Question

Radon 86222Rn is a radioactive gas with a half-life of 3.82 d. If there are initially 400 decays/s in a sample, how many radon nuclei are left after 2 d ?

Please help, I don't understand how to do this.

Answer 1

The half-life is 3.82 days
That means that every time 3.82 days have passed, 1/2 of it is gone. So, starting with 400 nuclei, after 2 days there will be

400(1/2)^(2/3.82) = 278