Posted by Bree on Tuesday, December 21, 2010 at 6:59pm.
If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value?

Science  Damon, Tuesday, December 21, 2010 at 9:01pm
1/2 = e^5k
ln .5 = 5 k
k = .1386
so
x = Xo e^.1386 t
.001 = e^.1386 t
6.91 = .1386 t
t = 49.8 days
check
about 10 five day periods
.5^10 = .000976
close enough to .001