Question

A narrow beam of 100 MeV neutrons, with a intensity 10 to the power 5

n/cm2

.s , is

normally incident on an aluminum foil. The elastic scattering cross

section of aluminum for 100 MeV neutrons is 0.95 barns. The density of

aluminum is 2.7 g/cm3

. How thick must the aluminum foil be in order to

reduce the number of unscattered neutrons emerging from the foil by

three orders of magnitude?

Answer 1

$h=\frac{E\rho}{IAn'}=1.3\cdot 10^{-8}~m.$