The intensity of gamma radiation from a given source is I. On passing through 36mm of lead, it is reduced to 1/8.The thickness of lead, which will reduce the intensity to 1/2 will be:
A
6mm
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B
9mm
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C
18mm
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D
12mm
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Solution
The correct option is D12mm
I=I0e−μd where "d" is thickness of lead
II0=e−μdeμd=I0Iμd=ln(I0I)
when d=36,I=I0/8μ36=ln(I0I0/8)=ln(8)−−(1) for I=I0/2 ; lead thickness bed μd=ln(2)−−(2) (1)/(2) ⇒36d=3⇒d=12mm