stream of electrons (as from a betatron) generated by heat ( thermionic emission), bombardment of charged atoms or particles (secondary electron emission), or strong electric fields (field emission). Electrons may be collimated by holes and slits, and, because they are electrically charged, they may be deflected, focused, and energized by electric and magnetic fields. Electron beams are used chiefly in research, technology, and medical therapy to produce X rays (X-ray) and images on television screens, oscilloscopes (cathode-ray oscilloscope), and electron microscopes (electron microscope).