An isotope of cesium-137 has a half-life of 30 years. Cesium-137 disintegrates over a period of 90 years. How much of cesium-137 would remain, provided the initial amount was 1g?
- First, let us find out how many half-life 90 years are going to be. For that we will divide 90 with the half-life provide in the question.
- T =90 years/30 years ,that will give us 3T ,that means 90 years will have 3 half-life.
- As mentioned in the problem ,the initial amount of cesium is 1g
- Now let’s find out how many grams of cesium will be left after 3 half-life
- Amount left after first half life (1T) = 1/2 = 0.5 g
- Amount left after second half life (2T) = 0.5/2 = 0.25 g
- Amount left after third half life (3T) = 0.25/2 = 0.125 g
The next step, what if they ask the percentage of the cesium left?
- After 1T=100/2 =50%
- After 2T=50/2= 25%
- After 3T =25/2=12.5%