A proton and an $\alpha$-particle (with their masses in the ratio of $1: 4$ and charges in the ratio of $1: 2$ ) are accelerated from rest through a potential difference V . If a uniform magnetic field (B) is set up perpendicular to their velocities, the ratio of the radii $\mathrm{r}_{\mathrm{p} \text { m }} \mathrm{r}_\alpha$ of the circular paths described by them will be