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Friday, September 4, 2015

Potassium in the Ocean, Fixing a Reporting and Rounding Error

There is some silliness going on, and I think I know the basis.    Just because you saw something somewhere, you can't strictly trust the value of it unless you know where and how it came into being.   The below is a mistake that is being repeated quoted.

"Since then there have been added at least 1,000 Bq/m^3 of man-made Potassium-40 which is not part of natural potassium" 

has been quoted several times at ENE, with the implication that man has added 1000 Bq/M3 to the ocean.    

PT had stated 11,000Bq/M3 from a 1971 source.    And then later I calculated 11,800 or round to 12,000
So out of that became  the "1000 bq/m3 of man-made Potassium-40" added

Let's trace the original information

Going to the source document (which is embedded in this post at the far bottom)

From the source document, they use an unusual convention dpm/minute.    K40 decays 90% as a beta, 10% as a gamma.   And Geiger counters are not of perfect efficiency, i.e. they don't catch every disintegration.   Wait for the punchline, but review this first.

NukePro Calcs below and shown originally on this post

By knowing the "Specific Activity" of K-40 it is then simple to calculate the Bq/Liter, or Bq/M3

Specific Activity 265400 Bq/g

Which is used in my calculation, its one of the blue shaded values above.

So rather than using the scientific specific activity, they used a field measured dpm, and that is the error.     So if their Geiger was 93% efficient, then the 670 dpm, you would add 7% to bring the low efficiency measurement up to the real Bq/min or 717 and then divide that by 60 seconds to arrive at 11.94 Bq/L, and then convert that to M3

11, 940 Bq/M3 Now that is More Like Reality

So all this misunderstanding and "creation of human generated K-40" was simply due to a non perfect Geiger Counter, and an author who choose to round down to 11,000 even. 


Source Document

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