On The X-Ray Absorption Frequencies Characteristic of the Chemical Elements

Object.---The object of this paper is to record in some detail the data presented to the American Physical Society at its meeting on April 27, 1918¹.Blake and Duane² had determined the critical absorption wave-lengths associated with the K series of x-rays for most of the chemical elements from bromine (atomic number 35) to cerium (atomic number 58) by measuring the currents in an ionization chamber attached to an x-ray spectrometer. The research reported in this paper extends the measurements to chemical elements of lower atomic number, as far as manganese (atomic number 25). The same apparatus was used as in the previous research, except that the x-ray tube employed had a long glass tube attached to it carrying a thin glass window at its end. This window lay close to the spectrometer slit, and the device materially reduced the absorption of the long x-rays by the air and glass.Importance in Theory.---These critical absorption wave-lengths have considerable importance in connection with the theories of the structure of matter and the mechanism of radiation, for they represent frequencies of vibration that are the highest x-ray frequencies definitely known to be characteristic of the chemical elements.Results.---From the experiments it appears that the square root of the critical absorption frequency is not quite a linear function of the atomic number.If we calculate the velocity v of an electron in the x-ray tube required to produce the radiation from the equation I/2m₀v²√I-v²c²=hν using for ν the critical absorption frequency, we find that v is a linear function of N, namely v=v₀(N-3/2),v₀=.00678xc for all the chemical elements from manganese to cerium.Further equation (2) gives the critical velocity for the chemical elements as far as magnesium, if we use data obtained from emission spectra.It will be noticed that equation (1) contains the expression for the transverse mass of the electron.