Answer:
If you have a 120 gram sample of a radioactive element, how many grams of that element will be left after 3 half-lives have passed?
Solution
Given: mass of radioactive sample of an element, number of half-lives
Asked to Solve For: mass of radioactive element after so many half-lives
Solve:
All radioactive samples lose half of their mass after each half-life. Thus, one solution is to calculate the mass after each half-life. (This method only works if you are asked to solve for a whole number of half-lives). Let the passing of time equal to one half-life be represented by and arrow, →. Then the solution is:
120 g → 60 g → 30 g → 15 g
If you want to solve for any number of half-lives, including fractional half-lives, then you use the equation: amount remaining = (12)n(amountatstart) , where n= number of half-lives. Then the solution is:
amount remaining = (12)3(120g)=15g
Explanation:
