The emission of electrons from tungsten and molybdenum under the action of soft X-rays from copper

Abstract

The efficiency of many elements as emitters of soft X-rays has been investigated by Richardson and Robertson and others, using a photoelectric method. The X-ray exciting voltages used ranged up to 6000 volts and several metals were used as photoelectric detectors. Some phenomena observed in large thermionic valves indicated a need for information about the photoelectric emission from tungsten and molybdenum in particular, under the action of X-rays from copper at rather higher exciting voltages than those previously studied, and for this investigation it was decided to follow the technique developed by Professor Richardson and Mr. Robertson to whom I am indebted for helpful discussion of the subject and guidance in the design of the apparatus. The present results, therefore, form a continuation of the earlier work and extend it in several directions, principally the following: (1) the voltage range goes up to 20,000 volts; (2) tungsten and molybdenum were used as photoelectric detectors for X-rays from copper; and (3) an absorption screen, included in our apparatus, gave some indication of the quality of the radiation most effective in producing the emission. The effect of heat treatment of the photoelectric plates was also investigated and showed that the photoelectric emission is sensitive to the surface condition, but whether heat treatment produces an increase or a decrease in the emission depends on the previous treatment of the metal.