41.40. A radioactive material produces 1370 decays per minute at one time, and 3.8 h later produces 310 decays per minute. What is its half-life? 41.41. What fraction of a sample of 32 bo Ge, whose half-life is about 9 months, will remain after 2.2 years? 41.44. A sample of 60 Co and a sample of 151 "I both have NO atoms at t=0. How long will it take until both have the 27 53 same activity? (Use Appendix F in the textbook for half-life data.)