Work Step by Step
In Rutherford’s model, the dense, tiny nucleus accounts for the backscattering of alpha particles. A very massive positively-charged nucleus is required, since the alpha particles are repelled with very little change in their kinetic energy. Rutherford concluded that the alpha particles bounced off something many times more massive than themselves. If the nucleus were larger and just as massive, a larger fraction of the incoming alpha particles would be backscattered, so he concluded the the nucleus must be small as well as massive. This is discussed on pages 603-604.