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January 31, 2015

January 31, 2015

Posted by **Angie** on Wednesday, April 15, 2009 at 11:47pm.

a. 1000 years

b. 2000 years

c. 3000 years

d. 4000 years

- Science -
**drwls**, Thursday, April 16, 2009 at 1:00amThe number of radioactive atoms has decayed to 8/32 = 1/4 of the original value. That takes two half lives.

- Science -
**Angie**, Thursday, April 16, 2009 at 1:27pmWhy two half-lives?

- Science -
**DrBob222**, Thursday, April 16, 2009 at 3:15pmAngie, 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.

- Science -
**Angie**, Thursday, April 16, 2009 at 3:41pmok thanks

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