Cesium137 a beta emitter has a halflife of 30 y How many mil

Cesium-137, a beta emitter, has a half-life of 30 y. How many milligrams of a 16 mg sample of cesium-137 would remain after 90 y? 0.13 mg 0.25 mg 0.5 mg 1.0 mg 2.0 mg 4.0 mg

Solution

The correct answer is : 2mg.

Explanation:

We will start taking 16 mg

Half life is 30 y.So, after 30 y Cs left will be 16/2 = 8 mg
Again, after next 30 y(means 60 y),Cs left will be 8/2 = 4 mg
Again ,after next 30 y;(means 90 y), Cs left will be 4/2 = 2mg ( ans)