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 Low reading on new GMC-300		  New Topic  Reply to Topic
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dcdyd

USA
3 Posts
Posted - 04/28/2012 :  09:21:12  Show Profile  Reply with Quote
Just brought new GMC-300 from eBay for measureing the radiation level of Granite counter top due to the concern of the potential high radiation level seen on Internet.

Played with it today in house and the reading seems to be low. The average disposure of US resident to the radiation from nature source is said to be 300mRem per year. CHange it to hour, it is 0.034mRem/hour. However whenI used it in-house, it displays about 0.01mRem/hour.

Does it sound right? Is any calibration we need to do for correct measurement?
Reply #1

ZLM

1261 Posts
Posted - 04/29/2012 :  17:35:20  Show Profile  Reply with Quote
It sounds OK to me.

All locations are different. The only thing we can see is that your location is very safe.
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Reply #2

horseflesh

3 Posts
Posted - 04/30/2012 :  20:36:11  Show Profile  Reply with Quote
What CPM are you reading? I haven't bothered with Rem/Sv so I don't have those values on hand.

Here in Seattle I have about 10-20 CPM from background.

A stack of ceramic plates reads 30 CPM.

An old radium watch reads 1100 CPM. (Cool!)

A granite boulder in a park did not read above background. Things are different all over.

I would NOT worry about exposure from a granite countertop. Even if you detected something from your countertop, it'd be below background levels for someone in a different part of the world.

You're probably at much more risk from radon gas accumulation if you have a basement.
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Reply #3

ZLM

1261 Posts
Posted - 04/30/2012 :  23:11:47  Show Profile  Reply with Quote
10-20 CPM from background is a very good reading. It is in a normal range.
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Reply #4

dcdyd

USA
3 Posts
Posted - 05/01/2012 :  10:33:34  Show Profile  Reply with Quote
My CPM reading is about 10-20 in most area of the house and 20-30 when placed on a piece of granite sample. Probably both reading are within the normal range.

My concern comes from articles on the internet which talks about potential high radiation level from a particular granite pattern from Brazil. I understand that all granite produces some level of radiation but in most cases those are still small and is not harmful to human body. However this particular granite stone was said to have the highest radiation level. But it is beautiful and matches our kicken. That is the reason I opurchase this device and I will go to the show room of the fablicator this Friday for taking a measurement.

I really hope that the test result is good. Otherwise we will have to find different granite stones.
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Reply #5

ZLM

1261 Posts
Posted - 05/01/2012 :  11:08:38  Show Profile  Reply with Quote
20-30 CPM in a normal range. I think the healthy level from GMC-300 should less than 100 CPM.
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Reply #6

NRFneversail

USA
22 Posts
Posted - 05/27/2012 :  22:34:56  Show Profile  Reply with Quote
I recently was about 200 miles away as the Crow flies from where I'm at here in Idaho to another location in Idaho. The elevation here is about 1650 feet above Sea Level but in one of the deepest canyons in the US and the other back home about 5472 feet elevation in a high desert valley surrounded by mountains up to another mile higher. My average CPM (both indoor averages over several hours)here can be about 6.40 CPM and back home about 8.22 CPM. Back home is higher in elevation plus is not much of 20-30 miles from a Nuclear Reservation though I attribute the small increase to elevation and maybe geology. The GM Tube I have in my GMC-080 is an Anton/Navy 6107 so is made for Alpha/Betta particle and Gamma ray detection. Having been a former Radiation Worker back home, I consider these CPM's to be about normal. I've even taken cotton swab or paper swipes of outdoor surfaces and exposed them to the Alpha/Betta window to see if I can find a Hot Particle from any Fallout and no luck yet.

quote:
Originally posted by dcdyd

Just brought new GMC-300 from eBay for measureing the radiation level of Granite counter top due to the concern of the potential high radiation level seen on Internet.

Played with it today in house and the reading seems to be low. The average disposure of US resident to the radiation from nature source is said to be 300mRem per year. CHange it to hour, it is 0.034mRem/hour. However whenI used it in-house, it displays about 0.01mRem/hour.

Does it sound right? Is any calibration we need to do for correct measurement?
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