Suppose you are given a chance to repeat the ∝-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below 14 K). What result do you expect?
In the ∝-particle scattering experiment, if a thin sheet of solid hydrogen is used in place of a gold foil, then the scattering angle would not be large enough. This is because the mass of hydrogen is less than the mass of incident a-particles (6.64 X ${{10}^{-27}}$ kg). Thus, the mass of the scattering particle is more than the target nucleus (hydrogen). As a result, the a-particles would not bounce back, if solid hydrogen is used in the ∝-particles scattering experiment.