Question

The half-life of radioactive strontium-90 is approximately 28 years. In 1960, radioactive strontium-90 was released into the atmosphere during testing of nuclear weapons, and was absorbed into people's bones. How many years does it take until only 15 percent of the original amount absorbed remains?

Answer 1

Answer: It will take about 77 years (76.8 years).

Step-by-step explanation: Time is given by the equation: N=No.e^kt. You know that the concentration has to be 15% from the original so N=15 and No=100. To determine k, you have to look at the half-life. k=ln(0.5)/half-life time. For 28 years, k=-0.0247. Replacing it back into the N=No.e^kt equation, the answer will be 76.8 years.