The average natural background radiation received for a person in the U.S. is about 3.5 x 10-5 rem per hour. (rem is a unit useful for radiation dosage). Calculate how much radiation a person could receive in this lab if they held one of the 0.1 Ci Cs-137 sources in their closed fist for 1 hour and all of the radiation was absorbed (100 % efficiency). Assume the mass of the hand is 2 kg. The gamma radiation produced by Cs-137 is 662 keV (i.e. each decay releases a 662 keV photon). How does this compare with the average natural background radiation received in the same amount of time? Use the following conversions to obtain your answer: 1 Ci = 3.70 X 1010 decays per second 1 eV = 1.6 X 10-19 J 1 J/kg = 100 rem (for gamma rays)