The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 97.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
u = Uo e^-kt
u/Uo = .5 = e^-k(2.52*10^5)
-ln .5 = -2.53*10^5 k
k =2.74*10^-6
.977 = e^-kt
-ln .977 = -2.74*10^-6 t
t = 8943 years
or 9,000 years