On The X-Ray Spectra of Tungsten

Abstract

Critical Absorption and Emission Wave-lengths in K and L Series.---This paper describes accurate measurements of the critical absorption wave-lengths associated with the K and the L series, and also of the wave-lengths of most of the emission lines in the L series. The measurements were made by means of a new ionization spectrometer, similar to the one described in the Physical Review for Dec., 1917, at page 624. A high tension storage battery supplied the current through the X-ray tube, the voltage and current being kept constant by the procedure indicated in the reference. To eliminate errors due to the penetration of the rays into the crystal and to lack of exact adjustment between the axis of rotation of the crystal and the effective reflecting plane, etc., the authors employed the third method mentioned in the article referred to, above. In this method two slits between the X-ray tube and the spectrometer define the width of the beam of X-rays that strikes the crystal, and the slit in front of the ionization chamber has sufficient breadth to allow the entire reflected beam to enter the chamber. With this arrangement of slits the angle through which the crystal turns (not the angle made by the reflected beam of rays with the zero of the instrument) measures the glancing angle that is used in the formula to calculate the wave-length.Mean Values of the Wave-lengths Measured in Spectra of the 1st, 2d and 3d Orders.---The following table contains the weighted mean values of the wave-lengths obtained from measurements in spectra of the 1st, 2d and 3d orders, together with an estimate of the precision of the measurements. To estimate the absolute accuracy of the data we must take into account the errors in the value of the grating constant of the calcite crystal used. These add up to about 0.07 per cent. In the text the values of the emission wave-lengths obtained by this ionization method are compared with those measurements of the same lines by photographic methods in which special procedures have been employed to minimize the effects of the above mentioned errors.