Question
Question: A count rate meter shows a count of 240 per minute from a given radioactive source. One hour later, ...
A count rate meter shows a count of 240 per minute from a given radioactive source. One hour later, the meter shows a count rate of 30 per minute. The half-life of the source is :
A
20 min
B
40 min
C
80 min
D
120 min
Answer
20 min
Explanation
Solution
240 –® 120 –® 60 –® 30
3 half lives = 60 minutes
1 half life = 20 minutes