RE: soil samples

["Neil, David M" <neildm@ID.DOE.GOV>]

When I was involved in such, it was done with a GeLi, but it was a MUCH

larger aliquot of an even larger sample.  The aliquot was a 500 ml jar full,

say 750 grams+- out of around 1500 grams of raw sample.



I don't have information on detected levels and detection limits, as I was

collecting and preparing, but not analysing.



I would try real hard to get some sort of reference sample of similar soil

composition, since, as you said, everything you saw was expected.  I would

expect Cs137 as well, from historical fallout.



Dave Neil

neildm@id.doe.gov





-----Original Message-----

From: Brian Stymest [mailto:Brian_Stymest@uml.edu]

Sent: Thursday, March 14, 2002 9:56 AM

To: radsafe Listserve

Subject: soil samples





Good morning Radsfers,



If you are given soils samples (approximately 3-4 grams for each sample) and

asked to verify that there is no "significant" contamination. How far does

one go about it?



Gamma Spec--determined K-40,  Uranium Decay Series daughter as well as

Thorium Decay Series Daughters (Pb-212, Ra-226U, Bi-214,Pb-214), at levels

no greater than 2 bequerels/grams. Highest activity was for K-40, all other

were tenths of a bequerel per gram (0.XXX bqs/gram). These are all naturally

found in the ground, so I see no "significant" gamma contamination. However,

I do not have a sample from a "clean" area to use as a control/reference

background sample.



If you count on a gas flow proportional counter, you'll either get alpha &

Beta or just alpha depending on voltage settings. A count was down and

counts close to 2x background were recorded. Background in this case means,

a clean 2" planchette nothing on it, counted for 10 minutes. Knowing that

the soil contains radium/thorium daughter products I expect to see some

counts.



Liquid scintillation can't be performed directly on the soil...quenching and

self absorbtion occurs, again any alpha/beta emitter will be counted...



So what am I left with? Specific radiochemical techniques to look at H-3,

C-14??? I do not expect to see these types of radionuclides in this sample.

What activity level is clean?



Your thoughts and expertise are very much appreciated.



Brian Stymest, CHMM









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