A student uses a Geiger-Müller tube and counter to measure the count rate of a radioactive sample in a laboratory with a constant background radiation. The graph below shows how the total measured count rate varies with time.
What is the half-life of this radioactive isotope?
2.4 minutes2.4\text{ minutes}2.4 minutes
4.0 minutes4.0\text{ minutes}4.0 minutes
4.8 minutes4.8\text{ minutes}4.8 minutes
8.0 minutes8.0\text{ minutes}8.0 minutes