How Long Is the Half-Life of an Isotope if a Sample of the Isotope that Registers 60000 cpm on the Geiger Counter Decays to 15000 cpm After 150 Minutes?

Answer 1

To determine the half-life of the isotope, we can use the decay formula, which states that the activity decreases by half with each half-life. Starting with 60,000 cpm and decaying to 15,000 cpm indicates a reduction by a factor of four, meaning two half-lives have passed (since (60,000 \to 30,000) to (15,000)). Given that this decay occurs over 150 minutes, the half-life of the isotope is 75 minutes.