Question Detail
Question
The count rate from a radioactive isotope is recorded every hour. The count rate is corrected for background radiation. The table shows the readings. What estimate of the half-life of the isotope can be obtained from the readings in the table? (Table: time/hours: 0,1,2,3,4,5; count rate: 800,620,480,370,290,220)
Correct Answer
Option A is the correct answer.
Detailed Explanation
The half-life is the time it takes for the count rate to drop to half its initial value. The initial count rate is 800 counts/s. Half of this is 400 counts/s. Looking at the table, the count rate drops from 620 at t=1 hour to 480 at t=2 hours. The rate reaches 400 between 1 and 2 hours.
Hint
Find the time it takes for the count rate to halve from its initial value. Look for where the value drops to half of the original.