Question

The isotype caesium -137, which has a half life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotype in a sample of caesium to decay to one-sixteenth of its original amount?

first half life 1/2
second 1/4
third 1/8
fourth 1/16

so how long is four half-lives?

120 years

30=1/2
60=1/4
90=1/8
120=1/16

Answer 1

try the equation No= 1/2^n