A narrow beam of thermal neutrons passes through a plate of iron whose absorption and scattering effective cross-sections are equal to \(\sigma_{a}=2.5 \mathrm{~b}\) and \(\sigma_{s}=11\) b respectively. Find the fraction of neutrons quitting the beam due to scattering if the thickness of the plate is \(d=0.50 \mathrm{~cm}\)