Soft X-rays and Secondary Electrons

Velocity distribution of photo-electrons excited by soft x-rays.—The apparatus was similar to that used in the magnetic analysis of $\beta$ rays. Soft x-rays excited by primary electrons with 150 to 1500 volts energy, fall on a radiator of W, Pt, Al, etc. The photo-electrons emitted in a plane approximately normal to the uniform magnetic field acting, each travel in a circle with a radius proportional to the speed; those of a given speed which pass through two fixed slits strike a photographic plate, after describing a semi-circle, along a line depending on their speed, thus giving a spectrum. The plates each show a sharp line with a considerable amount of energy right at the $h\nu$ limit corresponding to the energy of the primary electrons. A band due to electrons which had lost from 4 to 11 volts in coming out of the radiator, was also observed. These lines and bands indicate that free or loosely bound electrons are more readily ejected than internal electrons by soft x-rays. However, other lines were obtained due to electrons from various levels of the radiator atoms, with energies diminished by amounts corresponding to the critical potentials.