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Author Topic: Can clay absorb a dangerous level of radiation?  (Read 4554 times)

Offline thedoc

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Can clay absorb a dangerous level of radiation?
« on: 10/10/2012 05:30:02 »
Maty P. Thompson asked the Naked Scientists:
   Bentonite clays are know to absorp radiation and hold it. If a clay has 140-150 CMP would it still be safe for human use?
What do you think?
« Last Edit: 10/10/2012 05:30:02 by _system »


 

Offline SeanB

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Re: Can clay absorb a dangerous level of radiation?
« Reply #1 on: 11/10/2012 19:48:16 »
Clays hold many heavy metals, but not radiation. They can be used to immobilise radioactive materials which will stay fixed in the clay, and depending on the particular radioisotope it will be elevated for a long time.
 

Offline Bored chemist

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Re: Can clay absorb a dangerous level of radiation?
« Reply #2 on: 11/10/2012 20:58:32 »
There's not enough information to answer the question.

(Incidentally, do you mean CPM?)
 

Offline Mazurka

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Re: Can clay absorb a dangerous level of radiation?
« Reply #3 on: 12/10/2012 14:10:33 »
Bentonite clays are a fascinating group of minerals.

(To use the common but less than 100% technically accurate description) Calcium Bentonites are used by some alternative/ complementary practitioners for treating digestive aliments and “detox” programmes and there are several places on the internet where suitable bentonite can be purchased. Other mixtures of clay minerals (including stuff like Fullers earth) have been used historically and are occasionally used today for treating certain types of poisoning.  It is the adsorptive properties of clay minerals that lead to their use and they can be used to adsorb radionuclides to allow removal.  However, why you would wish to consume irradiated clay at any count rate is beyond me.


For medicinal / detox purposes it is often referred to as “organic bentonite” (despite being an aluminium silicate derived from weathered volcanic ash and (notwithstanding the hydrogen in water) having no carbon or hydrogen in its structure) 

It is important that the right bentonite is used – sodium montmorillonite (bentonite) – commonly used as an engineering material adsorbs water to an incredible extent and could potentially be very harmful if ingested.  People handling  sodium bentonite powder are recommended to wear eye protection and face masks.
 

Offline Bored chemist

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Re: Can clay absorb a dangerous level of radiation?
« Reply #4 on: 12/10/2012 18:14:41 »
Any bentonite  with potassium in (and I guess they will all have some) will be radioactive.
 

Offline Boogie

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Re: Can clay absorb a dangerous level of radiation?
« Reply #5 on: 17/10/2012 21:22:30 »
There's not enough information to answer the question.

(Incidentally, do you mean CPM?)

I agree.

CPM does not describe the activity or radioactive exposure from a source.

In order to calculate the activity, you need to know the efficiency of the detector for a particular isotope, as well as background counts and source counts.

Let's say, for example, your detector has an efficiency of 12% towards Cs-137. Let's also say that the background counts (without the source) is 60 CPM and counts with a Cs-137 source is 150 CPM.

First, convert CPM to CPS
60 CPM / 60 sec = 1 CPS
150 CPM / 60 sec = 2.5 CPS

Activity (nCi) = (Source CPS - Background CPS)/((efficiency/100) *37)
Activity (nCi) = (2.5 - 1)/((12/100)*37)
Activity (nCi) = 1.5/4.44
Activity (nCi) = .338 nCi

Back to the clay :

Measureing and calculating the activity of Bentonite seems difficult to me since K-bentonite contains Potassium which is radioactive and also absorbs radiation from other isotopes. If you didn't know what isotope was the source of the radiation absorbed by the clay, it would not be possible to calculate the activity with a CPM instrument would it? Conversly, if you knew, for example, that the isotope that produced the radiation absorbed by the clay was Cs-137, then could it be possible to calculate the activity of the clay with a CPM instrument or does the mixed isotopes confound the whole process? I'm Not sure how you would go about calculating the activity or exposure from the clay. I think you would need to use an energy compensated survey meter, yes?

By the way, calculating detector efficiency is easy if you have a source of known activity.

The following formula assumes that a 2pi geomotry is used for source placement (point source directly on the detector)

Det Efficiency (%) = ((source CPS - Background CPS)/((37 x activity of known source in nCi)/2) x 100

Let's say, for example, we have a 9.253 nCi Cs-137 source and we know that background counts are 120 CPS and counts from the Cs-137 is 150 CPS with the source directly on the detector.

Det Efficiency = 150-120/((37*9.253)/2)x100

Det Efficiency = 17.525% for Cs-137

If I made error, please set me straight as I'm still learning.

Edit : I didn't see SeanB's post about the clay trapping the radiation that it absorbs, until after posting this, so please disregard my questions about the clay (above).
« Last Edit: 18/10/2012 02:25:09 by Boogie »
 

Offline BioChemSFC

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Re: Can clay absorb a dangerous level of radiation?
« Reply #6 on: 18/10/2012 00:26:39 »
The ability to absorb radiation (I assume gamma) is directly proportional to the density of the material and size of nucleus(yes they are related). This is why lead is used. Cement is used to block gamma radiation but you need a heck of a lot. I am sure clay would work but would but only in large amounts. Fallout shelters are built with 3+ feet of concrete. So it would work but seems unpractical because you cannot pour it. The other people seem to make it a lot more complicated(still in school?) but thats the answer. 
 

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Re: Can clay absorb a dangerous level of radiation?
« Reply #6 on: 18/10/2012 00:26:39 »

 

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