Question

The half-life of phosphorus-32 is 14.26 days. The decay constant is k=4.86×10−2/days. If you accidentally spill phosphorus-32 onto your shoe, how long would it take before 99.9% of the radioactive material has decayed so that you can safely wear the shoes again?

Answer 1

.001=e^-.692t/th

-.693*t/14.26 = ln .001
t= 142 days? check that.

Answer 2

ln(No/N) = kt
Substitute for No = 100
N = 100-99.9
Solve for t in days.

Answer 3

Yeah, thanks.