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Need help with some radiological facts [vanity, help]
01/06/2017 | self

Posted on 01/06/2017 8:51:18 PM PST by logi_cal869

Hi, all. Long story short, I need some help from any FR science geeks or professionals out there. My resources are limited.

Simply, there are two very diverse figures provided for the radioactivity of Potassium-40.

One is the figure 0.0000071 Ci/g, best-sourced from this Fact Sheet from Argonne National Laboratory. https://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf

Others are the approximately- corresponding figures of 818 pCi/g, 30 kBq/kg (800 pCi/g, or 810 pCi/g, depending on which converter you use) and 8.54E-10, one of which is cited in the National Research Council book, Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials...the basis of the EPA Guidelines for Exposure to Naturally Occurring Radioactive Materials.

If anyone can impart clarification, I would greatly-appreciate it. I realize it's a small thing, but accuracy in something I'm working on is important to me. That and I'm having trouble with little ol' me finding fault in an ANL publication (the conclusion which appears more possible than the National Research Council collectively getting it wrong on the basis for national policy regarding natural radionuclides in the environment).


TOPICS: Education; Weird Stuff
KEYWORDS: radionuclides
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To: Mount Athos

Thanks for that, but the Plexus page was my original reference. When I discovered the citation of 818 pCi/g elsewhere doing other research, it quickly became a conundrum. My frustration was at its height when I posted here.

With no reference, the only 2 official sources I could find are ANL and NRC (National Research Council), both having published very different numbers. Hence my request also for source(s) I may not be privy to or unsuccessfully-sourced despite all my time on this very stupid problem...that just so happens to have a corresponding impact that’s not so stupid...


21 posted on 01/07/2017 9:18:41 AM PST by logi_cal869 (-cynicus-)
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To: logi_cal869
If you have a chunk of potassium from a natural source it will be radioactive. Why? Because a small fraction of that natural potassium is potassium-40. The discrepancy between radiation per gram is like measuring the car exhaust from a parking lot of 8000 cars of which only one is running. Do you report the exhaust per car (the 0.000000000818 figure for potassium) or the exhaust per running car (the 0.0000017 figure from ANL for potassium-40).

Both figures are right, but they describe different situations.

22 posted on 01/07/2017 9:35:33 AM PST by KarlInOhio (a government contract becomes virtually a substitute for intellectual curiosity - Pres. Eisenhower)
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To: logi_cal869
Others are the approximately- corresponding figures of 818 pCi/g, 30 kBq/kg (800 pCi/g, or 810 pCi/g, depending on which converter you use) and 8.54E-10, one of which is cited in the National Research Council book, Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials...the basis of the EPA Guidelines for Exposure to Naturally Occurring Radioactive Materials.

Me and my buds were talking about that very subject last night in the bar after bowling.........I wish I could remember what they said since they may have had the answer you're looking for.

23 posted on 01/07/2017 9:40:36 AM PST by Hot Tabasco
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To: smokingfrog

If I’m right, it’s no laughing matter. But if I were in your shoes I’d be joking as well.
I’ll follow up later on this whether or not I receive an answer here.


24 posted on 01/07/2017 10:14:20 AM PST by logi_cal869 (-cynicus-)
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To: Hot Tabasco

You’re joking...if so, good one.


25 posted on 01/07/2017 10:16:09 AM PST by logi_cal869 (-cynicus-)
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To: KarlInOhio
You are absolutely correct, except for one little problem: Sources are citing 0.0000071 Ci/g for Potassium 40, not for Natural Potassium in quantity. Aside from the fact that the ANL fact sheet is pretty clear:

The specific activity of K-40 is 0.0000071 Ci/g.

The Plexus site in particular correctly cites the 8.54E-10 figure "per gram of natural K", but also cites it as shown below (stated units = curies/gram):

http://www.iem-inc.com/information/tools/specific-activities

Again, either the ANL booklet has a typo or there's a more fundamental problem (as published, it is either right or wrong...I lean toward a typo); a better source for the radioactivity of Potassium 40 exists...somewhere. Shouldn't it?

26 posted on 01/07/2017 12:02:31 PM PST by logi_cal869 (-cynicus-)
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To: logi_cal869
The Plexus site in particular correctly cites the 8.54E-10 figure "per gram of natural K",

OK, no argument there.

but also cites it as shown below (stated units = curies/gram):

http://www.iem-inc.com/information/tools/specific-activities

Yes. That gives the radioactivity of K-40 as 7.04E-6 Ci/g which is slightly off the ANL value of 7.1E-6 Ci/g, and the radioactivity of natural K of 8.54E-10 Ci/g (854 pCi/g). The second line merely indicates that K-40 is the only radioactive isotope of potassium found in natural potassium, unlike most of the other elements in the table which have multiple radioactive isotopes. There are many other radioactive isotopes of potassium, but they all have a half-life of less than a day so won't be found in meaningful quantities in natural potassium.

Again, either the ANL booklet has a typo or there's a more fundamental problem (as published, it is either right or wrong...I lean toward a typo); a better source for the radioactivity of Potassium 40 exists...somewhere. Shouldn't it?

I guess I'm just not seeing your problem. K-40's radiation is the same in all the sources allowing for slight roundoff or measurement accuracy errors. Call it 0.0000071 Ci/g, 7.04E-6 Ci/g or 7.1 µCi/g you have the same result. Dilute that with 99.988% non-radioactive isotopes of potassium and you get 8.54E-10 Ci/g ( or 854 pCi/g ) of the natural mixture. All the sources on the net have about the same value, even backing out the value from the farcical "banana equivalent dose" which largely comes from the potassium content of the standard banana.

27 posted on 01/07/2017 1:09:58 PM PST by KarlInOhio (a government contract becomes virtually a substitute for intellectual curiosity - Pres. Eisenhower)
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To: logi_cal869

If you could nail something down, it could be a game changer for potassium-argon dating ?


28 posted on 01/07/2017 5:21:29 PM PST by smokingfrog ( sleep with one eye open (<o> ---)
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