Problem 6.9

A narrow beam of alpha particles with kinetic energy $1.0 \mathrm{MeV}$ falls normally on a platinum foil 1.0 $\mu$ m thick. The scattered particles are observed at an angle of $60^{\circ}$ to the incident beam direction by means of a counter with a circular inlet area $1.0 \mathrm{~cm}^{2}$ located at the distance $10 \mathrm{~cm}$ from the scattering section of the foil. What fraction of ecottoi reaches the counter inlet?