1. The photon fluence rate is 107 photons mm-2 sec-1 for a beam of γ rays. One fourth of the photons have energies of 100 keV, one half have energies of 80 keV and the remaining quarter have energies of 20 keV. What is the energy flux density (energy fluence rate) of the beam? If the photon flux density (fluence rate) is constant, what is the energy fluence over an interval of 40 seconds?