Alpha Particles, Each Having a Charge Of $+ 2 e$ And a Mass Of

Alpha particles, each having a charge of $+ 2 e$ and a mass of $6.64 \times 10 ^ { - 27 } \mathrm {~kg}$ , are accelerated in a uniform $0.50 \mathrm {~T}$ magnetic field to a final orbit radius of $0.50 \mathrm {~m}$ . The field is perpendicular to the velocity of the particles. What is the kinetic energy of an alpha particle in the final orbit? $( 1 \mathrm { eV } =$ $\left. 1.60 \times 10 ^ { - 19 } \mathrm {~J} , e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

A) $3.0 \mathrm { MeV }$
B) $4.3 \mathrm { MeV }$
C) $3.4 \mathrm { MeV }$
D) $2.6 \mathrm { MeV }$
E) $3.9 \mathrm { MeV }$