A parallel beam of 500 keV photons is normally incident on a sheet of lead 8 mm thick. The rate of energy transmission is 4 x 10^4 MeV/s.

A parallel beam of 500 keV photons is normally incident on a sheet of lead 8 mm thick. The rate of energy transmission is 4 x 10^4 MeV/s.

a. what fraction of the incident photon energy is absorbed in the sheet?

b. how many photons per second are incident on the sheet?

c. What fraction of the transmitted energy is due to uncollided photons?

I know the answer

A. 0.598

B. 1.99 x 195 s^-1

C. 0.580

Please tell me why!