would be easily achieved in a wet, oxidizing environment assuming that the primary uranium minerals were uraninite or coffinite with no silica overgrowths. Petrographic examination of the rock would be necessary to determine this.
When granitic batholiths are intruded, the last remaining watery portions of the magma, having gone through differential precipitation (Bowen Reaction Series), is enriched in uranium and sometimes other metals e.g. tantalum, gold. These quartz-rich remainders can form intra-batholithic intrusions or peri-batholithic intrusions enriched in uranium. I suspect that Al’s rock may, in fact, be something of this nature. Attached is a colorized “image” (uR/Hr) of a four-seasons granite showing highly localized mineralization measured by Al.
I’d say that the only way would be in a vein within a granite, or a pegmatite, but not a granite itself, and the samples were “high-graded” to show a hot-spot, not representative of the overall composition of the granite. Of course what I’d call a pegmatite, and someone else may call granite from the dimension stone business, may be something of an issue!
For an “average” granite composed of 10 ppm U (e.g. Wyoming), the average activity would be 6.828 pCi/g.
For the Rossing anatectic alaskitic granite of 100 ppm U (0.01% U) in Namibia (active uranium mine):
The average activity would be 68.28 pCi/g
This is a message on one of the radiation enthusiast forums from a gentleman that I had sent some low level granite samples. Nothing over 60 uR/hr measured with our PM 1703 meters. He used aluminum shielding, so this is all Gamma radiation. Each “count” is a Gamma ray hitting the meter. His testing method is far more accurate than out hand held meters, showing that our meters are indeed catching a small percentage.
On the Bordeaux, our meters registering 40 uR, his machine measured 8,492, 21.2 times more.
The Niagara Gold was at 50 uR/hr, Steve measured 19,604, or 39.2 times more radiation.
The Four Seasons was at 30 uR/hr, Steve found 6,466, or 21.5 times more radiation.
No doubt that as the stone gets past 40 uR/hr on our PM 1703 meters, the readings become way low. The meters are still useful since anthing over 40 should not be sold under any circumstances. Steve measured background at 4,000 cpm wich is about 66.6 times our background levels, of course he no doubt had a different radiation level in Pennsylvania.
These readings roughly support one of our scientists measurements that say our meters are catching only 5% of the radiation. That would be 20 times more on the lower level granites, close to what Steve found.
Al & others
My measurements so far on some of the offending granites:
(all gamma counts are 30 second averages w/ background subtracted,
measured with a 2″ dia x 2″ h NaI(Tl) crystal 1/2″ from the polished
surface, with 1/8″ aluminum shielding.)
Bordeaux G-3 4/8/08:
8,492 cpm gamma
Silver-gray opaque mineral noted – several 1-2 mm grains – this is
probably the radioactive species
Niagra Gold N6 4/8/08
19,604 cpm gamma
~1 cm silver-gray opaque grain exposed on one cut surface + some smaller
grains – again, this is probably the radioactive species (I cut off this
edge and it shows higher cpm gamma than pieces without visible opaque
4 Seasons P9 4/8/08
6,466 cpm gamma
Fracture surfaces show greenish/colorless secondary U mineral –
fluoresces bright green under UV light, is clearly visible in daylight
but not visible under incandescent. Possibly autunite? Primary U
mineral(s) are almost certainly present in this granite but I haven’t
found any yet.
Is it possible to have Radon without Gama radiation being present?
I am not aware of any decay chain that doesn’t have ANY gamma, so it should be safe to say that No Gamma = No Radiation Since Radon comes from only two sources, Uranium 235 and Uranium 238, it should be impossible to have Radon with zero Gamma. If you wanted the short answer, stop reading here.
First the nonclamenture needs explaining for Electron Volts (eV).
K stands for Kilo, or 1,000, so KeV is 1,000 electron Volts.
M stands for Million eV, 1,000,000 electron Volts.
One thing to consider though, is there Gamma there that we can’t measure with hand held meters? Each meter, even each individual probe, will have a range of radiation energy (KeV to MeV levels) that it will measure. Higher or lower than this, and the meter won’t pick up THAT energy level radiation. But, look at this chart of Gamma levels in Uranium 238
Note that the levels run from 45 KeV to almost 1,800 KeV, which means that it is likely that SOME of the Gamma will be detected.
Now, look at the Gamma levels in Uranium 235
Note that the energy levels are lower, 27 KeV to 800 KeV, meaning that a detector that couldn’t detect lower than 827 KeV would miss much if not all of the Gamma radiation.
Now you have to look at the efficiencies of individual probes to see if they will indeed measure those levels. Look at the response curve (what levels it will measure) for the Ludlum model 19 probe
From 50 KeV to about 1,200 KeV gets detected, so the Model 19 probe will measure most (not anything below 50 KeV) of the U 235. However, since U 238 has some radiation above 1,200 KeV that won’t be detected with the Model 19 probe.
Then consider the PM 1703 we are using, response curve runs from 0.06 to 3.0 MeV, or 60 to 3,000,000 electron Volts. So a small amount of the U 235 and U 238 will go undetected, can’t get through the plastic case of the meter.
Lastly, there is the efficiency of the meter, or how much of the total radiation actually reads or registers on the meter. This is what Bill Llope is going to remind the experts about, that even the most expensive handheld meters catches very, very, little of the total radiation, as low as 2 to 3% of the total radiation emitted.
A good analogy would be a police car trying to catch speeding cars. Some he might be too slow to catch, some he can (Response Curve in KeV). On the other hand, he can catch only so many speeding cars per hour, leaving the vast majority of cars whizzing by uncaught (Efficiency of the meter).
Now, it is possible to have Thoron, another radioactive gas, present but the Thorium decay chain also has plenty of Gamma. So, no radiation, no Radon (or Thoron).
Here is our Youtube page with lots of videos on granite and radiation.
Some radioactive minerals glow under black light. This video was of the Four Seasons slab before it was cut up.
PM 1703 Scintillator picture
For measuring Gamma when surveying granite countertop slabs or existing countertops, we use a PM 1703 Scintillator. When a Gamma ray hits the crystal inside the meter, it causes a flash of light, which is measured by a photodiode, then counted by the electronics. We will cover basic operation of the meter in this article.
In the picture, there are two grey buttons, top and botom. The top button is the mode button. If the meter is reading “off” when you get it, just hold the top button down for a few seconds and it will start up. If you have recieved a brand new meter, just insert the battery. Look for the large honking screw on the side of the case.
Once it comes on, the unit will test itself, then it will calibrate itself to background radiation. Takes a minute for both to happen. If the meter doesn’t pass the test, it won’t start the callibration process.
At this point, you are ready to go to work. Just hold the meter in contact with what you want to test. If you move the meter slowly, you can scan an item. Move too fast, and it won’t read accurately. One foot of travel per three or four seconds will do for a rough survey.
The lower button turns on a light for the screen, allows you to turn the unit on and off, and allows the unit to communicate with a computer to download info or upload info.
The beeper can be turned off, so can the vibrate alert. I recomend turning off the beeper if you are surveying in a slab yard or stone showroom, annoying as hell, and you will scare people.
To turn the beeper and vibrate on and off, hold down the top button, the mode button, for a few seconds, maybe six seconds. At first it will say “cal” for calibration, keep the buttom pressed down. After five or six seconds, it will display a “n 5.5″ or something close. That is the alarm level, set at 5.5 ratio (why the meter re callibrates each time you turn it on). punching the lower button will cause the “n5.5″ to flash on and off.
When it does that, punching the bottom or top button will make the “5.5″ go up or down. play with it, set it where you wish, then do nothing. The meter will reset itself with the new level of alarm.
It is recomended to leave it at 5.5, set it on one and the meter will beep a lot. Set it at 9.9, and it will read fine, but the alarm won’t warn you when the radiation level shoots up high.
Now do that again, but this time when the “n5.5″ is displayed, punch the top button. Now the meter shoud read “1-on”. Punching the lower button toggles the on and off function. #1 is the beeper, #2 is the vibrator.
If you do nothing after that, the meter will reset.
After setting the “1″ to on or off, punch the top button and it should display “2-on”. Same procedure if you want to turn that function on or off. Pretty simple.
The meter reads in micro Roentgens per hour. You now have the data to make a decision, what normal background radiation is, and how hot the granite is.
Now we enter unknown territory. Two camps, but the overwhelming consensus is that ALARA, As Low As Readily Attainable, is the standard. Sure there is a camp that believes in Hormesis, a fringe theory that says radiation is good for you….. We will stick to facts here.
To turn the meter off, hold down the lower button (the light button) for a second, then while still holding the light button down, depress and hold the top button for a few seconds till “off” appears on the screen.
Please don’t drop the meter. It has a crystal inside that can be broken.
This meter retails for over $1.200, but they can be found one place cheaper, for $383.28 with shipping. The SSA has arranged a group rate if we buy in multiple units, you would save shipping, and the SSA gets a small percentage. Any money raised will be earmarked for technical equipment for testing. Units will be shipped in lots to us, the meters will be tested, then reshipped to the owner. You are saving $13.00, and someone knowlegable and neutral has made sure it is working fine. We will pay the shipping going out.
Florida state has recently evaluated several residential units in high-rise buildings in south Florida to find the source of the Radon in the structures. Since soil based Radon usually is cut in half for each story upward, finding Radon in twenty story condos was a surprise.
As part of their search, they recorded the gamma spectra of the radiation emanating from various building materials including granite counter tops. That data is still under evaluation and they are still developing the techniques to interpret it. The evaluation should be complete by the end of August.
Other buildings have been studied and the concrete found to be the culprit. In one unit, it was a concrete ceiling that contributed the lions share of the Radon.
Once the information has been released, we will share the results.
There has been some concern on the Garden Web forum about Bordeaux granites, which ones tend to be high level and which ones tend to be low level. I thought I would share what I have found so far in both informal testing and what little professional testing done so far.
To put things in perspective 10 uR/hr reading at some state recycling centers will be reported to the state radiation control office. Other states like Kansas, allow 25 uR/hr over background radiation (typically 6 to 8 in our area), so a 31 to 33 uR/hr scrap metal will cause alarm. Uranium processing plants being decommissioned must clean the soil till it reaches 5 uR/hr, average radiation level for soil.
Personally, from the last few years research, I set a level of 25 uR/hr over background for the slabs I am willing to let my workers fabricate.
Juparana Bordeaux, shortened to Bordeaux, is one of the ones that MUST be tested prior to purchase. Rarely do you see a Bordeaux below 50 uR/hr Gamma. Much is at 75 to 100 uR/hr. That doesn’t mean you won’t find a low level slab if you go through enough of them.
Crema Bordeaux is one of the lower level Bordeaux. We have tested 5 slabs so far, using the LENi Geiger counter. From 240 to 1500 uR/hr counting Alpha, Beta, Gamma. The fact that there are 240 uR/hr slabs out there shows that one can find lower level slabs. Counting Gamma only, Crema Bordeauxs can run as low as 25 uR/hr, right at our cut off level for safe slabs. Crema Bordeaux did test rather high in the MIA sponsored tests, 292 times more than some of the others, so a Radon detector is a good idea. States sometimes offer them at great deals.
We found one Bordeaux, Golden Bordeaux, that was quite low, 13 uR/hr. Only one slab available for testing, so it doesn’t represent a range, but it is worth looking into if you have your heart set on a Bordeaux.
To put things in perspective on Bordeaux, though, consider the test results on the Houston slab, done by American Radiation Services International . Here is a list of the elements causing it’s radiation.
Potassium 40, 53.9 .
Scandium 46 , 31.65
Colbalt 60 , .13
Caesium137 , .189
Thallium 208, 37.8
Lead 210 , 415.5
Bismuth 212 , 85.46
Bismuth 214 , 410.77
Lead 214, 484.99
Radium 226 , 986.95
Radium 228 , 128.34
Thorium 228 , 144.76
Uranium 235 , 37.83
Total 2,670.196 pCi/g or if you want to compare it in uR/hr, multiply by .95, or 2,337.088 uR/hr.
That slab, in addition to its radiation, one should consider its heavy metal content and the health risks if any.
Potassium is quite harmless, both chemically and it’s decay chain products. It does react with water though, so keeping a granite top dry is always a good idea. The number one reported repair to granite is waterdamage around sinks, according to two companies that repair all types of tops.
Scandium doesn’t seem to have any health effects.
Cobalt 60, yes that Cobalt 60, is another story. Luckily, in this case, the amount in the granite was pretty low. It does produce a dust that is a problem for radiation control. Cobalt 60 has an afinity for Arsenic, another commonly found element in granite, so don’t use granite as a cutting board, don’t roll dough on it.
Caesium is used in atomic clocks, mildly toxic for our discussion because it replaces potassium used in bodily functions.
Thallium is highly toxic, once used in rat poison and insecticides, but banned in the US in 1975. Thallium is also highly water soluable and readily absorbed through the skin. Again it is very close to potassium and can be taken up in the body’s potassium uptake pathways. Thallium has been used as a poisioning agent in murders, although an antidote, Prussian Blue, is available.
Lead needs little explanation, it is a neurotoxin that accumulates in soft tissue and bones.
Radium is taken up by the body as calcium, depositing in the bones and destroying bone marrow. It is a major source of the Gamma radiation in granite.
Thorium produces Thoron gas, which like Radon can decay inside the lungs. Ingestion is the biggest hazard, so again don’t use granite countertops as cutting boards or dough rolling surfaces.
Uranium is both water soluble and acidic liquid soluble, so acidic foods and liquids need to be cleaned up carefully off granite. Uranium is a toxic metal, has been linked to birth defects. Once in the body, it tends to bioaccumulate. Breathing the dust another hazard, of course the Radon that decays out of it is a hazard as well.
The complete lab report on the Juparana Bordeaux granite countertop can be found at the SolidSurfacealliance.org website