The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life of 30 minutes decreases to 5 second⁻¹ after 2 hours. The initial count rate was (a) 80 second⁻¹ (b) 625 second⁻¹ (c) 20 second⁻¹ (d) 25 second⁻¹

Answer: (a). Count rate ∝ activity, which halves every half-life. 2 h = 120 min, so n = 120/30 = 4. Initial rate = 5 × 2⁴ = 80 s⁻¹. So the answer is (a) 80 second⁻¹.

The count rate of a Geiger Muller counter for the radiation of a… | NEET 1995 (AIPMT)

Q122NEET 1995 · AIPMTEasy

Law of Radioactive Decay

The count rate of a Geiger Muller counter for the radiation of a radioactive material of half-life of 30 minutes decreases to 5 $\text{second}^{-1}$ after 2 hours. The initial count rate was

Show answer and solution

Answer: (a)

Count rate $\propto$ activity, which halves every half-life.
$2\text{ h} = 120\text{ min}$ , so $n = \frac{120}{30} = 4$ .
Initial rate $= 5 \times 2^4 = 80\ \text{s}^{-1}$ .
So the answer is (a) 80 $\text{second}^{-1}$ .

Report a mistake

Law of Radioactive Decay question from NEET 1995 (AIPMT)

More questions on Law of Radioactive Decay