It is usually assumed that alpha emitters don't deposit energy into neighboring tissues. Let's see if it is true. Assume that the kidney is a sphere of unit density (1 g/cm3) with a radius of 5 cm. Given that this kidney is uniformly contaminated with a radionuclide that emits 5 MeV alpha particles (assume a range of 20 microns in the kidney), estimate the fractional alpha energy loss from the kidney due to decays occurring at its edge. Make whatever simplifying assumptions you'd like to come up with a reasonable estimate.