⁴⁰K accounts for 0.0117% of naturally occurring potassium and potassium accounts for about 0.2% of the human body mass.Considering only the dominant decay of ⁴⁰K, which yields a β-decay electron of average energy 0.56 MeV, compute the average annual dose of radiation from potassium inside the body of a 70 kg person. Why can the exposure due to the γ-rays accompanying the electron capture decay be ignored in this estimate?