Question 8: NCERT Solutions for 12th Class Physics: Chapter 13-Nuclei
The normal activity of living carbon-containing matter is found to be about 15 decays per minute for every gram of carbon. This activity arises from the small proportion of radioactive
present with the stable carbon isotope
. When the organism is dead, its interaction with the atmosphere (which maintains the above equilibrium activity) ceases and its activity begins to drop. From the known half-life (5730 years) of
, and the measured activity, the age of the specimen can be approximately estimated. This is the principle of
dating used in archaeology. Suppose a specimen from Mohenjodaro gives an activity of 9 decays per minute per gram of carbon. Estimate the approximate age of the Indus-Valley civilization.
Solution:
In order to estimate age, let us first find the activity ratio in form of time ‘t’. Given normal activity, R0 = 15 decays min-1 Present activity, R = 9 decays min-1, Tin = 5730 years Since activity is proportional to the number of radioactive atoms, therefore,
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NCERT Solutions for 12th Class Physics: Chapter 13-Nuclei