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).
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...
Both figures are right, but they describe different situations.
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.
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.
You’re joking...if so, good one.
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?
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.
If you could nail something down, it could be a game changer for potassium-argon dating ?
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