X-Ray Isochromats of Copper Taken in Different Directions Relative to the Cathode Stream

Variation with potential of the intensity of monochromatic x-rays of wave-lengths 0.823 to 0.247A for directions making angles of 36^∘{}, 90^∘{} and 144^∘{} with the cathode stream.---X-ray isochromats of copper were taken in three different directions relative to the cathode stream, for a target face making an angle of 25^∘{} with the cathode stream. Corrections were made for stray radiation in the neighborhood of the measured beam, for radiation due to secondary hits of cathode electrons which had been reflected backward from the focal spot at large angles, and for absorption in the target. It is established that, within experimental error, an isochromat of frequency ν varies linearly with the potential from potentials about (5/4) Hν to 2Hν, where Hν is the quantum voltage for excitation of frequency ν. The linear portions of the graphs were extrapolated to find the intercept on the intensity axis at Hν. This intercept depended on Hν, and also on θ, the angle between the measured x-rays and the cathode stream. For θ=90^∘ the intercepts varied between 0.062I^' (for Hν=50 kv.) and 0.085I^' (for Hν=15 kv.) with an average of 0.072I^'; for θ=36^∘ the respective values were 0.076I^', 0.096I^', 0.086I^'; for θ=144^∘, -0.035I^', 0.010I^', -0.017I^'. I^' is the intensity of the isochromat at 2Hν. Values of Hν used were 15, 20, 30, 40, 50 kv. The intercept decreased, in general, for increasing Hν, but for θ=36^∘ and θ=90^∘ the change was within the experimental error of ±0.01I^'.Energy distribution in the x-ray continuous spectrum from a thick target.---Kulenkampff's formula for the energy distribution in the x-ray continuous spectrum for θ=90^∘ does not hold in detail for the higher voltages and different target face inclination used in the present work. Assuming total energy in the continuous spectrum proportional to the square of the voltage on the tube, and assuming suitable modifications of this law, for the forward and backward angles, from Sommerfeld's space distribution of energy as a function of cathode ray velocity, it is shown that the spectrum for the forward angle contains relatively more high frequency rays than the spectrum at 90^∘{}, and the spectrum at the backward angle contains relatively more low frequency rays.Energy distribution in the x-ray continuous spectrum from a thin target.---On similar assumptions as to total energy, the spectra which would have been obtained from a very thin foil of copper are derived from the isochromats by Webster's method. The thin target spectra on a frequency scale, for θ=90^∘, are horizontal except for a sharp rise in intensity as ν approaches ν₀, the high frequency limit. For θ=36^∘ the energy is approximately directly proportional to ν except for the region near ν₀, where there is again the sharp increase. For θ=144^∘ the energy is approximately inversely proportional to ν except near ν₀ where there is a decrease for high voltages.Theories by Kramers and Wentzel for θ=90^∘ are in fair agreement with the experiments as to thick target spectra, but if certain assumptions made in this paper are correct, Kramers' predicted thin target spectra are much more nearly in accord with the facts than are Wentzel's.