Soft X-Rays

Abstract

Method.---Soft X-rays were produced by the impact of electrons from a hot-lime cathode against a platinum anode. Potentials of 20 to 1,000 volts were used to give the electrons the desired velocity of impact. The properties of the rays were studied by observing the velocity and number of electrons produced on a brass plate by a narrow beam of soft X-rays.Experimental Results.---(1) Soft X-rays were obtained with as low potentials as 20 volts. (2) Radioelectric curves were obtained under different experimental conditions. These curves have the general shape of photoelectric curves but differ from them in several important particulars. (3) The velocity distribution of radioelectrons was studied and it was found that only a negligible fraction of the electrons have velocities comparable with the velocity of impact of the cathode electrons. (4) Evidence was obtained of the presence of characteristic L-radiations of copper and zinc of approximate wave-lengths of 15 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ and 13 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ respectively and of softer characteristic rays of platinum of approximate wave-lengths of 21 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$ and 31 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}8}$. (5) It is pointed out that the method used in this investigation, which is called the radioelectric method, lends itself to the study of characteristic radiations of elements of low atomic numbers.