Reply #6: Look up what a "curie" is.

[NNadir]

A curie is 3.7 X 10^10 Beq. One Bequerel is one nuclear decay.

This means that 500 billion curies of potassium-40 is 5 X 3.7 X 10^10 X 10^11 = 1.8 X 10^22 Beq or 1.8 X 10^22 decays per second. That there are this many decays is not a function of the half-life of potassium-40, which while not irrelevant to the question hardly tells the whole story, but is more a function of the vast amounts of potassium-40 on the planet.

Now if I were giving a student a quiz and I wanted him to demonstrate a modicum of understanding of radioactivity, for say, an introductory physics course, I might ask him or her to demonstrate that he or she understood the radioactive decay law (dN = -kN dt) by demonstrating that that the more radioactive material one has the more decays he or she will see.

I might phrase a quiz like this: Let us assume that the 437 nuclear commercial powerplants operating on the planet each have 1 kilogram of tritium in them. (The best students would immediately understand that is an absurdly high number given the low neutron capture cross section of deuterium and the low levels of ternary fission resulting a tritium discharge fragment. Powerplants typically have at most a few grams of tritium, if that.)

What, under these circumstances would be the total radioactivity associated with the decay of tritium (half-life 12.26 years) in Beq and in curies?

Then I might add this statement:

The ocean contains 6.6 X 10^20 grams of potassium. Of this 0.0117% is radioactive potassium-40. Given that the half-life of potassium-40 is 1.28 billion years, what is the total activity associated with the potassium-40 found in the ocean?

Then I might ask this question:

What is the ratio of the activity of tritium in 437 nuclear power plants each with one kilo of tritium in them to the activity associated with potassium-40 in the ocean?

(The answer to this last question would require, of course, an ability to answer the first two questions, which in turn would assume an ability to understand that the number of decaying nuclei is of equal importance as the half-life.)

Before a student could read my post #2 above and understand it and what it says, he or she would be probably need to be able to get 100% on this quiz. If however one did not understand radioactivity, and was not able to come to do the calculations that such a quiz would require, he or she would be might have difficulty reading my post #2 above and drawing useful conclusions about what it says. Of course, I cannot give quizzes on DU before making my posts. I am already arrogant enough without trying that particular bit of obnoxiousness.

I put my posts there for people who either have the capability of reading and understanding what they say, or, who have the time to read the links provided to teach themselves how to do the interpret my remarks. Some people have told me they find my remarks useful and others tell me frankly and honestly that they have no clue about what I am saying. A third class of persons demonstrate that they have no clue about what I am saying while insisting that they do understand what I say.

Like everyone else on DU, I am doing the best I can. I have, of course, a very distinct case on the relative risks of energy decisions and frequently I am frustrated by my poor ability to explain what I know in simpler terms than those in which I think and learn. While the third class of readers described above frustrate me even more than my own failings do, one must often deal in public discourse with clueless people who attempt to carry unjustifiable authority. (This for instance, accounts for the person occupying the White House.) Still the purpose of public discourse is not to attempt to educate those who cannot be educated or refuse to be educated, but to effect intercourse with those on such a level as to teach and to be taught, i.e. to engage in a mutual exchange that might help people to develop and disseminate a broad understanding of how we might best respond to the very real crisis we face.