Isotopes as tracer in carbon dating
Each disintegration step has a definite half-life and hence a definite decay constant.
Thus, by determining the amounts of parent radioactive element and the isotope of lead in a sample of rock, the age of rock can be calculated.
This technique is gaining importance in analytical chemistry these days.
It can help in the detection of even one part of the element per billion parts of the sample.
Absence of salt penetration indicates absence of cracks.Sulphuric acid is then added to the aqueous solution to precipitate lead as lead sulphate.γ-rays emitted by the radio isotopes (Co) can be used in the treatment of cancer.The basis of such a treatment is, that the radiation tend to destroy cancerous cells more easily than the normal cells.In this technique, the sample containing very small amount of the stable isotope of the element to be investigated is bombarded with neutrons and the element of interest is converted (i.e., activated) into its radioactive isotope.
The radioactivity of this radioisotope is measured.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.Suppose, the ratio of uranium-238 and lead-206 is unity.