How much time would it take for 5.2 x 105 atoms of fermium-253 (half-life 3 days) to decay to 6.5 x 104 atoms?

Answer 1

{[log(5.2E5 / 6.5E4)] / [log(2)]} * 3 d

Answer 2

the fraction left after t days is (1/2)^(t/3)
So, solve for t in
(1/2)^(t/3) = (6.5 * 10^4)/(5.2 * 10^5) = 0.125 = (1/2)^3
so, t/3 = 3
t = 9 days, or 3 half-lives

Answer 3

5.2/.65 = 8
1/8 left
(1/2)(1/2)(1/2) =1/8
three days :)

Answer 4

I mean 3 half lives, 9 days