The intensity of gamma radiation from a given source is I. On passing through 36 mm of lead, it is reduced to I/8. The thickness of lead which will reduce the intensity to I/2 will be (a) 9 mm (b) 6 mm (c) 12 mm (d) 18 mm

Answer: (c). Intensity halves for every half-value thickness x1/2. I/8 = I/2³, so 36 mm = 3x1/2. x1/2 = 12 mm So the answer is (c) 12 mm.

The intensity of gamma radiation from a given source is I. On passing… | JEE Main 2005 (AIEEE)

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Radioactive Decays: Alpha, Beta, Gamma

The intensity of gamma radiation from a given source is $\text{I}$ . On passing through $36\text{ mm}$ of lead, it is reduced to $\frac{\text{I}}{8}.$ The thickness of lead which will reduce the intensity to $\frac{\text{I}}{2}$ will be

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Answer: (c)

Intensity halves for every half-value thickness $x_{1/2}$ .
$\dfrac{I}{8} = \dfrac{I}{2^3}$ , so $36\text{ mm} = 3x_{1/2}$ .
$x_{1/2} = 12\text{ mm}$
So the answer is (c) $12\text{ mm}$ .

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