Carbon dating and chemistry
(b) Radioactive isotopes can be used to detect any leakage in underground pipes carrying oils, gas or water.
To check the point of leakage a small quantity of compound of radioactive isotope is introduced at the starting place and the detector is moved along the pipe.
Suppose, the ratio of uranium-238 and lead-206 is unity.
It implies that half of the uranium originally present has been converted into lead isotope.
If no radioactive isotope is detected, it means that passage of blood is hindered.
Thus, the atmospheric carbon dioxide contains a small proportion of 14C carbon dioxide (The amount of 14C in a sample can be accurately determined by counting the number of 13-particles emitted per minute by one gram of the sample.
By knowing 14C content and half-life period, the age of the sample can be determined.
The age of rock must therefore be equal to the half-life of uranium-238 i.e., 4.5 x 109 years.
Pb/U ratio of most of the rocks is 1.33 x 10-2 indicating that their age is of the order of 10s years. The abundance ratio of the two isotopes of uranium, i.e., 235U : 238U at present is 1 : 140. Assuming that in the beginning the proportion of two isotopes was equal, the above data determines the age of earth as 5 x 109 years.