Radiation from metals bombarded by low-speed electrons

A small probe surface at a positive potential in a discharge may draw a cur- rent of many amperes per cm 2 with the potential gradient limited to a thin sheath over the surface. Under such conditions a continuous spectrum is emitted by metal surfaces in caesium, potassium, and helium discharges. With a copper probe at 7 volts in caesium vapor, the intensity J" (X) remains of the same magnitude between 6,200 and 2,400 A with a minimum at 5,800 and a maximum at 3,800.