The half-life of strontium 90 is 28 years.
(a) Obtain an exponential decay model for strontium 90 in the form
Q(t) = Q0e−kt.

Question

The half-life of strontium 90 is 28 years.
(a) Obtain an exponential decay model for strontium 90 in the form 
Q(t) = Q0e−kt.

anonymous · Answer

Use your model to predict, to the nearest year, the time it takes two-thirds of a sample of strontium 90 to decay.

campbell_st · Answer

well you need to find the value of k

so let the initial quantity be 1 so the quantity after 28 years is 1/2

so substituting into the formula 

$$0.5 = 1 \times e^{-k \times 28}$$

take the log of both sides

$$\log_{e}(0.5) = -28k$$

you should be able to evalaute k...from here..

anonymous · Answer

k=.01075

campbell_st · Answer

ummm not quite

$$k = \frac{\log_{e}(0.5)}{-28} = $$

i got 0.024755...