Table of Nuclides

Frequently Asked Questions

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2.1: Decay Data
Decay Constant

I have read of a "decay constant" in regard to radioactive decay.  What is the "decay constant" of Potassium-40?

The decay of radioactivity by time is governed by
  A(t)=A(0) exp(-lambda t)
where lambda = decay constant.
The half life it the time at which the radioactivity become half.
  exp(-lambda T) = 0.5
 T = ln(2) / lambda

K-40 half life is 1.277x10^9 year.
So lambda = 0.5428x10^-9 year^-1

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