Physics · May / June 2026 · Paper 11 · Question 35

A student uses a radiation detector to measure the count from a radioactive source. Without any source present, the count he obtains in 2.0 min is $C_1$. With the counter next to the source, the count he obtains in 2.0 min is $C_2$. What is the count rate from the source alone, measured in counts / min?

1. A$C_2 - C_1$
2. B$C_2 + C_1$
3. C$\frac{C_2 - C_1}{2.0}$
4. D$\frac{C_2 + C_1}{2.0}$

As printed in the paper