How much cesium- 137 will be left after 2 half-lives?

Question

The half-life of cesium-137 is 30 years. Answer the following questions assuming you start with 100 mg sample of cesium-137

A. How much Cesium-137 will be left after 2 half-lives?

B. How much Cesium- 137 will be left after 60 years?

C. How long will it take for the 100 mg of Cesium-137 to decay to 25 mg (1/4 the original amount)?


Please just any help on any question will be higly apretiatied

Answer 1

the definition of 1/2 life is that 1/2 of the material will be left after that amount of time.
100 g to start, 50 g after 1 half life.
25 g after 2 half lives.

b) 60 yrs is 2 half lives. see ans to part A)
c) 25 g will be left after 60 yrs. See answer to part A)
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Answer 2

All 3 are the same.... 2 half live = 30 years and makes 25mg of Cs 137

Answer 3

Half-life is the time it takes for half the remaining material to decay. After sixty years, you would have half of a half, or one-quarter. 60 years = two lifetimes = 25mg left. (100*0.5^2)

Answer 4

Think this through carefully.
A. 25mg
B. 25mg
C. 60years

Now please work out why!