Question

If you have 100.g of a radioactive isotope with a half-life of 10. years, how much of the isotopewill you have left after 20. years?

Answer 1

Use the radioactive decay formula using t_0 as the half life:

`A=A_0\cdot2^(-t/t_0)`

Substitute the initial amount of radioactive element A_0=100g, the half life t_0=10y and the time period t=20y to find the remaining amount after 20 years:

`\begin{gathered} A=100g*2^(-20y/10y) \\ =100g*2^(-2) \\ =100g*(1)/(4) \\ =25g \end{gathered}`

Therefore, after 20 years, there are 25 grams left.