3. (a) In a medium consisting of 10" atoms of fissile material, a total neutron flux, , is sustained at 5 x 10" neutrons.cm'.s". If the reaction rate is 1.5x10" reactions.cm'.s"', calculate the macroscopic and microscopic cross sections of the medium. (b) In a typical thermal fission of "U as shown below, calculate the instantaneous fission energy. on + 235 92 U - 236 92 U140 $5 Cs+ Rb + 3(on)