A proton with charge \(+e\) is initially held at a distance \(r\) from a fixed helium nucleus with charge \(+2e\). An external agent moves the proton closer to the helium nucleus, decreasing the separation distance to \(\dfrac{r}{3}\). What is the ratio \(\dfrac{U_f}{U_i}\) of the final electric potential energy to the initial electric potential energy of the proton-nucleus system?