What is the decay rate of iodine 125 with a half life of 60.1 days?

Question

The book asks us to use the equation

E= ∫₀^a P₀ e^-kt dt. (integral from 0 to a)

Where k is the decay constant for the radioactive material, a is the number of years since the implant, and P₀ is the initial rate at which energy is transmitted.

Suppose that the treatment uses iodine-125, which has a half life of 60.1 days.

Find the decay rate, k, of iodine-125.

The back of the book says it is 4.20963.

Answer 1

A = a₀e^kt

0.5 = e^kt

ln 0.5 = 60.1k

Can you solve for k and answer?