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Q & A: Half life of radioactive substances

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Most recent answer: 05/04/2009
what is half life???
- Fatima (age 16)
All radioactive nuclei decay with an exponential rate.  The formula for the number of nuclei remaining is N(t) = N0 e-t/tau  where N0 is the number at t = 0 and tau is the 'lifetime' of the nucleus.  If you set N(t1/2) / N= 1/2 and solve for t1/2 you find   t1/2 = ln(2)  ~ 0.693 tau.


We can give a simple example. Tritium, the radioactive form of hydrogen, has a half-life of 12.3 years. If you have a tritium supply, in 12.3 years half of it will be gone. After another 12.3 years half of the remainder will be gone, so you'll only be left with a quarter of the starting amount. etc. Mike W.

(published on 05/04/2009)

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