The charge of
the gold nucleus is Ze, where Z is the atomic number of the atom; for
gold Z = 79 Since the nucleus of gold is about 50 times heavier than an
a-particle, it is reasonable to assume that it remains stationary
throughout the scattering process Under these assumptions, the
trajectory of an alpha-particle can be computed employing Newton’s
second law of motion and the Coulomb’s law for electrostatic
force of repulsion between the alpha-particle and the positively
charged nucleus FIGURE 12