Soft X-Rays Produced by Cathode Rays of from 200 to 600 volts Velocities

Soft X-Rays, Examination of Method of Investigation Using No Window.---Previous results by the one author are briefly referred to, and a new experiment is described showing the difficulties in measuring a photoelectric effect due to soft X-rays produced in the same chamber as that which contains the photoelectric electrode.Soft X-Rays Produced by Cathode Rays of between 200 and 600 Volts Velocity, Effect of Occluded Gases in the Anticathode on the Intensity.---The method used for estimating the radiation produced was to allow the soft X-rays to ionize the gas in a chamber separated from the discharge tube by a thin celluloid window. (a) A platinum anticathode was partially denuded of gas by glowing, and (b) the remnants of gas in the tube were displaced by hydrogen, the intensity of radiation was not notably altered. The conclusion is drawn that the radiation observed comes from the solid anticathode.Variation of Intensity of Radiation with Voltage for Anticathodes of Brass, Platinum, Graphite, Aluminum, Lithium and for Gas Remnants, Air, Hydrogen, and Carbon Bisulphide.---After showing that the radiation is proportional to the cathode ray current, and that relative measurements could be fairly well repeated, even with different pressures of gas in the ionization chamber, the authors give details of the relative intensities and of the actual ionization current at 600 volts. The intensity at 300 volts was less than 2 per cent. that at 600 volts.Characteristic and General X-Radiation.---From a comparison of (a) the radiation from different anticathodes, and (b) the intensity as measured by ionization and by the photoelectric effect, it is inferred that the radiation is largely general. There is evidence of a characteristic (K) radiation from carbon, and one observation suggesting a characteristic (L) radiation from aluminum. At the end of the paper are found suggestions of possible reasons for the similarity of behaviour of different anticathodes.Soft X-Rays from 200 to 300 Volts.---It appears that the radiation in this region ionizes the gases used relatively less powerfully in proportion to its photoelectric effect.X-Radiation below 190 Volts.---Tests are described showing that the effects thus far obtained by the authors were due to gas in the tube and not to a radiation from the solid anticathode.