A proton and an alpha particle are separately projected in a  region where a uniform magnetic field exists. Their initial velocities are perpendicular to direction of magnetic field. If both the particles move in magnetic field in circles of equal radii, the ratio of momentum of proton to alpha particle $\left(\frac{{\mathrm{p}}_{\mathrm{p}}}{{\mathrm{p}}_{\mathrm{\alpha }}}\right)$ is

• A

  1

• B

  $\frac{1}{2}$

• C

  2

• D

  $\frac{1}{4}$