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Chapter: 11th 12th std standard Class Organic Inorganic Physical Chemistry Higher secondary school College Notes

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Radiocarbon Dating and Uses

This method was developed by Willard and Libby to determine the age of wood or animal fossils. This method is based onthe fact that 6C14, radioactive isotope of carbon is formed in the upper atmosphere by reaction with neutrons


RADIOCARBON DATING

This method was developed by Willard and Libby to determine the age of  wood or animal fossils. This method is based onthe fact that 6C14, radioactive isotope of carbon is formed in the upper atmosphere by reaction with neutrons (from cosmic rays).


7N14 + 0n1   --- >   6C14 + 1H1


The C14 atoms thus produced are rapidly oxidised to 14CO2 which in turn is incorporated in plants as result of photosynthesis. Animals too consume C14 by eating plants. On death, organisms cease to take in fresh carbonations. Carbon-14 begins to decay.


6C14  -- > 7N14  + -1e0


5700 years a fossil (plant or animal) will lose half the amount of carbon-14 present in its living state. Therefore by knowing either the amount of C14 or the number of b-particles emitted per minute per gram of carbon at the initial and final stages, the age of carbon material can be determined by the following equation.


 t = ( 2.303 t  / 0.693 ) log ( Amount of  C14 in fresh wood / Amount of  C14 in dead wood)


Uses

1)    Carbon dating has proved to be a great tool for correlating facts of historical importance.

2)    It is very useful in understanding the evolution of life, and rise and fall of civilizations.

 

NUCLEAR REACTIONS TAKING PLACE IN SUN (STARS)

It has been estimated that the sun is giving out energy equally in all possible directions at the rate of 3.7 1033 ergs/sec. The energy of the sun is supposed to arise from the fusion of hydrogen nuclei into helium nuclei which in going on inside it all the time.

The various fusion reactions taking place in the sun are as follows:


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