Ya want to talk discuss radiation and granite, ya gotta learn the units used
June 5th, 2008
Boring stuff, but necessary, these units of radiation. Confusing, math required as well, but knowing the basics is the only way to keep up with the debate. I’ll keep it simple, leave out lots, and later you can fill in the gaps as you learn more about the issues.
First off, three things need to be measured:
1, The amount of radiation emitted. Activity
2. How much was absorbed by your body. Absorbed dose
3. How much damage did it do to your body. Dose equivalent
Some people like to use boxing as an analogy, how many punches were thrown, how many hit your body, and how much damaged did the landed punches cause.
Now it gets a little more complicated.
The rest of the world uses different units than we do in the USA and there are older units still found in some studies found on line.
The US uses Curie (Ci), Rad (r), Rem , and Roentgen (R). Uh oh, I mentioned four and we only had three to talk about. I’ll get to it.
The rest of the world uses Becquerel (Bq), Gray (Gy), and Sievert (Sv).
Curie measures the amount of radiation, same as a Becquerel.
1 Bq = 1 disintegration per second (dps) 1 Ci = 3.7 x 1010 dps 1 Ci = 3.7 x 1010 Bq
Rad measures the absorbed dose, same as Gray.
1 Gray = 100 Rad
Rem measures Dose Equivalent, same as Sieverts.
1 Sv = 100 rems
We will use the US units on this site for the most part, but sometimes the standard units are needed. Use the conversion factors above to convert into US units when needed.
Now what about Roentgen? That is a unit used to describe how much air is ionized by the radiation, which is how a Geiger counter works. So a result posted in Roentgens will pretty much tell you that it was a Geiger counter that measured the radiation.
But wait, some good news! For our discussion, we can figure that Rad, Rem, and Roentgen are roughly the same. Some particles like neutrons or Alpha are different, but for external exposure, we can assume Rad, Rem, and Roentgen are close to the same.
A Rem or a Sievert are very large quantities. We will need something smaller to discuss radiation. Standard math prefixes are used, most common are micro and Milli. A Milli is 1,000th of something. A micro is 1,000,000 of something. So a 1 Milli Rem (1 mR) is 1,000 times larger than 1 micro Rem (1 uR).
Now we have to add something, how long was the exposure? Usually hours or years are the units used, as in 1 mR/hr or 8,760 mR/yr. Remember that R can be thought of as Rem, Rad, or Roentgen.
If you have any questions, just post a comment and I’ll try to help.
Al
Once a granite has been tested, can all slabs of that type be considered safe?
June 5th, 2008
Think of the earths crust as a big mixer, or like a bunch of big mixers side by side. Some mixers will run longer, so the mixture might be pretty uniform. Other mixers might get bumped on once or twice, leaving little uniformity in the mix. Some mixers might have new ingredients added right before the end, resulting in veins or pockets of materials.
Granite can be uniform, but usually it isn’t. Some of the more uniform types are Absolute Black or Uba Tuba. These tend to test in a narrow range. But even within a single quarry, Uba Tuba will vary widely in color and quality, from quarry to quarry, the difference is even more pronounced.
Some granites are conglomerations, lots of movement and colors happening. These types of granite are the most unpredictable. I have seen slabs that test 15uR/hr on one spot, test 150 uR/hr on wide portions of the slab, then test 800 uR/hr on hot spots.
Currently, only a four or five hundred samples or so have been tested and reported worldwide. Some of the more comprehensive tests tested 80 stones or more, others tested a dozen or less. To my knowledge, no one but the SSA has ever tested multiple samples of the same type granite to find a range the stone usually tests in. So this science is in its infancy, too soon to say that any particular stone will always test safe.
To complicate things, the granite industry tends to be very fragmented. Sometimes a farmer opens a quarry, sells blocks to a processor that slices and polishes the slabs, then an importer buys the slabs and imports them, reselling to a slab yard or fabricator. In china, a licensed trader has to export the slabs, adding a another layer to the supply chain.
The importers, slab yards, and even the fabricators don’t want people shopping around on price, so they tend to use different names for the same stone. Called the name game, this can be a problem to consumers. You find a nice stone, but can find it in only one slab yard. Sometimes you can’t find any info at all on the Internet on your choice of stone. This becomes important for testing, who knows the real name of the stone so it can be tracked back to the quarry?
Plus, is there a chance that once a stone is know to test high radiation, nothing keeps the sellers from just changing the name so the stone can be sold. Our granite suppliers tell us that the stone industry is one of the most corrupt industry’s around. The going rate for bribing an inspector/agent is 4% of the value of the slab, so a $10 bribe will get a substandard slab left on the shipment instead of being rejected.
So, to be certain, we recommend that all slabs be tested prior to purchase. Our shop insists on this. It just makes sense given the expense of the projects.
