Aradioactive sample of a pure element produces 30240 decays per minute at one point in an experiment and 101.95 minutes later, produces 945 decays per minute. what is the half-life? (ii) what is the decay constant? (iii) what is the mean lifetime of the element? (b) what fraction of a sample of sodium-22 is left after 6.505 yr. (the half-life of sodium-22 is 2.602 yr.) (c) what period of time is required for a sample of radioactive carbon-14 to lose 66.667% of its activity? (the half-life of carbon-14 is 5730 yr)