^14 C is produced in the upper atmosphere by cosmic rays. Living organisms uptak

Question

^14 C is produced in the upper atmosphere by cosmic rays. Living organisms uptake^14C. Assume we isolate the same quantity of^14C from a 1000 year old fossil and from a recently harvested tomato. We monitor the decay of these quantities. Which of the following is true? Explain. The carbon isolated from the tomato plant will have more decays per second that the carbon isolated from the fossil. The carbon isolated from the fossil will have more decays per second that the carbon isolated from the tomato plant. The two samples will have approximately the same number of decays per second. It is impossible to compare the decay rates, since nuclear decay is a random process. If the mass of a radioactive sample is doubled, the decay constant. Explain. doubles, remains the same. decreases by a factor of 1/2. decreases by a factor of ln(2). A 5 g charcoal sample from an ancient pit has a carbon 14 activity of 63 disintegrations per minute. A living tree has a carbon 14 activity of 15.3 disintegrations per minute per gram. The half life of carbon 14 is 5730years. How old is the sample? Explain. tilde 970 years tilde 240 years tilde 1600 years tilde 2000 years tilde 3400 years

Explanation / Answer

(7) Option (c) is the correct answer.

Both will decay with the same rate.

(8) Option (b) is the correct answer.

The decay - constant is not affected by doubling the sample. For a certain isotope it is a constant.

(9) Option (c) is the correct answer.

Here, the sample activity is 63/5.0 = 12.6 events/min-g
So, no. of halflives = ln(12.6/15.3)/ln(0.5) =-0.1941 / -0.6931 = 0.28

So, t = thalf*0.28 = 5730*0.28 = 1604 years.

This is nearest to option (c)

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