Answer:
It takes 6h to the radioactive source decrease its activity from 200 to 25
Explanation:
The equation that describes the readioactive decay is:
Ln [A] = -kt + Ln [A]₀
Where [A] could be taken as activity of the source after time t, [A]₀ is initial activity and k is decay constant.
Decay constant could be written as:
k = ln2 / Half-life
k = ln 2 / 2h
k = 0.3466h⁻¹
Replacing in decay equation:
Ln [25] = -0.3466h⁻¹t + Ln [200]
-2.0794 = -0.3466h⁻¹t
6h = t
It takes 6h to the radioactive source decrease its activity from 200 to 25
