A radioactive substance has a half-life of 3 minutes. After 9 minutes, the count rate was observed to be 200. What was the count rate at zero time?
A
200
B
1200
C
1600
D
2400
E
4800
Verified Correct Answer: C.
Physical Principles & Numerical Solution
Let the count at zero time = Q,
then count after 3s = \(\frac{Q}{2}\)
but after 9secs., count was observed to be = 200
count after 9secs = \(\frac{Q}{8}\) = 200 ( remember here, that we are dealing with half-life)
Q = 8 x 200 = 1600
∴ count at zero time = 1600.
Source: Myschool Past Questions Archive (Record #42727)