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.
14C is absorbed by living organisms during photosynthesis. The 14C content is constant in living organism. 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 14C undergoes.
The half-life period of 14C is 5770yr. The decay constant (λ) can be calculated by using the following formula
λ = 0.693/t1/2.
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 options is correct?
(a) In living organisms, circulation of 14C from atmosphere is high, so the carbon content is constant in organism.
(b) Carbon dating can be used to find out the age of earth crust and rocks.
(c) Radioactive absorption due to cosmic radiation is equal to the rate of radioactive decay. hence the Carbon content remains constant in living organisms
(d) Carbon dating cannot be used to determine concentration of 14C in dead beings.
