A substance has half of 3 min. After 6 min, the count rate was observed to be 400. What was its count rate at zero time?
A
1600
B
1200
C
200
D
2400
Verified Correct Answer: A.
Physical Principles & Numerical Solution
Let the count rate at zero time be N
N \(\frac{3 min}{\to}\) \(\frac{N}{2}\) \(\frac{3 min}{\to}\) \(\frac{N}{4}\)
\(\frac{N}{4}\)
= 400
N = \(\frac{400}{N/4}\) x N
= 1600
Source: Official Exam / Past Question Archive