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Carbon-14 is used to determine the age of organic material. The procedure is based on the formation of 14C by neutron capture in the upper atmosphere.
147N+10n146C+1P1
14C is absorbed by living organisms during photosynthesis. The 14C content is constant in living organisms once the plant or animal dies, the uptake of carbon dioxide by it ceases and the level of 14C in the dead being, falls due to the decay which C-14 undergoes 146C147N+β
The half-life period of 14C is 5770 yr.
The decay constant (λ) can be calculated by using the following formula λ=0.693t12.
The comparison of the β activity of the dead matter with that of the carbon still in circulation
enables measurement of the period of the isolation of the material from the living cycle. The
method however, ceases to be accurate over periods longer than 30,000 yr. The proportion of 14C to
12C in living matter is 1:1012.
Which of the following option is correct?

A
In living organisms, circulation of C14 from atmosphere is high so the carbon content is constant in organism
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B
Carbon dating can be used to find out the age of earth crust and rocks
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C

Radioactive absorption due to cosmic radiation is equal to the rate of radioactive decay, hence the carbons content remains constant in living organisms

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D
Carbon dating cannot be used to determine concentration of C14 in dead things
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Solution

The correct option is A In living organisms, circulation of C14 from atmosphere is high so the carbon content is constant in organism
Living plants maintain an equilibrium between the absorption of C14 (produced due to cosmic radiation) and the rate of decay of C14 present inside the plant. This gives a constant amount C14 per gram of carbon in a living plant.

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