A 75 kg laboratory technician working with the radioactive isotope 137Cs receives an accidental 100 mrem exposure. 137Cs emits 0.66 MeV γ-ray photons.

a) How many γ- ray photons are absorbed in the technician’s body?

b) How many rad of alpha radiation with an RBE of 10 will cause the same biological damage as the gamma ray above?

For a), I got 7.1 x 10^11 photons, am I correct?
I don't know how to solve for b)!!

Thanks