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 thicknes of lead, which will reduce the intensity to I/2 will be:

Options

A. 6 mm
B. 9 mm
C. 18 mm
D. 12 mm

Answer

D

Explanation

Intensity of gamma radiation when it passes through `x` is `I = I_(0) e^(-mu x)`
`rArr (I_(0))/(8) = I_(0) e^(-mu(36))` ....(i) and `(I_(0))/(2) = I_(0) e^(-mu (x))` ......(ii)
`(1)/(8) = e^(-36mu)` and `(1)/(2) = e^(-mu x) rArr e^(3 mu x) = e^(-36 mu) rArr x = 12 mm`