Cobalt-60 was a mean life of 5.22 yrs. It decays by beta emmision and then by gamma rays of about 1 MeV. A person weighing 80 kg with a projected area od .8 m^2 can stand a safe distance of 40 m per year away from source. A safe dose rate is 50 mSv/yr. Calculate what fraction of gamma rays passing this person must be absorbed for this safe distance to be true.