5. No licensee may irradiate food save with—E+W
(a)gamma rays from the radionuclide 60Co;
(b)gamma rays from the radionuclide 137Cs;
(c)X-rays generated from machine sources operated at or below an energy level of 5 MeV; or
(d)electrons generated from machine sources operated at or below an energy level of 10 MeV.