The Intensity of Gamma Rays Passing Through a Material as a Function

Multiple Choice

The intensity of gamma rays passing through a material as a function of thickness,x is given by where n is the number of atoms per cm³ and $\sigma$ is the absorption cross section.It is observed that the intensity of gamma rays of a particular energy is reduced by half when they passed through 1 cm of lead.What is the thickness of lead needed to reduce the intensity to a quarter?

A) 1.0 cm
B) 1.5 cm
C) 2.0 cm
D) 3.0 cm
E) 4.0 cm