Q. The radioactivity of a given sample of whisky due to tritium (half life 12.3 years) was found to be only 3% of that measured in a recently purchased bottle marked “7 years old”. The sample must have been prepared about
A) 220 years back
B) 300 years back
C) 400 years back
D) 70 years back
Explanation
(d) After one half life period, the activity of Tritium becomes 50%
After 2 half life period 25%
After 3 half life period 12.5%
After 4 half life period 6.25%
After 5 half life period 3.12% = 3%
It is $5 \times 12.5$ years + 7 years $i.e.$ approximately 70 years only
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.