Radioactive strontium90 decays according to the formula A A

Radioactive strontium-90 decays according to the formula A = A₀(1/2)^t/28, where A is measured in milligrams and t is in years.

What is the half-life of strontium-90?                              A.________________________

What is the annual/effective decay rate?                         B.________________________

Solution

A = Ao(1/2)^(t/28)

Half life: time whenA = Ao/2

A0/2 = A0(1/2)^(t/28)

0.5 = (1/2)^(t/28)

taking natural log on both sides:

ln(0.5) = (t/28)ln(0.5)

t = 28 years

Annual effective decay rate = 0.5 = 50%