I think I understand what you’re trying to demonstrate. Yes, the math is academic.
However, if Potassium-40 is 0.012% of ‘naturally-occurring potassium’ - and only Potassium-40 is radioactive - then the 0.0000071 figure is nonsensical, suggesting that ALL natural potassium is radioactive.
The conclusion I came to is that an intern building the fact sheet made a boneheaded math error and represented the total possible radioactivity for 100% of naturally-occurring potassium, rather than the 0.012% figure, which in reality only represents the elemental breakdown, not the percentage of radioactivity.
Either I found an error, or the facts are escaping me still and I’m stuck in a boneheaded brainfart.
This is why I asked for help: I need other source(s) for data for which I’ve been unsuccessful or validation of my conclusion, that the 818 pCi/g figure is correct and that ANL, frankly, goofed.
In fact, the National Research Council source predates the ANL fact sheet by 6 years, published 1999....
...which just happens to state it matter-of-factly as such:
Potassium-40 is present at 0.0117% by mass in natural potassium, thereby imparting a specific activity of about 30 kBq/kb (800 pCi/g) of potassium.
I can accept a discrepancy of 0.0117% vs. 0.012%, but not 0.0000017 vs. 0.000000000818...
Both figures are right, but they describe different situations.