Medical cyclotrons need efficient sources of protons to inject into their center. In one kind of ion source, hydrogen atoms (i. e., protons with one orbiting electron) are fed into a chamber where there is a strong magnetic field. Electrons in this chamber are trapped in tight orbits, which greatly increases the chance that they will collide with a hydrogen atom and ionize it. One such source uses a magnetic field of 90 mTmT, and the electrons' kinetic energy is 1.4 eV. Required:
If the electrons travel in a plane perpendicular to the field, what is the radius of their orbits?