Solve the following questions:
Question I: A radioactive sample produces 3840 decays per minute at one point in an experiment and 308.09 days later produces 240 decays per minute.
Part a: What is the half time?
Part b: What is the decay constant?
Part c: What is the mean lifetime of the material?
Question II: What fraction of a sample of cobalt-60 is left after 36.8956 yr. ( the half-life of cobalt-60 is 5.2708 yr.)
Question III: What period of time is required for a sample of radioactive oxyden-15 to lose 99.5% of its activity? (The half-life of uranium is 122.24 yr).
Give the detailed explanation of above question.