37. A sample of 4 g of cobalt isotope is produced. If the half-life of is 30 years, what will be the mass of the cobalt remaining after 90 years? Please show all work

38. Name the three different types of radiation and describe how they are different in their penetrating abilities. Please use 3 content related sentences.

39. The transmutation of a radioactive uranium isotope, , into a radon isotope, , involves a series of three nuclear reactions. At the end of the first reaction, a thorium isotope, , is formed and at the end of the second reaction, a radium isotope, , is formed. In both the reactions, an alpha particle is emitted. Write the balanced equations for the three successive nuclear reactions. Please show all work.

40. Determine the amount of time for polonium-210 to decay to one fourth its original quantity. The half-life of polonium-210 is 138 days. Please show all work.