Posted by Angie on Wednesday, April 15, 2009 at 11:47pm.
The number of radioactive atoms has decayed to 8/32 = 1/4 of the original value. That takes two half lives.
Why two half-lives?
Angie, you can also work the problem as I showed you on the 30 mCi problem you had earlier.
k = 0.693/1000 years = 6.93 x 10^-4
ln(No/N) = kt
[No is the number of atoms we started with; N = number of atoms today]
ln(32/8) = 6.93 x 10^-4*t
ln 4 = 6.93 x 10^-4*t
1.386/6.93 x 10^-4 = t = 2,000 years.
ok thanks
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