The observed decay rate from a gram of living plant (sample is zero years old) is 15.3 disintegrations per minute. The observed rate from an older specimen will be less, because some of the carbon-14 will have decayed.
The amount of C-14 remaining after 15300 years will be 1/2 raised to the power of 2.67 times the amount in a fresh sample. (1/2) ^ 2.67 = 15.3 * 0.157 = 2.40 disintegrations per minute.
Jan 15th, 2015
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