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1229_Physics ProblemsTechnical Physics

1229_Physics ProblemsTechnical Physics - 570 Nuclear...

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570 Nuclear Structure Q44.28 Carbon-14 is produced when carbon-12 is bombarded by cosmic rays. Both carbon-12 and carbon-14 combine with oxygen to form the atmospheric CO 2 that plants absorb in respiration. When the plant dies, the carbon-14 is no longer replenished and decays at a known rate. Since carbon-14 is a beta-emitter, one only needs to compare the activity of a living plant to the activity of the sample to determine its age, since the activity of a radioactive sample exponentially decreases in time. Q44.29 The samples would have started with more carbon-14 than we first thought. We would increase our estimates of their ages. Q44.30 There are two factors that determine the uncertainty on dating an old sample. The first is the fact that the activity level decreases exponentially in time. After a long enough period of time, the activity will approach background radiation levels, making precise dating difficult. Secondly, the
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