A sample of a radioactive substance decayed to 96.5% of Its original amount afte
ID: 2877687 • Letter: A
Question
A sample of a radioactive substance decayed to 96.5% of Its original amount after a year. (Round your answers to two decimal places.) What is the half-life of the substance? How long would it take the sample to decay to 10% of its original amount? Dinosaur fossils are too old to be reliably dated using carbon-14, which has a half-life of about 5730 years. Suppose we had a 69 million year old dinosaur fossil. How much of the living dinosaur's^14C would be remaining today? (Round your answer to five decimal places.) Suppose the minimum detectable amount is 0.4%. What is the maximum age of a fossil that we could date using^14C? (Round your answer to the nearest Integer)Explanation / Answer
a)
[R]/[Ro] = 96.5/100 = 0.965
use:
[R]/[Ro] = e^(-k*t)
0.965 = e^(-k*1)
k = 0.0356 year-1
half life = 0.693/k
= 0.693/0.0356
= 19.5 yr
Answr: 19.5 yr
b)
[R]/[Ro] = 10/100 = 0.1
use:
[R]/[Ro] = e^(-k*t)
0.1 = e^(-0.0356*t)
0.0356*t = 2.303
t = 64.7 years
Answer: 64.7 yr
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