Quantum Physics

972 Chapter 29 Nuclear PhysicsACTIVITIES1. This experiment will take a little longer to do thanmost that we have suggested, but the time spent isworthwhile to help you understand the concept ofhalf-life. Obtain a box of sugar cubes and with apencil make a mark on one side of each of about200 cubes. Each of these cubes will represent thenucleus of a radioactive substance. Thus, at t 0,you have 200 undecayed nuclei. Now, put the 200marked cubes in a box and roll them out on a table,just as you would roll dice. Next, count and removeany cubes that have landed marked-side up. Thesecubes represent nuclei that emitted radiation duringthe roll. They are no longer radioactive and thusdo not participate in the rest of the action. Recordthe number of undecayed cubes remaining as thenumber of undecayed nuclei at t 1 roll.Continue rolling, counting, and removing untilyou have completed 12 to 15 rolls. By then, youshould have only a few cubes remaining. Plot agraph of undecayed cubes versus the roll numberand from this determine the “half-roll” of the cubes.2. Use a nail to punch a hole in the bottom of a largetin can. Hold the can beneath a faucet and adjustthe water flow from the faucet to a fine constantstream. Although water flows from the hole at thebottom, you will note that the level of the water inthe can rises. As it does so, however, the flow of waterleaving the can increases due to increased waterpressure caused by the greater depth of water. Unlessthe flow of water is too great, an equilibriumpoint will be reached at which the amount of waterflowing out of the can each second exactly equalsthe amount flowing in each second. When this happens,the level of water in the can is constant. Asnoted in the text, carbon-14 is continually beingproduced in the atmosphere and is also continuallydisappearing as it decays into nitrogen. What is theanalogy between water entering the can, remainingin the can, and flowing out of the can and the behaviorof carbon-14 in the atmosphere?