# Radioactive Decay

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• October 12th 2009, 12:31 PM
Royster123
Radioactive Decay
If Forty percent of a radioactive substance decays in five years. By what percent does the substance decay each year?
• October 12th 2009, 12:51 PM
e^(i*pi)
Quote:

Originally Posted by Royster123
If Forty percent of a radioactive substance decays in five years. By what percent does the substance decay each year?

Exponential Decay: $N(t) = N_0e^{-\lambda t}$

$0.6 = 1e^{-40\lambda}$

$\lambda = -\frac{1}{40}ln(0.6)$

$
N(t) = 1e^{-\left(-\frac{1}{40}ln(0.6)\right) \times 1)}$