The isotope Cesium-137, which has a half-life of 30 years, is a product of nuclear power plants. How long will it take for this isotope to decay to about one-sixteenth its original amount?

The answer to your question is 120 years

Explanation:

Data

half-life = 30 years

decay of 1/16

Process

1. Do a chart to solve this problem

Every 30 years the amount of Cesium is half the previous amount.

                       Amount of Cesium-137          Time (years)

                                       x                                  0

                                       x/2                               30

                                       x/2/2 = x/4                   30

                                       x/4/2 = x/8                   30

                                       x/8/2 = x/16                  30

Total time = 30 + 30 + 30 + 30 or 4 x 30 = 120 years