The alpha particle (that is, nucleus of a helium atom) includes two protons and two neutrons and consists of a mass of 6.64x 10^ -27 kg. The horizontal beam of alpha particles is injected with a speed of 1.3 x 10^5 m/s to the region having vertical magnetic field of magnitude .155 T. Determine how long does it take for an alpha particle to move half-way via a complete circle?